Lecture 38 - Haemophilus - 4 Nov 2006

Haemophilus 4th Year

Objectives At the end of this lecture the students should have learnt and be able to:  Describe the characteristics of the organism  Recall the pathogenesis  Recall the infections and clinical features  Regurgitate the laboratory diagnosis  Recall the treatment and prevention

Haemophili of medical importance 

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H. influenzae - major pathogen, associated with meningitis, epiglottitis, pneumonia, septic arthritis, bronchitis and otitis media H. aegypticus – epidemic conjunctivitis H. ducreyi - chancroid H. parainfluenzae H. aphrophilus H. paraaphrophilus 

Infective endocarditis, dental infections,

Morphology 

Pleomorphic Gram-negative rods

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In clinical specimens – small, uniform coccobacillus

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In cultures – longer, filamentous rods

Growth factors  

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All require blood for growth Requirement based on “X” and “V” factors X factor – haemin V factor – nicotinamide adenine dinucleotide (NAD) or phosphate (NADP) Haemophili – catalase-positive, oxidase positive and ferment glucose

Growth on laboratory media  

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Chocolate agar – X & V factors Horse or Rabbit Blood Agar – X & V factors Ordinary Blood Agar – contains low level of V factor S. aureus – excrete V factor  Growth around S. aureus colonies – “Satellitism” 

Pathogenesis H. influenzae  

Exclusively human pathogen Resides in the URT Non-capsulated strains - nasopharynx in 2580%  Capsulated strains (a-f)- in 5-10%  Capsular type b – in 1-5% 

Invasive infections       

Usually caused by capsular type b Meningitis Epiglottitis Bacteraemia Septic arthritis Pneumonia Cellulitis Occur in children 2 months to 5 years  Most cases < 2 years of age  Polysaccharide capsule – major virulence factor 

Non-invasive diseases   

Otitis media Sinusitis Purulent episodes of exacerbations of chronic obstructive airway disease Usually initiated by viral infections  Non-capsulated strains are usually responsible 

Laboratory diagnosis   

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H. influenzae requires X and V factors Grows on Chocolate agar Satellitism around S. aureus on Blood agar Blood culture Detection of type b polysaccharide antigen in body fluid CIE  Latex agglutination 

Treatment     

Cefuroxime, Cefotaxime, Ceftriaxone Amoxicillin-clavulanic acid Chloramphenicol Ciprofloxacin Azithromycin, Clarithromycin

Control Active immunization  Purified type b capsular polysaccharide vaccine 

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Poorly immunogenic in children < 2 years

Conjugate vaccine 

Polysaccharide covalently coupled to tetanus toxoid, Neisseria meningitidis outer-membrane protein, diphtheria

Control Prophylaxis     

Rifampicin 20 mg/kg (600 mg max) orally od for 4 days Eradicating carriage Prevent secondary infection in both household and nursery contacts Unvaccinated siblings > 4 years conjugate Hib vaccine Unvaccinated siblings < 4 years – chemoprophylaxis and vaccine

H. Influenzae biogroup aegypticus  

Purulent conjunctivitis Brazilian purpuric fever Recognized in Brazil in 1984  Conjunctivitis proceeds to overwhelming septicaemia  Rx: Ampicillin + chloramphenicol 

H. ducreyi  

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Small Gram-negative bacilli Sexually transmitted disease – chancroid Prevalent in tropical regions, e.g. Africa and Asia Painful penile ulcers – usually soft Inguinal lymphadenitis Rx: Sulphonamides + streptomycin  Tetracycline or erythromycin 

Case presentation A obviously worried mother brought her 2-year old child to the A & E with complaints of gradual onset of irritability, poor feeding, crying and the child constantly touching her ears. Started 4 days ago. Today she appears unable to bend her neck. O/E: the tympanum was red and bulging, To = 40oC, there was neck rigidity.  What are your provisional diagnoses?