Haemophilus influenzae

Abstract

Haemophilus influenzae, a common commensal of the pharynx of humans, is considered part of the normal pharyngeal flora. In addition, it is an important cause of human infections. Strains that possess one of the six polysaccharide capsules, types a through f, cause invasive infections such as bacteremia, meningitis, septic arthritis, epiglottitis, and facial cellulitis, with type b infections being significantly more common (greater than 90%) than types a and c-f. Use of the highly successful type b vaccine, composed of the type b polysaccharide conjugated to one of several protein carriers, has resulted in dramatic reductions in rates of invasive infections in the United States and in many Western countries. Strains with no capsule, the so-called non-typeable strains, are frequent causes of localized infections such as otitis media and sinusitis in children and adults, as well as bronchitis and pneumonia in adults. While the organism lives asymptomatically in the pharynges, it does not cause localized pharyngitis. No vaccine is yet available to protect against infection with non-typeablestrains. © Springer Science+Business Media, LLC 2009.