Ampicillin-resistant Haemophilus in the oropharynx: prevalence in three groups of young, middle-class children.

Infections caused by ampicillin-resistant Haemophilus influenzae type b are prevalent in Fairfax County, VA. In order to gain information on pharyngeal carriage of ampicillin-resistant H influenzae, oropharyngeal cultures were obtained from 249 young children. The study population comprised three groups: 90 healthy children (group A), 79 children who had finished a ten-day course of amoxicillin treatment for acute otitis media (group B), and 80 children who were brought to our office for treatment of purulent nasopharyngitis (group C). Approximately 60% of the children in each group carried Haemophilus in the oropharynx. H parainfluenzae was the predominant oropharyngeal species in group 1. H influenzae was predominant in the other two groups. Ampicillin-resistant Haemophilus sp organisms were recovered from 16% of children in group A, 25% of those in group B, and 17% of patients in group C. Recent exposure to ampicillin was associated with an increase in the recovery of ampicillin-resistant strains of Haemophilus.