Haemophilus influenzae is transmitted by direct contact with respiratory droplets from a nasopharyngeal carrier or an infected patient. Invasive infection of H. influenzae can present as meningitis, bacteremia, septic arthritis, pneumonia, otitis media, conjunctivitis, sinusitis, and acute epiglottis, especially in the very young. These infections, in addition to endocarditis and osteomyelitis, may also occur in adults, although much less commonly. The elderly, very young children, children that attend daycare, and those exposed to patients with an H. influenzae infection, are at highest risk for contracting H. influenzae.
H. influenzae has several serotypes or strains. The bacterium, particularly the virulent strain H. influenzae serotype b (Hib), was once the leading cause of bacterial meningitis in young children in the United States. However, since the 1988 introduction of the Hib conjugate vaccine, the rate of pediatric Hib-related disease in this country has declined by 99%. In developed countries, like the United States, Hib occurs primarily in children who are under-immunized or who are too young to complete the immunization series. In developing countries, where the vaccine is not readily available, Hib disease continues to be a major burden on the young. Additional information about the vaccine can be found on the CDC Hib Vaccine Statement page.
For more information on Haemophilus influenzae, please visit:CDC Hib Disease Website