Epidemiology of nasopharyngeal colonization with nontypeable Haemophilus influenzae in the first two years of life.

A total of 200 children were followed from birth through 2 years of age with nasopharyngeal (NP) cultures to determine the normal colonization pattern of nontypeable H. influenzae (NTHI) in young children. NP cultures were obtained routinely at 13 scheduled visits. 44% of children became colonized by 2 years; acquisition was greatest in the first year. Colonization with the initial strain, as determined by outer membrane proteins, persisted from 1-5 months, median 2 months. Children carried one predominant strain at a time but became colonized with up to 7 different strains, mean 2.2, over 2 years. Three patterns of colonization were observed: i) rapid elimination of the initial strain, ii) prolonged colonization with the initial strain, and iii) colonization with different strains. Reacquisition of a previously carried strain was rare. Changes in outer membrane protein patterns reflected acquisition of new strains rather than phenotypic changes of old strains. Children colonized with 1 strain for < or = 2 months generated a greater mucosal antibody response, log 2.35, U/ng/ml SIgA, than children colonized with different strains, log 1.89, U/ng/ml SIgA, p <0.01. These data suggest that duration of colonization with one strain and the acquisition of a new strain is regulated by the local specific SIgA.