Epidemiology and prevention of respiratory tract infections due to nonencapsulated Haemophilus influenzae.

Abstract

Nonencapsulated Haemophilus influenzae cause mainly respiratory tract infections, including otitis, sinusitis, and pneumonia. These infections may become chronic or recurrent in patients with bronchitis or otitis. Patients are usually infected with one strain at a time. During recurrent otitis, H. influenzae isolates have an outer membrane protein composition different from that seen during earlier episodes. In chronic bronchitis, H. influenzae strains persist for up to 1 year. In addition, isolates with different outer membrane protein compositions have been obtained that are antigenic variants of previous isolates. The variations occur in outer membrane protein b,c (P2), d (P5), or both. The variable parts are immunodominant, and antibodies to these parts are bactericidal. Cross-reactive bactericidal antibodies to outer membrane proteins have been elicited in immunized animals. These data indicate that natural immunity to nonencapsulated H. influenzae is mainly strain-specific but also that biologically active cross-reactive antibodies can be elicited by immunization.