The incidence of Bordetella pertussis infections estimated in the population from a combination of serological surveys

Objectives: Bordetella pertussis circulates even in highly vaccinated populations. There is a considerable amount of infection in adults. For designing more effective vaccination schedules it is important to quantify the age-dependent relation between the number of notified cases and the number of infections. Methods: We used a statistical relationship between the time since infection and the IgG antibody titers against pertussis toxin, derived from a longitudinal data set, to estimate time since infection for all individuals in a cross-sectional poputation-based study (1995-1996) based on their titers. Age-specific incidence of infection with B. pertussis was calculated and compared with the age-distribution of notified cases of pertussis in 1994-1996. Results: Estimated incidence of infection was 6.6% per year for 3-79-year olds, annual incidence of notified cases 0.01%. Estimated age-specific incidence of infection was lowest for 3-4-year olds (3.3%) and increased gradually up to the age of 20-24 years (10.8%). The number of notified cases was highest for 3-9-year olds. Conclusions: In the Dutch population B. pertussis infections occur more frequently and in elder age-categories then suggested by notifications. Mathematical modeling could explore what booster vaccination strategies are most effective in reducing severe disease among not (completely) vaccinated infants. (C) 2005 The British Infection Society. Published by Elsevier Ltd. All rights reserved.