Otitis media in children. I. The systemic immune response to nontypable Hemophilus influenzae.

Twenty-one infants experienced 29 episodes of otitis media with effusion caused by nontypable Hemophilus influenzae (NTHI) during 2 y of observation. Bactericidal antibody was detected in acute serum of 26% of the subjects at a mean titer of 0.8 +/- 0.3 (log2) and was observed in convalescent serum of all of the individuals at a mean titer of 4.0 +/- 0.3 (log2, P less than .001). The serum bactericidal antibody response was not age-dependent (r = .08, P greater than .05). Serum concentrations of bactericidal antibody remained stable for the entire observation period in 90% of the children. The presence of serum bactericidal antibody correlated significantly with a reduction in the number of bacteria present in the middle ear fluid (P less than .025). Eight children experienced a second episode of otitis media with effusion caused by a different serotype of NTHI. All those who lacked bactericidal antibody against the organism causing the second episode possessed bactericidal antibody against the first strain at the time of the second episode. These data suggest that the immune response to NTHI in otitis media with effusion is type-specific. The occurrence of second episodes of otitis media with effusion due to different strains of NTHI in the face of preexisting heterologous bactericidal antibody suggests a lack of NTHI in the face of preexisting heterologous bactericidal antibody suggests a lack of cross-protection.