Objective: To obtain insight into the present incidence of pertussis.
Design: Observational study of data from different sources of surveillance.
Method: For the years 1989-1994 the incidence of pertussis was estimated from the number of pertussis notifications, from laboratory data or serodiagnosis, from isolations of Bordetella and from the national registration of clinical diagnosis of hospital admissions.
Results: The numbers of notifications and positive serology yielded similar average yearly incidences for the period 1989-1994 (2.4 and 2.3/100.000 respectively). According to notifications and positive serodiagnosis, respectively, peak incidences occurred in 1989 (3.5 and 2.4/100.000) and 1994 (4.2 and 4.1/100.000). In 1993 the incidence of positive serodiagnosis (3.2 per 100.000) was also higher than in the other years. The incidence based on hospitalizations, notifications and positive serology was highest among children under 1 year of age. In the period 1989-1993 no deaths were recorded. The vaccine efficacy amounted to 91%.
Conclusion: For 1989-1994 the pattern over time was mostly consistent with pertussis being an endemic disease in childhood with 4-yearly peaks. The incidence of hospitalizations emphasized the seriousness of the illness in infants. It is important that general practitioners are on the alert for the occurrence of pertussis in vaccinated and unvaccinated children and adults.