Lecture 41 - Legion Ella - 8 Nov 2006

LEGIONELLA

Objectives At the end of this lecture the students should be able to:  Recall the general characteristics of Legionella  Recall the clinical features  Understand the epidemiology of the disease  Enumerate the treatment and prevention strategies

Species  39

spp.; 18 are associated with human diseases

 Legionella

pneumophila. - 3 subspecies L. pneumophila serogroup 1 (SG1)

General characteristics  Thin,

pleomorphic GNB or coccobacilli  Conventional stains and silver stain  Produces catalase and β-lactamase  Fastidious  No person-to-person transmission

Pathogenicity  Facultative

intracellular organism  Survives and multiplies inside the phagocytes  Adhesion – OMPs – mediates adhesion and penetration  Haemolysin, cytotoxin and endotoxin  ? tissue damage

Clinical diseases 1. 2. 

Legionnaires’ disease Pontiac fever Incubation period: 2 –10 days

Legionnaires’ disease  Pneumonia; patchy and diffuse or lobar  Extrapulmonary: hepato- and splenomegaly  Alveolar inflammatory exudates containing neutrophils and macrophages

Clinical signs:  Fever;

>90%, chills, headache and cough (>75%)  Cough non-productive or non-purulent sputum.  Atypical pneumonia  Watery diarrhoea – 30-50% of patients  Changes in mental status – disorientation, confusion, sometimes focal neurological signs

Pontiac fever  Flu-like

syndrome without lung involvement  Self-limiting disease.  Carries good prognosis  Highly contagious

Epidemiology  Transmission  Inhalation  Source

– Warm water sources;

– Ponds in cooling towers of refrigerated plants

in air-conditioning systems – Hot water systems in hotels and hospitals – Whirlpool spa baths – Shower heads and faucets  No

person-to-person transmission

Predisposing factors, Incidence, Mortality rates  Immunosuppression  Decrease

in local defenses e.g. chronic lung, smoking, aging (elderly)

 Affects

>40 years old; peak at 60-70 years  20% of the older population is serologically positive  MR

- 15-20% despite adequate treatment

Laboratory diagnosis  Sputum,

bronchial aspirates or washings.  Biopsy materials, urine, serum  Silver stain or DFA of biopsy tissue or sputum  BCYE medium – colonies “cut-glass” appearance  DNA probe – fast: detects whole organism  PCR – very useful  Antigen detection tests  ELISA – soluble antigen in urine

Treatment, Prevention.  Drug

of choice – Erythromycin,  Rifampicin; extremely active  Ciprofloxacin; active in-vitro but not as others in-vivo. Prevention  There is no vaccine.  Identify environmental source  Take adequate measures.

Case presentation A 60-year old Kuwaiti man who recently returned from a holiday to Spain, C/O headache, fever, non-productive cough and diarrhoea of 2 days duration. O/E: He was disorientated, febrile (To=40oC). His CXR shows patchy and diffuse pneumonic changes in both lung fields.    

What is your diagnosis? Name 3 possible pathogens What microbiological tests should be performed to establish a diagnosis? How would you treat such a case?