Comparative seroepidemiology of diphtheria in six European countries and Israel

Received 9 March 2011; Final revision 31 January 2012; Accepted 31 January 2012;first published online 24 February 2012SUMMARYSerological surveys for diphtheria were conducted in six European countries including CzechRepublic, Hungary, Ireland, Latvia, Luxembourg, Slovakia and one country outside Europe,Israel. For each country, a nationally representative population sample was collected across theentire age range and was tested for antibodies to diphtheria toxin. Although each nationallaboratory used its preferred assay, the results were all standardized to those of the in vitroneutralization test and expressed in international units (IU) which allowed comparative analysesto be performed. The results showed that increasing age is related to a gradual increase inseronegative subjects (<0.01 IU/ml of diphtheria antitoxin antibodies). This may reflect waningimmunity following childhood vaccination without repeated booster vaccinations in adults.Differences in seronegativity were also found according to gender. In subjects aged 1–19 years,geometric mean titres of antitoxin are clearly related to the different vaccination schedules used inthe participating countries. Although clinical disease remains rare, the susceptibility to diphtheriaobserved in these serosurveys highlights the importance of strengthened surveillance.Key words: Diphtheria, immunoepidemiology, serology.INTRODUCTIONBefore the introduction of mass and routine im-munization, diphtheria was a common cause of mor-bidity and mortality. The disease was characterizedby periodic epidemics, with the last major Europeanepidemic occurring during the 1940s. With socio-economic improvement and the introduction of massinfant immunization during the 1940s and 1950s,there was a marked reduction in the incidence of in-fection in Europe [1, 2]. The incidence reached an all-time low in 1980 when only 623 cases were reportedfrom the European region of the World Health