Haemophilus influenzae
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Bacteria - Gram Negative
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Haemophilus influenzae
- Note: contrast vs. haemophilus ducreyi (produces genital ulcers)
- Many different strains of H. influenzae exist
- Serotype type B (Hib) is the most pathogenic
- Characteristics
- Gram negative
- Coccobacilli or bacilli
- Facultative Anaerobe
- Oxidase +
- Non-motile
- Requires factors V (NAD+) and X (hematin) for growth on chocolate agar
- Can also be grown with S aureus, which provides factor V via RBC hemolysis
- Virulence factors
- Produces IgA protease
- Polysaccharide capsule
- capsule composed of polyribosylribitol phosphate (PRP)
- Asplenic patients (past surgery, sickle cell), people with C1 complement deficiency, or people with B-cell immunodeficiencies (e.g. Bruton’s agammaglobulinemia) are particularly susceptible to severe infections by encapsulated organisms
- Presentation
- Important: H. influenzae does not cause the flu (Influenza virus causes the flu)
- Aerosol transmission
- Respiratory/airway infections
- Otitis media/sinusitis
- Pneumonia/bronchitis
- Caused by non-serotypable H. influenzae
- Conjunctivitis
- Meningitis
- Caused by H. influenzae type B (Hib)
- Hib may also cause epiglottitis
- Can produce culture-negative endocarditis
- Part of the HACEK organisms (Haemophilus, Actinobacillus, Cardiobacter, Eikenella, Kingella)
- Treatment
- Amoxicillin (with clavulanate)
- First-line for mucosal infections (sinusitis, otitis media)
- Ceftriaxone
- First-line for meningitis
- Rifampin prophylaxis for close contacts
- Amoxicillin (with clavulanate)
- Prophylaxis
- Haemophilus influenza type b (Hib) vaccine
- contains bacterial capsular polysaccharide conjugated with diphtheria toxoid, which improves immunogenicity
- given between 2 and 18 months of age
- Haemophilus influenza type b (Hib) vaccine