Nasopharyngeal colonization by Haemophilus influenzae in children living in an orphanage

Aim. To study colonization and transmission of Haemophilus influenzae in a cohort of children <2 years old living in the unique epidemiologic conditio ns of a closed community of an orphanage. Methods. Fifty-three children, ages 0 to 24 months, were followed for 1 yea r. All children >2 months were vaccinated against H. influenzae serotype b. Nasopharyngeal cultures were collected monthly or, in children <6 months o f age, every 2 weeks. Antibiotic susceptibility, serotype, biotype and geno type (pulsed field gel electrophoresis) of each isolate were determined. As control, 39 H. influenzae isolates were recovered from various regions in France. Results. The mean monthly rate of carriage was 45% ranging from 17 to 70%. Most isolates belonged to biotype II (62%), 4 isolates to serotype f (3.6%) and none to serotype b, and 60% of the 111 isolates produced beta-lactamas e. A complete concordance was found among biotype, serotype, pulsotype and antimicrobial susceptibility. On average children were sequentially coloniz ed by 3 different isolates. The mean duration of carriage for a given isola te was similar to1.4 months. In younger children the mean age of primary co lonization was 2 months. Contrasting with the high genetic heterogeneity of 39 control isolates, most isolates (82%) belonged to only 5 pulsotypes. Th ree main H. influenzae clones rapidly spread in the community and colonized children in waves. Conclusion. During early life nasopharyngeal colonization by H. influenzae is a dynamic phenomenon with sequential carriage of various clones spreadin g in the community.