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Haemophilus influenzae on chocolate agar. Cultivated 24 hours in an aerobic
atmosphere enriched with 5% carbon dioxide, 37°C.
H. influenzae was mistakenly considered to be the cause of influenza until 1933, when the viral etiology of the flu became apparent.
Most strains of H. influenzae are opportunistic pathogens; that is, they usually live in their host without causing disease, but cause problems only when other factors (such as a viral infection or reduced immune function) create an opportunity.
In infants and young children, H. influenzae type b (Hib) causes bacteremia, pneumonia, and acute bacterial meningitis. On occasion, it causes cellulitis, osteomyelitis, epiglottitis, and infectious arthritis. Hib remains a major cause of lower
respiratory tract infections in infants and children in developing countries where the vaccine is not widely used.
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