Epidemiology of pertussis in French hospitals in 1993 and 1994: thirty years after a routine use of vaccination

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Abstract
Despite widespread vaccination during 30 years, the hypothesis of a resurgence of pertussis in France has been raised by outbreaks and sporadic case reports. No surveillance data were available after 1985. A survey was undertaken in 1993 and 1994 in a pediatric hospital network able to confirm cases; the network (22 hospitals) represents 19.6% of pediatric admissions in France. Case definition included clinical (≥21 days of paroxysmal cough), laboratory-confirmed (culture or serology by immunoblot) or epidemiologically confirmed pertussis (documented contact with a laboratory-confirmed case). The pattern of transmission was studied in the household. Vaccine status was obtained from health records. during a 15-month period 560 cases (316 index cases, 244 household contact cases) were reported; 49% of index cases and 20% of contact cases were confirmed by culture and/or serology. Sixty-five percent of index cases were 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 duration of 2 weeks. Infection was acquired from parents (34%) and siblings (46%). Seventy-three percent of index cases were unvaccinated. Although pertussis vaccination coverage is very high in France, the organism is still circulating, affecting, within the pediatric population, mostly non- or incompletely vaccinated infants. These results strongly support the importance of adhering to the immunization schedule and suggest introducing booster dose(s) to prolong vaccine immunity and reduce the exposure to Bordetella pertussis of infants too young to be immunized.