In this study, we estimated the age-specific incidence of B. pertussis infection, based on a cross-sectional sero-epidemiological survey of the distribution of high anti-PT titer sera, established by standardized criteria [14]. Information about the sero-prevalence of high levels selleck products of anti-PT antibodies in combination with the post-infection antibody decline rate allows the quantification of the extent of B. pertussis infections in various age groups irrespective of clinical manifestation and

reporting compliance. The threshold titers employed in this study were of an equivalent level to those cut-offs reported by de Melker et al. as diagnostic of recent or active infection with B. pertussis [9]. High levels of anti-PT IgG antibody may also be due to previous vaccination. However, numerous results from clinical trials of acellular and whole-cell MK0683 solubility dmso vaccines

have shown that high antibody titers wane 12–18 months following the primary vaccination course in almost all vaccinees [15]. During the study period, primary pertussis vaccination in Israel has been targeted routinely only at the infant age group with a fourth shot administered at 12 months. No booster doses were given at the time of serum sampling to older age groups. Although anti-PT titers rapidly decrease to very low levels within 1 year following vaccination [16], the first 3 years of life were excluded from the analysis of incidence of infection in order to avoid an influence by previous exposure to vaccine. Our results clearly show that despite a high vaccination infant coverage rate (>93%) in Israel, there is still a considerable circulation of B. pertussis, particularly in adolescents and elderly. In 2000, about 2.4% (or 2448 per 100,000) of the Israeli population

older then 3 years of age had previously experienced infection next with B. pertussis revealing a striking discrepancy between rates of infection and rate of reported disease for several reasons. For example, pertussis is under-diagnosed and under-reported, as similarly observed in other countries; [12] and [17] in The Netherlands, the estimated rate of infection is more than 600-times higher than the notified case numbers [12]. Studies also suggest that only 40–50% of pertussis cases show a classic clinical manifestation of a paroxysmal cough [18], often leading to a misdiagnosis as a general respiratory infection and a failure to investigate for pertussis. Hence, the amount of under-reporting varies by age, and has been shown to be higher for older children, adolescents, and adults than for younger children. It is also well documented that individuals with a primed immune system develop a mild variant of the disease [19] and [20]. Based on our analysis, we are not able to determine the clinical manifestation of infections.