EPIDEMIOLOGY OF PERTUSSIS IN FRENCH HOSPITALS IN 1993 AND 1994 - 30 YEARS AFTER A ROUTINE USE OF VACCINATION

Background. Despite widespread vaccination during 30 years, the hypoth esis of a resurgence of pertussis in France has been raised by outbrea ks and sporadic case reports. No surveillance data were available afte r 1985. Methods. A survey was undertaken in 1993 and 1994 in a pediatr ic hospital network able to confirm cases; the network (22 hospitals) represents 19.6% of pediatric admissions in France. Case definition in cluded clinical (greater than or equal to 21 days of paroxysmal cough) , laboratory-confirmed (culture or serology by immunoblot) or epidemio logically confirmed pertussis (documented contact with a laboratory-co nfirmed case). The pattern of transmission was studied in the househol d, Vaccine status was obtained from health records. Results. during a 15-month period 560 cases (316 index cases, 244 household contact case s) were reported; 49% of index cases and 20% of contact cases were con firmed by culture and/or serology. Sixty-five percent of index cases w ere younger than 1 year of age (the incidence in this age group could be estimated to be 95/100 000) and 66% were hospitalized for a mean du ration of 2 weeks. Infection was acquired from parents (34%) and sibli ngs (46%). Seventy-three percent of index cases were unvaccinated. Con clusions. Although pertussis vaccination coverage is very high in Fran ce, the organism is still circulating, affecting, within the pediatric population, mostly non- or incompletely vaccinated infants. These res ults strongly support the importance of adhering to the immunization s chedule and suggest introducing booster dose(s) to prolong vaccine imm unity and reduce the exposure to Bordetella pertussis of infants too y oung to be immunized.