Estimating incidence of whooping cough over time: a cross-sectional recall study of four Swedish birth cohorts.

Incidence of whooping cough was studied in Göteborg, Sweden, in four random samples of birth cohorts from 1972, 1977, 1978 and 1980. To obtain data a postal questionnaire to parents was used and methodologically explored. Vaccination data were taken from health cards. Four years after stopping vaccination cumulative incidence in the unvaccinated cohort born 1980 had risen to levels of the prevaccination era. Sex differences in susceptibility were not seen. Efficacy of the Swedish manufactured non-adsorbed whole cell pertussis vaccine was low. In a developed country like Sweden a cross-sectional study of random samples from the community with recall data may give useful information on the incidence of a disease like whooping cough at a comparatively low cost.