Relative proportions of H. influenzae and H. parainfluenzae in the throat and nasopharynx of healthy children

To determine normal proportions of pharyngeal H. influenzae and H. parainfluenzae, qualitative and quantitative mapping of the species in the pharynx of 538 healthy children was carried out. The detection rates of H. influenzae rose to a peak at 4, 5 years, with a slow decline thereafter. In contrast to H. influenzae, the detection rates of H. parainfluenzae rose as the child became older in age. The rates of H. influenzae and H. parainfluenzae of the total cultivable flora showed the same tendency as the detection rates. No consistent seasonal fluctuations was found with H. influenzae. The pharyngeal swab was inferior to the nasopharyngeal swab in each age group, for detecting the carriage of H. influenzae and H. parainfluenzae in the upper respiratory tract. The rate of ampicillin-resistant H. influenzae was 17.7% in the nasopharynx.