The re-emergence of pertussis in Israel.

BACKGROUND Pertussis is the only vaccine-preventable disease that has re-emerged in Israel. The reported crude incidence of the disease increased 16-fold since 1998. OBJECTIVES To describe the epidemiology of pertussis and explain the substantial increase in reported pertussis incidence in Israel in recent years. METHODS Crude and specific pertussis incidence by age, patient immunization status, hospitalization rate, and national immunization coverage rate were calculated from information provided by the public health offices of the Ministry of Health. RESULTS The reported crude incidence of pertussis increased from 1-2/100,000 in 1994-98 to 23/100,000 in 2004. The trend was observed in all age groups, being most prominent in infants under age 1 year and in children aged 5-14. The incidence of pertussis was substantially higher in unvaccinated and partly vaccinated compared to fully vaccinated persons. Fifteen percent of notified cases were hospitalized, but in infants under age 1 year the hospitalization rate was 50%. National pertussis immunization coverage by age 2 years was stable during the last 10 years. CONCLUSIONS There are several possible explanations for the re-emergence of pertussis in Israel. The most plausible reason seems to be the waning of vaccine-induced immunity in face of infrequent natural exposure to the infectious agent and lack of a pertussis vaccine booster dose after age 1.