Frequency of ampicillin-resistant Haemophilus parainfluenzae in children.

Ampicillin resistance has been described in Haemophilus species other than Haemophilus influenzae, but its frequency and significance are uncertain. In a throat-culture survey, beta-lactamase-producing Haemophilus parainfluenzae was detected in 192 (72%) of 266 ambulatory children. Ampicillin-resistant H. parainfluenzae was more frequently found in children from three to four years of age (88%) or in those who attended day-care programs (97%) and less frequently in older children and parents (33%). Colonization was unrelated to previous exposure to antibiotics or to a history of otitis media. Colonization with ampicillin-resistant H. parainfluenzae occurred in 88% of subjects with H. influenzae, including all of seven subjects carrying ampicillin-resistant H. influenzae. Colonization with beta-lactamase-producing H. parainfluenzae was 26 times more frequent than with H. influenzae. If the mechanisms and genetics of resistance are the same, H. parainfluenzae may prove to be a vector for spread of resistance genes of H. influenzae.