Bactericidal antibody and susceptibility to otitis media caused by nontypable strains of Haemophilus influenzae.

We have developed a bactericidal antibody assay to determine the role of circulating antibody to nontypable strains of Haemophilus influenzae in children with otitis media. Antibody infecting strain was present in the acute sera of 2/20 children with otitis media caused by H. influenzae NT; 15/18 of these patients had covalescent specimens with titers greater than or equal to 1:2 (X2 = 13.0, P < 0.001). The acute sera of 95 children with otitis media caused by various organisms were screened for bactericidal activity against a randomly selected H. influenzae NT stain. Antibody was present in 0/28 acute sera of patients whose infection was caused by H. influenzae NT and in 18/67 (26.9% of those whose middleear exudates were sterile or contained other bacterial species (X2 = 9.95, P < 0.01). A bactericidal antibody response generally follows infection of the middlw ear with H. influenzae NT. The absence of antibody to a single strain in the sera of some children appears to be associated with susceptibility to this infection.