Outbreak of Haemophilus influenzae type b meningitis in a day care center

Three cases of Haemophilus influenzae type b (Hib) meningitis in a Swedish day care center prompted the investigation of the nasopharyngeal carriage in attendees of that day care center (I), and among children in another day center (II) in the same city, but without meningitis cases. Because the evaluation of the spread of Haemophilus influenzae (Hi) isolates through a population, such as children in day care centers, requires stable identification markers for the bacteria, this study used multilocus enzyme electrophoresis to separate Hib carried by day care attendees from the disease-associated Hib clone. The three meningitis episodes were caused by the same clone of Hib (ET14). This and other Hib clones occurred in the healthy carriers. The frequency of H. influenzae carriage and composition of the H. influenzae flora differed between the two day care centers. Center I with the meningitis cases had a lower overall frequency of H. influenzae carriage, 11 of 40 (28%) compared with both the control day care center (57%) and previous studies. The main difference between the two day care centers was in the nontypable H. influenzae (HiNT) flora. The frequency of HiNT was higher in the center without Hib disease, and there was a higher degree of sharing of HiNT isolates among the children in Center II. This raised the question of an inverse relationship between carriage of HiNT and Hib infection. The results emphasized the importance of accurate identification of the disease isolate in order to estimate the risk of acquisition and dissemination to secondary cases.