Possible high rate of transmission of nontypeable Haemophilus influenzae, including beta-lactamase-negative ampicillin-resistant strains, between children and their parents.

The possible transmission of nontypeable Haemophilus influenzae between children and their parents was evaluated in 18 pairs of subjects from 15 families. Of the 33 isolates, 31 were found to be beta-lactamase negative, including 10 beta-lactamase-negative, ampicillin (AMP)-resistant (BLNAR) strains (AMP MIC, >or=1.0 microg/ml) and 2 were beta-lactamase producing. Molecular typing by pulsed-field gel electrophoresis (PFGE) showed that 10 BLNAR isolates had 6 patterns, 23 non-BLNAR isolates had 13 patterns, and these patterns were different from each other, except for 1 pattern. As a result, the PFGE patterns in 14 of 18 pairs were indistinguishable and those in 4 pairs were different. These data indicate a possible high rate of intrafamilial transmission of nontypeable H. influenzae, including BLNAR strains, between children and their parents.