Clonal spread of an invasive strain of Haemophilus influenzae type b among nursery contacts accompanied by a high carriage rate of non-disease-associated strains.

Haemophilus influenza carriage was examined in unvaccinated nursery contacts of a patient with H. influenzae type b (Hib) meningitis and isolates were typed by pulsed-field gel electrophoresis (PFGE). Nasopharyngeal isolates were classified into eight PFGE patterns. Seven Hib carriers were found among 15 nursery contacts. The isolates from the carriers showed a PFGE pattern identical to that of the meningitis strain. The carrier rate of non-disease-associated strains was also high (47%, 7 of 15). This study suggests that the clonal spread of invasive (serotype b) H. influenzae strains is accompanied by a high carriage rate of non-disease-associated strains.