[Pediatric surveillance of invasive infections caused by Haemophilus influenzae type b in children in the period following introduction of vaccination]

Abstract

Objective: Evaluation of the effect of vaccination against Haemophilus influenzae type b (Hib) on the occurrence of invasive Hib infections in children since its introduction into the national immunization programme in April 1993.

Design: Observational study.

Setting: Nationwide investigation.

Method: Data collected through active surveillance of invasive Hib infections by paediatricians for the period from October 1993 to September 1994 (11 months) were compared with data from the meningitis surveillance by the Netherlands Reference Laboratory for Bacterial Meningitis.

Results: A total of 139 paediatric reports of invasive disease by H. influenzae concerned 57 cases of only meningitis, 35 of meningitis with sepsis, 2 of meningitis with arthritis, one of meningitis with arthritis and osteomyelitis, 34 of epiglottitis including one case with sepsis, 8 of only sepsis and 2 of only arthritis. All proven infections by Hib occurred in children who had not or incompletely been vaccinated. One child with sepsis had had three vaccinations and became ill five months later; the isolated bacterial strain was not serotyped. Typing was performed in only 80% of the isolates, of which 98% were of type b. Appropriate culturing and typing was often omitted in case of epiglottitis.

Conclusion: The effect of vaccination against Hib became apparent in a small number of cases of invasive Hib disease reported by paediatricians; the peak incidence of meningitis no longer occurred in children under one year of age but in children aged one year. The paediatric surveillance described offers possibilities for monitoring Hib epidemiology.