Community Acquired Pneumonia

Community-Acquired Pneumonia

Community-acquired pneumonia develops in people with limited or no contact with medical institutions or settings. The most commonly identified pathogens are Streptococcus pneumoniae, Haemophilus influenzae, and atypical organisms (ie, Chlamydia pneumoniae, Mycoplasma pneumoniae, Legionella sp). Symptoms and signs are fever, cough, pleuritic chest pain, dyspnea, tachypnea, and tachycardia. Diagnosis is based on clinical presentation and chest x-ray. Treatment is with empirically chosen antibiotics. Prognosis is excellent for relatively young or healthy patients, but many pneumonias, especially when caused by S. pneumoniae or influenza virus, are fatal in older, sicker patients. Etiology Many organisms cause community-acquired pneumonia, including bacteria, viruses, and fungi. Pathogens vary by patient age and other factors, but the relative importance of each as a cause of community-acquired pneumonia is uncertain, because most patients do not undergo thorough testing, and because even with testing, specific agents are identified in < 50% of cases. S. pneumoniae, H. influenzae, C. pneumoniae, and M. pneumoniae are the most common bacterial causes. Pneumonia caused by chlamydia and mycoplasma are often clinically indistinguishable from pneumonias with other causes. Common viral agents include respiratory syncytial virus (RSV), adenovirus, influenza viruses, metapneumovirus, and parainfluenza viruses. Bacterial superinfection can make distinguishing viral from bacterial infection difficult. C. pneumoniae accounts for 2 to 5% of community-acquired pneumonia and is the 2nd most common cause of lung infections in healthy people aged 5 to 35 yr. C. pneumoniae is commonly responsible for outbreaks of respiratory infection within families, in college dormitories, and in military training camps. It causes a relatively benign form of pneumonia that infrequently requires hospitalization. Chlamydia psittaci pneumonia (psittacosis) is rare and occurs in patients who own or are often exposed to birds. A host of other organisms cause lung infection in immunocompetent patients, although the term community-acquired pneumonia is usually reserved for the more common bacterial and viral etiologies. Q fever, tularemia, anthrax, and plague are uncommon bacterial syndromes in which pneumonia may be a prominent feature; the latter three should raise the suspicion of bioterrorism. Adenovirus, Epstein-Barr virus, and coxsackievirus are common viruses that rarely cause pneumonia. Varicella virus and hantavirus cause lung infection as part of adult chickenpox and hantavirus pulmonary syndrome; a coronavirus causes severe acute respiratory syndrome. Common fungal pathogens include Histoplasma capsulatum (histoplasmosis) and Coccidioides immitis (coccidioidomycosis). Less common fungi include Blastomyces dermatitidis (blastomycosis) and Paracoccidioides braziliensis (paracoccidioidomycosis). Pneumocystis jiroveci commonly causes pneumonia in patients who have HIV infection or are immunosuppressed. Parasites causing lung infection in developed countries include Toxocara canis or T. catis (visceral larva migrans), Dirofilaria immitis (dirofilariasis), and Paragonimus westermani (paragonimiasis). Symptoms and Signs Symptoms include malaise, cough, dyspnea, and chest pain. Cough typically is productive in older children and adults and dry in infants, young children, and the elderly. Dyspnea usually is mild and exertional and is rarely present at rest. Chest pain is pleuritic and is adjacent to the infected area. Pneumonia may manifest as upper abdominal pain when lower lobe infection irritates the diaphragm. Symptoms become variable at the extremes of age; infection in infants may manifest as nonspecific irritability and restlessness; in the elderly, as confusion and obtundation. Signs include fever, tachypnea, tachycardia, crackles, bronchial breath sounds, egophony, and dullness to percussion. Signs of pleural effusion may also be present. Nasal flaring, use of accessory muscles, and cyanosis are common in infants. Fever is frequently absent in the elderly. Symptoms and signs were previously thought to differ by type of pathogen, but presentations overlap considerably. In addition, no single symptom or sign is sensitive or specific enough to predict the organism. Symptoms are even similar for noninfective lung diseases such as pulmonary embolism, pulmonary malignancy, and other inflammatory lung diseases. Diagnosis •

Chest x-ray

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Consideration of pulmonary embolism

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Sometimes identification of pathogen

Diagnosis is suspected on the basis of clinical presentation and is confirmed by chest x-ray. The most serious condition misdiagnosed as pneumonia is pulmonary embolism, which may be more likely in patients with minimal sputum production, no accompanying URI or systemic symptoms, and risk factors for thromboembolism. Chest x-ray almost always demonstrates some degree of infiltrate; rarely, an infiltrate is absent in the first 24 to 48 h of illness. In general, no specific findings distinguish one type of infection from another, although multilobar infiltrates suggest S. pneumoniae or Legionella pneumophila infection and interstitial pneumonia suggests viral or mycoplasmal etiology. Hospitalized patients should undergo WBC count and electrolytes, BUN, and creatinine testing to classify risk and hydration status. Two sets of blood

cultures are often obtained to detect pneumococcal bacteremia and sepsis, because about 12% of all patients hospitalized with pneumonia have bacteremia; S. pneumoniae accounts for 2⁄3 of these cases. Whether the results of blood cultures alter therapy commonly enough to warrant the expense is under study. Pulse oximetry or ABG should also be done. Pathogens: Attempts to identify a pathogen are not routinely indicated; exceptions may be made for critically ill patients, patients in whom a drugresistant or unusual organism is suspected (eg, TB, P. jiroveci), and patients who are deteriorating or not responding to treatment within 72 h. The use of Gram stain and culture of sputum for diagnosis is of uncertain benefit, because specimens often are contaminated and because overall diagnostic yield is low. Samples can be obtained noninvasively by simple expectoration or after hypertonic saline nebulization for those unable to produce sputum. Alternatively, patients can undergo bronchoscopy or endotracheal suctioning, either of which can be easily done through an endotracheal tube in mechanically ventilated patients. Testing should include mycobacterial and fungal stains and cultures in patients whose condition is deteriorating and in those unresponsive to broad-spectrum antibiotics. Additional tests are indicated in some circumstances. Patients at risk of Legionella pneumonia (eg, patients who smoke, have chronic pulmonary disease, are > 40, receive chemotherapy, or take immunosuppressants for organ transplantation) should undergo testing for urinary Legionella antigen, which remains present long after treatment is initiated, but the test detects only L. pneumophila serogroup 1 (70% of cases). A 4-fold rise in antibody titers to ≥ 1:128 (or a single titer of ≥ 1:256 in a convalescent patient) is also considered diagnostic. These tests are specific (95 to 100%) but are not very sensitive (40 to 60%); thus, a positive test indicates infection, but a negative test does not exclude it. Infants and young children with possible RSV infection should undergo rapid antigen testing of specimens obtained with nasal or throat swabs. No other tests for viral pneumonias are done; viral culture and serologic tests are rarely clinically warranted. PCR testing for mycoplasma and chlamydia species, although not widely available, holds promise as a highly sensitive and specific rapid diagnostic test and is likely to play a greater role as PCR technologies are refined. Prognosis Pneumococcal infection accounts for about 66% of fatal cases of communityacquired pneumonia in which an etiologic agent is known. The overall mortality rate in hospitalized patients is about 12%. Poor prognostic factors include age < 1 or > 60 yr; involvement of more than one lobe; peripheral WBC count < 5000/μL; comorbidities (eg, heart failure, alcoholism, hepatic or renal insufficiency), immunosuppression (eg, agammaglobulinemia, anatomic or functional asplenia), infection with serotypes 3 and 8; and hematogenous spread with either positive blood cultures or extrapulmonary complications (usually arthritis, meningitis, endocarditis). Infants and children are at special risk of pneumococcal otitis media, bacteremia, and meningitis. Mortality in Legionella infection is 10 to 20% among community-acquired cases and is higher among immunosuppressed or hospitalized patients. Patients who respond do so slowly, and x-ray abnormalities usually persist for ≥ 1 mo. Most patients require hospitalization, many require ventilator support, and 10 to 20% die despite appropriate antibiotic therapy. Prognosis in mycoplasma pneumonia is excellent; nearly all patients recover. Chlamydophila pneumoniae responds more slowly to treatment than mycoplasma pneumonia and tends to recur if therapy is stopped prematurely. Young adults with C. pneumoniae usually do well, but the elderly have a mortality rate of 5 to 10%. Treatment •

Risk stratification

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Antibiotics

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Antivirals for influenza or varicella

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Supportive measures

A prediction rule may be used to estimate mortality risk. The rule has been used to identify those patients who can be safely treated as outpatients and those who require hospitalization because of high risk of complications. However, the rule was not developed to determine site of care. Thus, the rule should supplement, not replace, clinical judgment, because many unrepresented factors, such as likelihood of adherence, ability to care for self, and wishes to avoid hospitalization, should also influence triage decisions.Also, certain criteria that extend across a continuum of severity have dichotomous cutoffs; eg, a heart rate of 124 beats/min may indicate distress, but points are not assigned unless heart rate is ≥ 125 beats/min. ICU admission is required for patients who need mechanical ventilation and for those with hypotension (systolic BP < 90 mm Hg) that is unresponsive to volume resuscitation. Other criteria that mandate consideration for ICU admission include respiratory rate > 30/min, Pao2/inspired O2 (Fio2) < 250, multilobar pneumonia, diastolic BP < 60 mm Hg, confusion, and BUN > 19.6 mg/dL. Appropriate treatment involves starting antibiotics as soon as possible, preferably ≤ 8 h after presentation. Supportive care includes fluids, antipyretics, analgesics, and for patients with hypoxemia O2. Because organisms are difficult to identify, antibiotics are selected based on likely pathogens and severity of illness. Guidelines should be adapted to local susceptibility patterns, drug formularies, and individual patient circumstances. Importantly, none provide recommendations for treatment of viral pneumonia.

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Community-acquired pneumonia (CAP) is an infection of the alveoli, distal airways, and interstitium of the lungs that occurs outside the hospital setting. Characterized clinically by

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Fever, chills, cough, pleuritic chest pain, sputum production

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At least 1 opacity on chest radiography

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Manifests as 4 general patterns ○ ○

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Lobar pneumonia: involvement of an entire lung lobe Bronchopneumonia: patchy consolidation in 1 or several lobes, usually in dependent lower or posterior portions centered around bronchi and bronchioles Interstitial pneumonia: inflammation of the interstitium, including the alveolar walls and connective tissue around the bronchovascular tree Miliary pneumonia: numerous discrete lesions due to hematogenous spread

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End-stage renal disease

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HIV infection

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Recent hotel stay or ship cruise

Risk factors for gram-negative bacterial pneumonia (including that caused by Pseudomonas aeruginosa) ○

Probable aspiration

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Previous hospital admission

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Previous antimicrobial treatment

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Bronchiectasis

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Neutropenia

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Comorbidities such as alcoholism, heart failure, or renal failure

Alcohol use

Independent risk factors for CAP include: ○

Alcoholism (relative risk [RR] 9)

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Asthma (RR 4.2)

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Immunosuppression (RR 1.9)

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Institutionalization

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Age > 70 years (RR 1.5 vs 60–69 years)

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Dementia

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Seizures

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Congestive heart failure

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Cerebrovascular disease

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Tobacco smoking

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Alcoholism

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Chronic obstructive pulmonary disease (COPD)

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HIV infection Risk up to 40 times that in age-matched patients not infected with HIV

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Male sex

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African-American race

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Chronic illness

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Current tobacco smoking (strongest independent predictor among immunocompetent young adults)

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Passive exposure to tobacco smoke

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Immunologic defects 

Multiple myeloma

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Nephrotic syndrome with low serum immune globulin levels

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Splenectomy

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HIV infection

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Others

Risk factors for community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) ○

Native-American race

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Homeless youths

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Men who have sex with men

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Prison inmates

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Military recruits

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Children in day-care centers

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Athletes such as wrestlers

Risk factors for Legionnaires’ disease include: ○

Male sex

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Current tobacco smoking

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Diabetes

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Hematologic malignancy

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Higher incidence of gram-negative bacterial pneumonia

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Worse clinical symptoms

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Require longer courses of IV antibiotic therapy than do nondrinkers

More prolonged fever, slower resolution, and a higher rate of empyema have been noted in pneumococcal pneumonia patients with chronic alcoholism than in their nondrinking counterparts.

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The clinical entity designated ALPS—alcoholism, leukopenia, and pneumococcal sepsis—is associated with a mortality rate of 80%.

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Excessive alcohol use is an independent risk factor for the development of acute respiratory distress syndrome (ARDS).

Epidemiologic risk factors suggesting possible causes of CAP ○

Alcoholism

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P. aeruginosa, Burkholderia cepacia, S. aureus

Dementia, stroke, decreased level of consciousness 

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Haemophilus influenzae, Pseudomonas aeruginosa, Legionella spp., S. pneumoniae, Moraxella catarrhalis, Chlamydophila pneumoniae

Structural lung disease (e.g., bronchiectasis)

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Streptococcus pneumoniae, oral anaerobes, Klebsiella pneumoniae, Acinetobacter spp., Mycobacterium tuberculosis

COPD and/or smoking

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Risk factors for invasive pneumococcal disease include: ○

Heavy drinkers (i.e., those consuming > 100 g of ethanol per day for the preceding 2 years)

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Risk factors for pneumococcal pneumonia include:

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Cancer

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Risk Factors •

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Oral anaerobes, gram-negative enteric bacteria

Lung abscess

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CA-MRSA, oral anaerobes, endemic fungi, M. tuberculosis, atypical mycobacteria

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Travel to Ohio or St. Lawrence river valleys

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Travel to southwestern U.S.

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Hantavirus, Coccidioides spp.

Travel to Southeast Asia

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Histoplasma capsulatum

Burkholderia pseudomallei, avian influenza virus

Stay in hotel or on cruise ship in previous 2 weeks

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Legionella spp.

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Local influenza activity

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Exposure to bats or birds

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Influenza virus, S. pneumoniae, S. aureus

H. capsulatum

Exposure to birds

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Chlamydophila psittaci

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Exposure to rabbits

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Francisella tularensis

Exposure to sheep, goats, parturient cats

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Coxiella burnetii

Etiology •

Most cases of CAP are caused by a few common respiratory pathogens, including:

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S. pneumoniae 

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H. influenzae

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S. aureus

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Accounts for ~50% of all cases of CAP requiring hospital admission • MRSA

Pleuritic chest pain

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Chills and/or rigors

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Dyspnea

Frequent signs/symptoms 

Headache

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Nausea

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Vomiting

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Diarrhea

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Fatigue

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Arthralgia/myalgia

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Falls and new-onset or worsening confusion (in elderly patients)

Physical findings ○

Fever

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Tachypnea

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M. pneumoniae

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C. pneumoniae

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M. catarrhalis

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Legionella spp.

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Aerobic gram-negative bacteria

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Influenza viruses

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Adenoviruses

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Respiratory syncytial virus (RSV)

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Dullness to percussion

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Other rare organisms

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Vocal fremitus

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Decreased tactile fremitus: reflects pleural fluid

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Egophony

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Crackles

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Pleural friction rub

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Viral: hantavirus, Nipah virus, Hendra virus, metapneumovirus, severe acute respiratory syndrome (SARS) virus, coronavirus

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Nonviral: Pneumocystis , Mycobacterium tuberculosis , fungi, bioterrorism agents (e.g., those of Q fever, tularemia, anthrax, plague), etc.

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Data suggest that a virus may be responsible in up to 18% of cases of CAP that require admission to the hospital.

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~10–15% of CAP cases are polymicrobial.

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Microaspiration of oropharyngeal secretions colonized with pathogenic microorganisms (e.g., S. pneumoniae , H. influenzae ) is the most common route.

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Gross aspiration 

Central nervous system disorders that affect swallowing (e.g., stroke, seizures)

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Impaired consciousness (e.g., in alcoholism, IV drug use)

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Anesthesia or intubation

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Pathogens include anaerobic organisms and gram-negative bacilli.

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Anaerobes play a significant role only when an episode of aspiration has occurred days to weeks before presentation for pneumonia.

Patients with a heart rate of ≥100/min, a temperature of ≥37.8°C, and a respiratory rate of ≥20/min were 5 times more likely to have pneumonia than patients without these findings in 1 study.

Chest examination

Increased tactile fremitus: reflects underlying consolidated lung

Whispering pectoriloquy

Elderly ○

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Pathogenesis

In 2 studies, patients with a respiratory rate of > 25/min had a pneumonia likelihood ratio of 1.5–3.4.

Tachycardia 

The relative frequency of these pathogens differs with the patient’s age and the severity of pneumonia.

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May initially display new-onset or worsening confusion and few other manifestations

Severely ill patients who have septic shock secondary to CAP ○

Hypotension and evidence of organ failure

Diagnostic Approach •

Assess pneumonia severity. ○

Pay attention to vital signs, including oxygen saturation.

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Always count the respiratory rate yourself for 1 min. 

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The single most useful clinical sign of severity is a respiratory rate of > 30/min in a person without underlying lung disease.

Ensure adequate oxygenation and support of circulation during the evaluation.

Consider possible etiologies. ○

Anaerobic pneumonias are often complicated by abscess formation and significant empyemas or parapneumonic effusions.

Carefully collect information on: 

Travel

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Occupational and other exposures

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Underlying illnesses

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Prior infections

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Aerosolization (e.g., of M. tuberculosis, Legionella spp., viruses)

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Hematogenous spread (e.g., seeding of the lungs by S. aureus during endocarditis)

Never forget tuberculosis and Pneumocystis infection as possible etiologies.

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Contiguous spread from another site

Consider pulmonary embolus in all patients with pleuritic chest pain.

Symptoms & Signs •

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History ○

Most typical signs/symptoms 

Fever

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Cough (nonproductive or productive of purulent sputum)

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Perform etiologic workup. ○

Chest x-ray

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Sputum stains and cultures

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Blood cultures, if bacteremia is likely

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Urine antigen tests for S. pneumoniae and Legionella pneumophila type 1 can be helpful.

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Serology can be helpful in identifying certain pathogens.

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Because of the low yield (positivity rate: 5–14%) and the lack of significant impact on outcome, blood cultures are no longer considered de rigueur for all hospitalized patients with CAP. ○

Certain high-risk patients—including those with the following conditions—should have blood cultured.

Laboratory Tests Nonspecific studies •

Assessment of the severity of pneumonia and coexisting disease ○

Arterial blood gas

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Complete blood count

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Serum electrolyte and glucose measurements

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Blood urea nitrogen and creatinine measurements

Sputum stains and culture •

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L. pneumophila (See Legionellosis.) Serogroup 1 antigen can be detected in the urine of patients with Legionnaires’ disease by enzyme-linked immunosorbent assay (ELISA).

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Significant interobserver variability exists in the interpretation of gram-stained sputum smears.

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Results may be negative early in the illness.

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Can detect antigen even after initiation of appropriate antibiotic therapy and after weeks of illness

The presence of any gram-positive diplococci has a sensitivity of 100% but a specificity of 0 for a diagnosis of pneumococcal infection. The presence of > 10 gram-positive diplococci per oil-immersion field has a sensitivity of 55% and a specificity of 85% for this diagnosis.

Stains for: 

Acid-fast bacilli

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Pneumocystis

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Fungi

Cytology

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This test should be used for patients in whom Legionnaires’ disease is strongly suspected, including those with rapidly progressive pneumonia.

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The urine antigen test is now the most frequently used diagnostic method for Legionnaires’ disease.

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Infection with Legionella spp. other than L. pneumophila serogroup 1 gives a negative test result.

S. pneumoniae ○

The pneumococcal urine antigen test is also quite sensitive and specific (80% and >90%, respectively).

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Can detect antigen even after the initiation of appropriate antibiotic therapy and after weeks of illness

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In children, nasopharyngeal carriage of S. pneumoniae can result in a positive urinary antigen test.

Other antigen tests

Culture Results should always be correlated with those of Gram staining. 

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If an organism is isolated from sputum and its morphologic correlate is not seen on Gram staining, the isolate may be colonizing the upper airway.

Certain microorganisms, if isolated from sputum, should always be considered pathogens. These include:

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M. tuberculosis

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Rapid tests for influenza virus

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Direct fluorescent antibody tests for influenza virus and RSV 

The test for RSV is only poorly sensitive.

Serology

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Detection of IgM antibody or demonstration of a 4-fold rise in titer of antibody to a particular agent between acute- and convalescentphase serum samples generally is considered good evidence that this agent is the cause of CAP.

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The following etiologic agents often are diagnosed serologically:

Legionella spp. Blastomyces dermatitidis

Sample: nasopharyngeal swab, respiratory secretions

H. capsulatum

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M. pneumoniae

Coccidioides immitis

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C. pneumoniae

Only about one-third of elderly patients admitted with CAP produce sputum suitable for culture.

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C. psittaci

One-third of these specimens fail to yield a pathogen.

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Legionella spp.

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Coxiella burnetii

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Adenovirus

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Parainfluenza viruses

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Influenza virus A

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For patients admitted to the ICU and intubated, a deep-suction aspirate or bronchoalveolar lavage sample should be sent to the microbiology laboratory as soon as possible.

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Cultures of pleural fluid obtained from effusions >1 cm in height on a lateral decubitus chest radiograph may also be helpful.

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Blood should be obtained for culture from patients to be treated on an ambulatory basis if they have been receiving antibiotic therapy and have presented because of any of the following:

Serologic tests include complement fixation, indirect immunofluorescence, and ELISA.

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Separate IgM and IgG antibody detection tests can be performed with the latter 2 assays.

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Hyperthermia (body temperature > 38.5°C)

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Hypothermia (body temperature < 36°C)

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Homelessness

One difficulty in relying on serology is that a polyclonal antibody response to 1 agent may result in a 4-fold rise in antibody titer to others.

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Alcohol abuse

Blood culture •

Severe CAP

The sensitivity and specificity of the Legionella urine antigen test are as high as 90% and 99%, respectively.

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Rapid antigen testing for viral pathogens (e.g., influenza)

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Chronic liver disease

A sputum sample with > 25 neutrophils and < 10 squamous epithelial cells per lowpower field is suitable for culture.

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Complement deficiencies

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Other sputum studies that may be helpful in some patients ○

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Asplenia

The most common isolates, in descending order, are S. pneumoniae (~60%), S. aureus , and Escherichia coli .

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Useful in screening a sputum sample for suitability for culture and in making a presumptive etiologic diagnosis

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Neutropenia

Detection of antigens of pulmonary pathogens in urine

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Gram’s stain ○

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Thus results may be nonspecific.

Serologic testing is not recommended for routine use.

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If agents such as C. burnetii are suspected, serologic testing is necessary.

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Serology is a useful part of the workup of outbreaks of pneumonia associated with negative blood and sputum cultures.

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Recently, serologic testing has fallen out of favor because of the time required to obtain a final result for a convalescent-phase sample.

Polymerase chain reaction (PCR) •

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Amplification of the DNA or RNA of microorganisms that are not part of the pharyngeal flora (from microbial cells collected by throat swab) has been used to infer that the implicated microorganism is the cause of pneumonia.

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A multiplex PCR allows detection of DNA of Legionella spp., M. pneumoniae, and C. pneumoniae. This test is expensive and is not routinely available.

Imaging •

Chest x-ray ○

Diagnostic test of choice for pneumonia

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May show lobar consolidation, interstitial infiltrates, cavitation, associated pleural fluid, etc.

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Occasionally, an etiologic diagnosis is suggested by chest radiography findings.

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A cavitating upper-lobe lesion raises the likelihood of tuberculosis.

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Pneumatoceles suggest S. aureus pneumonia.

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An air-fluid level suggests a pulmonary abscess, which often is polymicrobial.

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In the immunocompromised host, a crescent (meniscus) sign suggests aspergillosis.

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In most instances, no etiologic inference can be made from radiographic abnormalities, despite the traditional teaching that a lobar vs interstitial appearance may be more suggestive of "typical" bacterial vs "atypical" bacterial or nonbacterial etiologies.

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If pneumonia is strongly suspected on clinical grounds and no opacity is seen on the initial chest radiograph, it is useful to repeat the radiograph in 24–48 hours or to perform CT. 

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Correction of dehydration may lead to development of chest film infiltrates.

Opacity visible on the chest radiograph may not be due to pneumonia; many other disease processes can result in opacities (see Differential Diagnosis).

High-resolution CT ○

Rarely necessary

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Occasionally detects pulmonary opacities in patients with symptoms and signs suggestive of pneumonia and negative chest x-ray

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More likely than chest radiography to show bilateral involvement, pleural fluid/empyema, adenopathy, etc.

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May be of value in a patient with suspected postobstructive pneumonia caused by a tumor or foreign body

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If a pleural effusion of > 1 cm is detected on lateral decubitus chest x-ray, the fluid should be sampled for studies including Gram’s stain, culture, cell counts, and measurements of protein, lactate dehydrogenase (LDH), glucose, and pH.

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Bronchoscopy/bronchoalveolar lavage/lung biopsy: ○

May be required to obtain material for further studies when the diagnosis defies other diagnostic efforts and the patient does not improve despite empirical therapy

Prognosis •

Inpatients ○

Patients generally stabilize within 3–7 days.

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The in-hospital mortality rate from pneumonia is ~10%.

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~50% of deaths are directly attributable to pneumonia and ~50% to comorbid illnesses.

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Pneumonia-related deaths are much more likely to occur during the first week of hospitalization.

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Increasing age and evidence of aspiration independently predict both pneumonia- and comorbidity-related mortality.

Factors independently associated with pneumoniaunrelated mortality include: 

Dementia

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Immunosuppression

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Active cancer

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Systolic hypotension

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Male sex

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Multilobar pulmonary infiltrates

Mortality associated with PORT score (See Treatment Approach.) 

Class I: 0–0.5%

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Class II: 0.4–0.9%

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Class III: 0–1.25%

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Class IV: 9.0–12.5%

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Class V: 27.1%

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Rates are highest (>50%) for P. aeruginosa, followed by Klebsiella spp., E. coli, S. aureus, and Acinetobacter spp. (all 30–35%).

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Pneumococcal capsular serotype 3 is associated with a much higher mortality rate than serotype 1, as are group A streptococcal M serotypes 1 and 3 (compared with other serotypes).

Early, appropriate antibiotic therapy is associated with decreased mortality rates.

Prevention •

Influenza and pneumococcal vaccination status should be ascertained and vaccines offered when appropriate.

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All patients with pneumonia who are tobacco smokers should be encouraged to join smoking cessation programs.

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When a patient is prone to aspiration, preventive measures should be taken, including attention to oral hygiene.

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Only sterile water should be used in humidifiers in long-term-care facilities.

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Antimicrobial prophylaxis should be given in special situations, including the following:

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Latent tuberculosis prophylaxis (See Tuberculosis.)

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Pneumocystis prophylaxis for selected immunocompromised patients (See Pneumocystis Infections.)

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In the event of an influenza outbreak, unprotected patients at risk from complications should be:

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Thoracentesis

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The most common immediate causes of death are respiratory failure, heart disease, and sepsis.

Mortality is related to specific etiology.

Diagnostic Procedures

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Vaccinated immediately and Given chemoprophylaxis with either oseltamivir or zanamivir for 2 weeks

Complete Blood Count How is it used? The CBC is used as a broad screening test to check for such disorders as anemia, infection, and many other diseases. It is actually a panel of tests that examines different parts of the blood and includes the following:

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White blood cell (WBC) count is a count of the actual number of white blood cells per volume of blood. Both increases and decreases can be significant.

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White blood cell differential looks at the types of white blood cells present. There are five different types of white blood cells, each with its own function in protecting us from infection. The differential classifies a person's white blood cells into each type: neutrophils (also known as segs, PMNs, granulocytes, grans), lymphocytes, monocytes, eosinophils, and basophils.

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Red blood cell (RBC) count is a count of the actual number of red blood cells per volume of blood. Both increases and decreases can point to abnormal conditions.

Test Eos Baso

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Hemoglobin measures the amount of oxygen-carrying protein in the blood.

RBC

•

Hematocrit measures the percentage of red blood cells in a given volume of whole blood.

•

The platelet count is the number of platelets in a given volume of blood. Both increases and decreases can point to abnormal conditions of excess bleeding or clotting. Mean platelet volume (MPV) is a machine-calculated measurement of the average size of your platelets. New platelets are larger, and an increased MPV occurs when increased numbers of platelets are being produced. MPV gives your doctor information about platelet production in your bone marrow.

•

•

•

•

Mean corpuscular volume (MCV) is a measurement of the average size of your RBCs. The MCV is elevated when your RBCs are larger than normal (macrocytic), for example in anemia caused by vitamin B12 deficiency. When the MCV is decreased, your RBCs are smaller than normal (microcytic) as is seen in iron deficiency anemia or thalassemias. Mean corpuscular hemoglobin (MCH) is a calculation of the average amount of oxygen-carrying hemoglobin inside a red blood cell. Macrocytic RBCs are large so tend to have a higher MCH, while microcytic red cells would have a lower value. Mean corpuscular hemoglobin concentration (MCHC) is a calculation of the average concentration of hemoglobin inside a red cell. Decreased MCHC values (hypochromia) are seen in conditions where the hemoglobin is abnormally diluted inside the red cells, such as in iron deficiency anemia and in thalassemia. Increased MCHC values (hyperchromia) are seen in conditions where the hemoglobin is abnormally concentrated inside the red cells, such as in burn patients and hereditary spherocytosis, a relatively rare congenital disorder. Red cell distribution width (RDW) is a calculation of the variation in the size of your RBCs. In some anemias, such as pernicious anemia, the amount of variation (anisocytosis) in RBC size (along with variation in shape – poikilocytosis) causes an increase in the RDW.

When is it ordered? The CBC is a very common test. Many patients will have baseline CBC tests to help determine their general health status. If they are healthy and they have cell populations that are within normal limits, then they may not require another CBC until their health status changes or until their doctor feels that it is necessary. If a patient is having symptoms such as fatigue or weakness or has an infection, inflammation, bruising, or bleeding, then the doctor may order a CBC to help diagnose the cause. Significant increases in WBCs may help confirm that an infection is present and suggest the need for further testing to identify its cause. Decreases in the number of RBCs (anemia) can be further evaluated by changes in size or shape of the RBCs to help determine if the cause might be decreased production, increased loss, or increased destruction of RBCs. A platelet count that is low or extremely high may confirm the cause of excessive bleeding or clotting and can also be associated with diseases of the bone marrow such as leukemia. Many conditions will result in increases or decreases in the cell populations. Some of these conditions may require treatment, while others will resolve on their own. Some diseases, such as cancer (and chemotherapy treatment), can affect bone marrow production of cells, increasing the production of one cell at the expense of others or decreasing overall cell production. Some medications can decrease WBC counts while some vitamin and mineral deficiencies can cause anemia. The CBC test may be ordered by the doctor on a regular basis to monitor these conditions and drug treatments.

Hgb Hct MCV MCH MCHC

RDW

Platelet

MPV

Blood Smear and WBC. Decreased with anemia; increased when too many made and with fluid Red Blood Cell loss due to diarrhea, dehydration, burns Hemoglobin Mirrors RBC results Hematocrit Mirrors RBC results Increased with B12 and Folate Mean Corpuscular Volume deficiency; decreased with iron deficiency and thalassemia Mean Corpuscular Mirrors MCV results Hemoglobin May be decreased when MCV is Mean Corpuscular decreased; increases limited to Hemoglobin Concentration amount of Hgb that will fit inside a RBC Increased RDW indicates mixed RBC Distribution Width population of RBCs; immature RBCs tend to be larger Decreased or increased with conditions that affect platelet production; decreased when greater numbers used, as with bleeding; decreased with some inherited Platelet disorders (such as Wiskott-Aldrich, Bernard-Soulier), with Systemic lupus erythematosus, pernicious anemia, hypersplenism (spleen takes too many out of circulation), leukemia, and chemotherapy Vary with platelet production; Mean Platelet Volume younger platelets are larger than older ones

Medical urinalysis A typical medical urinalysis usually includes:

• •

a description of color and appearance.

• •

pH - normally 4.8 to 7.5.

• •

proteins - normally negative (absent)

The following table explains what increases or decreases in each of the components of the CBC may mean. Components of the CBC Increased/decreased May be increased with infections, inflammation, cancer, leukemia; decreased with some medications (such as methotrexate), some autoimmune conditions, some severe infections, bone marrow failure, and congenital marrow aplasia (marrow doesn't develop normally) % This is a dynamic population that Neutrophil/Band/Seg/Gran Neutrophil varies somewhat from day to day depending on what is going on in the Lymphs Lymphocyte body. Significant increases in % Mono Monocyte particular types are associated with % Eos Eosinophil different temporary/acute and/or % Baso Basophil chronic conditions. An example of Neutrophil Neutrophil/Ban/Seg/Gran this is the increased number of lymphocytes seen with lymphocytic Lymphs Lymphocyte leukemia. For more information, see Mono Monocyte

Increased/decreased

Urinalysis A urinalysis (or "UA") is an array of tests performed on urine and one of the most common methods of medical diagnosis.[1] A part of a urinalysis can be performed by using urine dipsticks, in which the test results can be read as color changes.

What does the test result mean?

Test WBC

Name Eosinophil Basophil

Name White Blood Cell

specific gravity - normally 1.002 to 1.028. This test detects ion concentration of the urine. Small amounts of protein or ketoacidosis tend to elevate results of the specific gravity. Specific gravity is an expression of the weight of a substance relative to the weight of an equal volume of water. Water has a specific gravity of one. The specific gravity of your urine is measured by using a urinometer. Knowing the specific gravity of your urine is very important because the number indicates whether you are hydrated or dehydrated. If the specific gravity of your urine is under 1.007, you are hydrated. If your urine is above 1.010, you are dehydrated.

ketone bodies - normally negative (absent). When there is carbohydrate deprivation, such as starvation or high protein diets, the body relies increasingly on the metabolism of fats for energy. This pattern is also seen in people with the disease diabetes mellitus, when a lack of the hormone insulin prevents the body cells from utilizing the large amounts of glucose available in the blood. This happens because insulin is necessary for the transport of glucose from the blood into the body cells. The metabolism of fat proceeds in a series of steps. First, triglycerides are hydrolyzed to fatty acids and glycerol. Second the fatty acids are hydrolyzed into smaller intermediate compounds (acetoacetic acid, betahydroxybutyric acid, and acetone). Thirdly, the intermediate products are utilized in aerobic cellular respiration. When the production of the intermediate products of fatty acid metabolism (collectively known as ketone bodies) exceeds the ability of the body to metabolize these compounds they accumulate in the blood and some end up in the urine (ketonuria).

Albustix Test - Since proteins are very large molecules (macromolecules), they are not normally present in measurable amounts in the glomerular

filtrate or in the urine. The detection of proteins in your urine may indicate that the permeability of the glomerulus is abnormally increased. This may be caused by renal infections or it may be caused by other diseases that have secondarily affected the kidneys such as diabetes mellitus, jaundice, or hyperthyroidism.

• • •

nitrites urobilinogen Bilirubin - The fixed phagocytic cells of the spleen and bone marrow destroy old red blood cells and convert the heme groups of hemoglobi to the pigment bilirubin. The bilirubin is secreted into the blood and carried to the liver where it is bonded to (conjugated with) glucuronic acid, a derivative of glucose. Some of the conjugated bilirubin is secreted into the blood and the rest is excreted in the bile as bile pigment that passes into the small intestine. The blood normally contains a small amount of free and conjugated bilirubin. An abnormally high level of blood bilirubin may result from: an increased rate of red blood cell destruction, liver damage, as in hepatitis and cirrhosis, and obstruction of the common bile duct as with gallstones. An increase in blood bilirubin results in jaundice, a condition characterized by a brownish yellow pigmentation of the skin and of the sclera of the eye.

•

Icotest - The test used to detect the destruction of old Red Blood Cells (RBC) in the urine.

• •

glucose - normally negative (absent)

•

Hemoglobin Test - Hemolysis in the blood vessels, a rupture in the capillaries of the glomerulus, or hemorrhage in the urinary system may cause hemoglobin to appear in your urine.

• • •

Benedict's Test - Although glucose is easily filtered in the glomerulus, it is not present in the urine because all of the glucose that is filtered is normally reabsorbed from the renal tubules back into the blood.

A chest x-ray is typically the first imaging test used to help diagnose symptoms such as:

• • • •

shortness of breath. a bad or persistent cough. chest pain or injury. fever.

Physicians use the examination to help diagnose or monitor treatment for conditions such as:

• • • • •

pneumonia. heart failure and other heart problems. emphysema. lung cancer. other medical conditions. top of page

How should I prepare? A chest x-ray requires no special preparation. You may be asked to remove some or all of your clothes and to wear a gown during the exam. You may also be asked to remove jewelry, eye glasses and any metal objects or clothing that might interfere with the x-ray images. Women should always inform their physician or x-ray technologist if there is any possibility that they are pregnant. Many imaging tests are not performed during pregnancy so as not to expose the fetus to radiation. If an x-ray is necessary, precautions will be taken to minimize radiation exposure to the baby. The equipment typically used for chest x-rays consists of a wall-mounted, box-like apparatus containing the x-ray film or a special plate that records the image digitally and an x-ray producing tube, that is usually positioned about six feet away. The equipment may also be arranged with the x-ray tube suspended over a table on which the patient lies. A drawer under the table holds the x-ray film or digital recording plate.

RBC number

A portable x-ray machine is a compact apparatus that can be taken to the patient in a hospital bed or the emergency room. The x-ray tube is connected to a flexible arm that is extended over the patient while an x-ray film holder or image recording plate is placed beneath the patient.

WBC number

How does the procedure work?

hCG - normally absent, this hormone appears in the urine of pregnant women. Home pregnancy tests commonly detect this substance.

X-rays are a form of radiation like light or radio waves. X-rays pass through most objects, including the body. Once it is carefully aimed at the part of the body being examined, an x-ray machine produces a small burst of radiation that passes through the body, recording an image on photographic film or a special digital image recording plate.

Microscopic examination A urine sample is about to be examined under a phase-contrast microscope using a Neubauer counting chamber. The urine is under the cover slide, in the upper segment formed by the H-shaped grooves. The numbers and types of cells and/or material such as urinary casts can yield a great detail of information and may suggest a specific diagnosis.

Different parts of the body absorb the x-rays in varying degrees. Dense bone absorbs much of the radiation while soft tissue, such as muscle, fat and organs, allow more of the x-rays to pass through them. As a result, bones appear white on the x-ray, soft tissue shows up in shades of gray and air appears black.

•

Hematuria - associated with kidney stones, infections, tumors and other conditions

• •

Pyuria - associated with urinary infections

•

Red blood cell casts - associated with glomerulonephritis, vasculitis, malignant hypertension

•

White blood cell casts - associated with acute interstitial nephritis, exudative glomerulonephritis, severe pyelonephritis

• •

(heme) granular casts - associated with acute tubular necrosis

Typically, two views of the chest are taken, one from the back and the other from the side of the body as the patient stands against the image recording plate. The technologist, an individual specially trained to perform radiology examinations, will position the patient with hands on hips and chest pressed the image plate. For the second view, the patient's side is against the image plate with arms elevated.

crystalluria -- associated with acute urate nephropathy (or "Acute uric acid nephropathy", AUAN)

Patients who cannot stand may be positioned lying down on a table for chest x-rays.

•

calcium oxalate - associated with ethylene glycol toxicity

eosinophiluria - associated with allergic interstitial nephritis, atheroembolic disease

What is a Chest X-ray (Chest Radiography)? The chest x-ray is the most commonly performed diagnostic x-ray examination. A chest x-ray makes images of the heart, lungs, airways, blood vessels and the bones of the spine and chest. An x-ray (radiograph) is a noninvasive medical test that helps physicians diagnose and treat medical conditions. Imaging with x-rays involves exposing a part of the body to a small dose of ionizing radiation to produce pictures of the inside of the body. X-rays are the oldest and most frequently used form of medical imaging. What are some common uses of the procedure? The chest x-ray is performed to evaluate the lungs, heart and chest wall.

On a chest x-ray, the ribs and spine will absorb much of the radiation and appear white or light gray on the image. Lung tissue absorbs little radiation and will appear dark on the image. Until recently, x-ray images were maintained as hard film copy (much like a photographic negative). Today, most images are digital files that are stored electronically. These stored images are easily accessible and are sometimes compared to current x-ray images for diagnosis and disease management.

You must hold very still and may be asked to keep from breathing for a few seconds while the x-ray picture is taken to reduce the possibility of a blurred image. The technologist will walk behind a wall or into the next room to activate the x-ray machine. When the examination is complete, you will be asked to wait until the radiologist determines that all the necessary images have been obtained. The chest x-ray examination is usually completed within 15 minutes. Additional views may be required within hours, days or months to evaluate any changes in the chest. What will I experience during and after the procedure? A chest x-ray examination itself is a painless procedure. You may experience discomfort from the cool temperature in the examination room and the coldness of the recording plate. Individuals with arthritis or injuries to the chest wall, shoulders or arms may have discomfort trying to

stay still during the examination. The technologist will assist you in finding the most comfortable position possible that still ensures diagnostic image quality.

the P wave on the ECG.

QRS complex

The QRS complex is a recording of a single heartbeat on the ECG that corresponds to the depolarization of the right and left ventricles.

PR interval

The PR interval is measured It is usually from the beginning of the P 120 to 200 ms wave to the beginning of long. the QRS complex.

ST segment

It has a The ST segment connects duration of the QRS complex and the T 0.08 to 0.12 wave. sec (80 to 120 ms).

T wave

The T wave represents the repolarization (or recovery) of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the absolute refractory period. The last half of the T wave is referred to as the relative refractory period (or vulnerable period).

Who interprets the results and how do I get them? A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a signed report to your primary care or referring physician, who will discuss the results with you. The results of a chest x-ray can be available almost immediately for review by your physician. What are the benefits vs. risks? Benefits •

No radiation remains in a patient's body after an xray examination.

•

X-rays usually have no side effects in the diagnostic range.

•

X-ray equipment is relatively inexpensive and widely available in emergency rooms, physician offices, ambulatory care centers, nursing homes and other locations, making it convenient for both patients and physicians.

•

Because x-ray imaging is fast and easy, it is particularly useful in emergency diagnosis and treatment.

Risks •

There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.

•

The chest x-ray is one of the lowest radiation exposure medical examinations performed today. The effective radiation dose from this procedure is about 0.1 mSv, which is about the same as the average person receives from background radiation in 10 days. See the Safety page for more information about radiation dose.

•

QT interval

Women should always inform their physician or x-ray technologist if there is any possibility that they are pregnant. See the Safety page for more information about pregnancy and x-rays.

needed]

The U wave is not always seen. It is typically small, and, by definition, follows the T wave.

U wave Electrocardiography Electrocardiography (ECG or EKG) is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes. [1] It is a noninvasive recording produced by an electrocardiographic device. The etymology of the word is derived from electro, because it is related to electrical activity, cardio, Greek for heart, and graph, a Greek root meaning "to write". Electrical impulses in the heart originate in the sinoatrial node and travel through the intrinsic conducting system to the heart muscle.The impulses stimulate the myocardial muscle fibres to contract and thus induce systole. The electrical waves can be measured at selectively placed electrodes (electrical contacts) on the skin. Electrodes on different sides of the heart measure the activity of different parts of the heart muscle. An ECG displays the voltage between pairs of these electrodes, and the muscle activity that they measure, from different directions, also understood as vectors. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle. It is the best way to measure and diagnose abnormal rhythms of the heart,[2] particularly abnormal rhythms caused by damage to the conductive tissue that carries electrical signals, or abnormal rhythms caused by levels of dissolved salts (electrolytes), such as potassium, that are too high or low.[3] In myocardial infarction (MI), the ECG can identify damaged heart muscle. But it can only identify damage to muscle in certain areas, so it can't rule out damage in other areas.[4] The ECG cannot reliably measure the pumping ability of the heart; for which ultrasound-based (echocardiography) or nuclear medicine tests are used. Waves and intervals A typical ECG tracing of a normal heartbeat (or cardiac cycle) consists of a P wave, a QRS complex and a T wave.[23] A small U wave is normally visible in 50 to 75% of ECGs. The baseline voltage of the electrocardiogram is known as the isoelectric line. Typically the isoelectric line is measured as the portion of the tracing following the T wave and preceding the next P wave. P wave During normal atrial (electrocardiograp depolarization, the main hy) electrical vector is directed from the SA node towards the AV node, and spreads from the right atrium to the left atrium. This turns into

Normal values for the QT The QT interval is measured interval are from the beginning of the between 0.30 QRS complex to the end of and 0.44 the T wave. seconds.[citation

The four deflections were originally named ABCDE but renamed PQRST after correction for artifacts introduced by early amplifiers. Community-acquired pneumonia (CAP) is a disease in which individuals who have not recently been hospitalized develop an infection of the lungs (pneumonia). CAP is a common illness and can affect people of all ages. CAP often causes problems like difficulty in breathing, fever, chest pains, and a cough. CAP occurs because the areas of the lung which absorb oxygen (alveoli) from the atmosphere become filled with fluid and cannot work effectively. CAP occurs throughout the world and is a leading cause of illness and death. Causes of CAP include bacteria, viruses, fungi, and parasites. CAP can be diagnosed by symptoms and physical examination alone, though x-rays, examination of the sputum, and other tests are often used. Individuals with CAP sometimes require treatment in a hospital. CAP is primarily treated with antibiotic medication. Some forms of CAP can be prevented by vaccination. Symptoms Symptoms of CAP commonly include:

• • •

problems breathing

•

sharp or stabbing chest pain

•

rapid, shallow breathing that is often painful

coughing that produces greenish or yellow sputum a high fever that may be accompanied with sweating, chills, and uncontrollable shaking

Less common symptoms include:

• • •

the coughing up of blood (hemoptysis)

•

excessive fatigue

• •

blueness of the skin (cyanosis)

headaches (including migraine headaches) loss of appetite

nausea

• • • •

vomiting

•

Bacteria and fungi also typically enter the lung with inhalation, though they can reach the lung through the bloodstream if other parts of the body are infected. Often, bacteria live in parts of the upper respiratory tract and are constantly being inhaled into the alveoli. Once inside the alveoli, bacteria and fungi travel into the spaces between the cells and also between adjacent alveoli through connecting pores. This invasion triggers the immune system to respond by sending white blood cells responsible for attacking microorganisms (neutrophils) to the lungs. The neutrophils engulf and kill the offending organisms but also release cytokines which result in a general activation of the immune system. This results in the fever, chills, and fatigue common in CAP. The neutrophils, bacteria, and fluid leaked from surrounding blood vessels fill the alveoli and result in impaired oxygen transportation. Bacteria often travel from the lung into the blood stream and can result in serious illness such as septic shock, in which there is low blood pressure leading to damage in multiple parts of the body including the brain, kidney, and heart.

diarrhea joint pain (arthralgia) muscle aches (myalgia)

The manifestations of pneumonia, like those for many conditions, might not be typical in older people. They might instead experience: •

new or worsening confusion

•

hypothermia

•

falls*

Additional symptoms for infants could include: •

being overly sleepy

• •

yellowing of the skin (jaundice) difficulties feeding[2]

Diagnosis Individuals with symptoms of CAP require further evaluation. Physical examination by a health provider may reveal fever, an increased respiratory rate (tachypnea), low blood pressure (hypotension), a fast heart rate (tachycardia), and/or changes in the amount of oxygen in the blood. Feeling the way the chest expands (palpation) and tapping the chest wall (percussion) to identify dull areas which do not resonate can identify areas of the lung which are stiff and full of fluid (consolidated). Examination of the lungs with the aid of a stethoscope can reveal several things. A lack of normal breath sounds or the presence of crackling sounds (rales) when the lungs are listened to (auscultated) can also indicate consolidation. Increased vibration of the chest when speaking (tactile fremitus) and increased volume of whispered speech during auscultation of the chest can also reveal consolidation X-rays of the chest, examination of the blood and sputum for infectious microorganisms, and blood tests are commonly used to diagnose individuals with suspected CAP based upon symptoms and physical examination. The use of each test depends on the severity of illness, local practices, and the concern for any complications resulting from the infection. All patients with CAP should have the amount of oxygen in their blood monitored with a machine called a pulse oximeter. This helps determine how well the lungs are able to work despite infection. In some cases, analysis of arterial blood gas may be required to accurately determine the amount of oxygen in the blood. Complete blood count (CBC), a blood test, may reveal extra white blood cells, indicating an infection. Chest x-rays and chest computed tomography (CT) can reveal areas of opacity (seen as white) which represent consolidation. A normal chest x-ray makes CAP less likely; however, CAP is sometimes not seen on x-rays because the disease is either in its initial stages or involves a part of the lung not easily seen by x-ray. In some cases, chest CT can reveal a CAP which is not present on chest x-ray. X-rays can often be misleading, as many other diseases can mimic CAP such as heart problems or other types of lung damage.[4] Several tests can be performed to identify the cause of an individual's CAP. Blood cultures can be drawn to isolate any bacteria or fungi in the blood stream. Sputum Gram's stain and culture can also reveal the causative microorganism. In more severe cases, a procedure wherein a flexible scope is passed through the mouth into the lungs (bronchoscopy) can be used collect fluid for culture. Special tests can be performed if an uncommon microorganism is suspected (such as testing the urine for Legionella antigen when Legionnaires' disease is a concern). Pathophysiology The symptoms of CAP are the result of both the invasion of the lungs by microorganisms and the immune system's response to the infection. The mechanisms of infection are quite different for viruses and the other microorganisms.

•

Viruses Viruses must invade cells in order to reproduce. Typically, a virus will reach the lungs by traveling in droplets through the mouth and nose with inhalation. There, the virus invades the cells lining the airways and the alveoli. This invasion often leads to cell death either through direct killing by the virus or by self-destruction through apoptosis. Further damage to the lungs occurs when the immune system responds to the infection. White blood cells, in particular lymphocytes, are responsible for activating a variety of chemicals (cytokines) which cause leaking of fluid into the alveoli. The combination of cellular destruction and fluid-filled alveoli interrupts the transportation of oxygen into the bloodstream. In addition to the effects on the lungs, many viruses affect other organs and can lead to illness affecting many different bodily functions. Viruses also make the body more susceptible to bacterial infection; for this reason, bacterial pneumonia often complicates viral CAP.

Bacteria and fungi

•

Parasites There are a variety of parasites which can affect the lungs. In general, these parasites enter the body through the skin or by being swallowed. Once inside the body, these parasites travel to the lungs, most often through the blood. There, a similar combination of cellular destruction and immune response causes disruption of oxygen transportation.

Microorganisms causing CAP There are over a hundred microorganisms which can cause CAP. The most common types of microorganisms are different among different groups of people. Newborn infants, children, and adults are at risk for different spectrums of disease causing microorganisms. In addition, adults with chronic illnesses, who live in certain parts of the world, who reside in nursing homes, who have recently been treated with antibiotics, or who are alcoholics are at risk for unique infections. Even when aggressive measures are taken, a definite cause for pneumonia is only identified in half the cases. Infants Newborn infants can acquire lung infections prior to being born either by breathing infected amniotic fluid or by blood-borne infection across the placenta. Infants can also inhale (aspirate) fluid from the birth canal as they are being born. The most important infection in newborns is caused by Streptococcus agalactiae, also known as Group B Streptococcus or GBS. GBS causes at least 50% of cases of CAP in the first week of life.[5] Other bacterial causes in the newborn period include Listeria monocytogenes and tuberculosis. Viruses can also be transferred from mother to child; herpes simplex virus is the most common and life-threatening, but adenovirus, mumps, and enterovirus can also cause disease. CAP in older infants reflects increased exposure to microorganisms. Common bacterial causes include Streptococcus pneumoniae, Escherichia coli, Klebsiella pneumoniae, Moraxella catarrhalis, and Staphylococcus aureus. A unique cause of CAP in this group is Chlamydia trachomatis, which is acquired during birth but which does not cause pneumonia until 2–4 weeks later. Common viruses include respiratory syncytial virus (RSV), metapneumovirus, adenovirus, parainfluenza, influenza, and rhinovirus. RSV in particular is a common source of illness and hospitalization.[6] Fungi and parasites are not typically encountered in otherwise healthy infants, though maternally-derived syphilis can be a cause of CAP in this age group. Children For the most part, children older than one month of life are at risk for the same microorganisms as adults. However, children less than five years are much less likely to have pneumonia caused by Mycoplasma pneumoniae, Chlamydophila pneumoniae, or Legionella pneumophila. In contrast, older children and teenagers are more likely to acquire Mycoplasma pneumoniae and Chlamydophila pneumoniae than adults.[7] Adults The full spectrum of microorganisms are responsible for CAP in adults. Several important groups of organisms are more common among people with certain risk factors. Identifying people at risk for these organisms is important for appropriate treatment.

•

Viruses Viruses cause 20% of CAP cases. The most common viruses are influenza, parainfluenza, respiratory syncytial virus, metapneumovirus, and adenovirus. Less common viruses causing significant illness include chicken pox, SARS, avian flu, and hantavirus. [8]

•

Atypical organisms The most common bacterial causes of pneumonia are the so-called atypical bacteria Mycoplasma pneumoniae and Chlamydophila pneumoniae. Legionella pneumophila is considered atypical but is less common. Atypical organisms are more difficult to grow, respond to different antibiotics, and were discovered more recently than the typical bacteria discovered in the early twentieth century.

•

Streptococcus pneumoniae Streptococcus pneumoniae is a common bacterial cause of CAP. Prior to the development of antibiotics and vaccination, it was a leading cause of death. Traditionally highly sensitive to penicillin, during the 1970s resistance to multiple antibiotics began to develop. Current strains of "drug resistant Streptococcus pneumoniae" or DRSP are common, accounting for twenty percent of all Streptococcus pneumoniae infections. Adults with risk factors for DRSP including being older than 65, having exposure to children in day care, having alcoholism or other severe underlying disease, or recent treatment with antibiotics should initially be treated with antibiotics effective against DRSP.[9]

•

Treatment of CAP in children depends on both the age of the child and the severity of his/her illness. Children less than five do not typically receive treatment to cover atypical bacteria. If a child does not need to be hospitalized, amoxicillin for seven days is a common treatment. However, with increasing prevalence of DRSP, other agents such as cefpodoxime will most likely become more popular in the future.[11] Hospitalized children should receive intravenous ampicillin, ceftriaxone, or cefotaxime. Adults In 2001, the American Thoracic Society, drawing on work by the British and Canadian Thoracic Societies, established guidelines for the management of adults with CAP which divided individuals with CAP into four categories based upon common organisms encountered.[12]

•

This group, the largest, is composed of otherwise healthy patients without risk factors for DRSP, enteric Gram negative bacteria, Pseudomonas, or other less common causes of CAP. The primary microoganisms in this group are viruses, atypical bacteria, penicillin sensitive Streptococcus pneumoniae, and Hemophilus influenzae. Recommended management is with a macrolide antibiotic such as azithromycin or clarithromycin for seven[1] to ten days.

•

Hemophilus influenzae

Enteric Gram negative bacteria The enteric Gram negative bacteria such as Escherichia coli and Klebsiella pneumoniae are a group of bacteria that typically live in the human intestines. Adults with risk factors for infection including residence in a nursing home, serious heart and lung disease, and recent antibiotic use should initially be treated with antibiotics effective against Enteric Gram negative bacteria.

•

Pseudomonas aeruginosa Pseudomonas aeruginosa is an uncommon cause of CAP but is a particularly difficult bacteria to treat. Individuals who are malnourished, have a lung disease called bronchiectasis, are on corticosteroids, or have recently had strong antibiotics for a week or more should initially be treated with antibiotics effective against Pseudomonas aeruginosa.[10]

Many less common organisms cause CAP. They are typically identified because an individual has special risk factors or after treatment for the common causes has failed. These rarer causes are covered in more detail in their specific pages: bacterial pneumonia, viral pneumonia, fungal pneumonia, and parasitic pneumonia. Treatment CAP is treated by administering an antibiotic which is effective in killing the offending microorganism as well as managing any complications of the infection. If the causative microorganism is unidentified, different antibiotics are tested in the laboratory in order to identify which medication will be most effective. Often, however, no microorganism is ever identified. Also, since laboratory testing can take several days, there is some delay until an organism is identified. In both cases, a person's risk factors for different organisms must be remembered when choosing the initial antibiotics (called empiric therapy). Additional consideration must be given to the setting in which the individual will be treated. Most people will be fully treated after taking oral pills while other people need to be hospitalized for intravenous antibiotics and, possibly, intensive care. In general, all therapies in older children and adults will include treatment for atypical bacteria. Typically this is a macrolide antibiotic such as azithromycin or clarithromycin although a fluoroquinolone such as levofloxacin can substitute. Doxycycline is now the antibiotic of choice in the UK for complete coverage of the atypical bacteria. This is due to increased levels of clostridium difficile seen in hospital patients being linked to the increased use of clarithromycin. [edit] Newborn infants Most newborn infants with CAP are hospitalized and given intravenous ampicillin and gentamicin for at least ten days. This treats the common bacteria Streptococcus agalactiae, Listeria monocytogenes, and Escherichia coli. If herpes simplex virus is the cause, intravenous acyclovir is administered for 21 days. Children

Hospitalized individuals not at risk for Pseudomonas This group requires hospitalization and administration of intravenous antibiotics. Treatment is with either an intravenous fluoroquinolone active against Streptococcus pneumoniae such as levofloxacin or beta-lactam antibiotic such as cefotaxime, ceftriaxone, ampicillin/sulbactam, or high-dose ampicillin plus an intravenous macrolide antibiotic such as azithromycin or clarithromycin for seven to ten days.

Hemophilus influenzae is another common bacterial cause of CAP. First discovered in 1892, it was initially believed to be the cause of influenza because it commonly causes CAP in people who have suffered recent lung damage from viral pneumonia.

•

Healthy outpatients without risk factors

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Individuals requiring intensive care at risk for Pseudomonas Individuals being treated in an intensive care unit with risk factors for infection with Pseudomonas aeruginosa require specific antibiotics targeting this difficult to eradicate bacteria. One possible regimen is an intravenous antipseudomonal beta-lactam such as cefepime, imipenem, meropenem, or piperacillin/tazobactam plus an intravenous antipseudomonal fluoroquinolone such as levofloxacin. Another recommended regimen is an intravenous antipseudomonal beta-lactam such as cefepime, imipenem, meropenem, or piperacillin/ tazobactam plus an intravenous aminoglycoside such as gentamicin or tobramycin plus either an intravenous macrolide such azithromycin or an intravenous nonpseudomonal fluoroquinolone such as ciprofloxacin.

The decision to hospitalize Some people with CAP require hospitalization and more intensive care than the majority. In general, a discussion between the individual and his or her health care provider determines the need for hospitalization. Clinical prediction rules, such as the pneumonia severity index and CURB-65 have been developed to help guide the decision.[13] Factors which increase the need for hospitalization include age greater than 65; underlying chronic illnesses; a respiratory rate greater than thirty breaths per minute; a systolic blood pressure less than 90 mmHg; a heart rate greater than 125 per minute; temperature less than 35 or greater than 40°C; confusion; and evidence of infection outside the lung. Laboratory results which increase the need for hospitalization include arterial oxygen tension less than 60 mm Hg, carbon dioxide of greater than 50 mmHg, or pH less than 7.35 while breathing room air; hematocrit less than 30%; creatinine greater than 1.2 mg/dl or blood urea nitrogen greater than 20 mg/ dl; white blood cell count less than 4 × 10^9/L or greater than 30 × 10^9/L; and absolute neutrophil count less than 1 x 10^9/L. X-ray findings which increase the need for hospitalization include involvement of more than one lobe of the lung, presence of a cavity, and the presence of a pleural effusion. Prognosis Individuals who are treated for CAP outside of the hospital have a mortality rate less than 1%. Fever typically responds in the first two days of therapy and other symptoms resolve in the first week. The x-ray, however, may remain abnormal for at least a month, even when CAP has been successfully treated. Among individuals who require hospitalization, the mortality rate averages 12% overall, but is as much as 40% in people who have bloodstream infections or require intensive care.[14] Factors which increase mortality are the same as those which increase the need for hospitalization and are listed above. When CAP does not respond as expected, there are several possible causes. A complication of CAP may have occurred or a previously unknown health problem may be playing a role. Both situations are covered in more detail below. Additional causes include inappropriate antibiotics for the causative

organism (ie DRSP), a previously unsuspected microorganism (such as tuberculosis), or a condition which mimics CAP (such as Wegener's granulomatosis). Additional testing may be performed and may include additional radiologic imaging (such as a computed tomography scan) or a procedure such as a bronchoscopy or lung biopsy.