Low prevalence of diphtheria antitoxin in children and adults in northern Germany

Recent outbreaks of diphtheria in neighbouring eastern European countries and in the Russian Federation prompted us to evaluate immunity to diphtheria in a sample of 400 healthy individuals (210 male, 190 female) from northern Germany. An age-stratified study population was chosen, including newborns, children, adults and elderly persons over 60 years divided into 8 subgroups of 50 persons each. Diphtheria antitoxin was tested by enzyme immunoassay. The median antitoxin titre was 0.39 IU/ml. There was no difference in the median antitoxin titres of men and women. Inadequate immunity to diphtheria was detected in more than 90% of the 400 individuals tested, including 4% who completely lacked immunity (titre < 0.01 IU/ml), a further 20% with minimal protection (titre 0.01-0.1 IU/ml) and the majority of 69% who showed relative protection for less than one year (titre 0.1-1.0 IU/ml). Only 7% exhibited lasting protection for more than five years (titre > 1.1). Newborns and persons over 50 years of age constituted the least protected groups, with significantly lower median antitoxoid titres than the other age groups (p < 0.001). The absence of protective immunity in 7 of the 50 newborns examined (14%) reflects the inadequate protection of women of reproductive age. Children aged 1 to 10 years were the best immunized and protected group. The results suggest that routine booster immunizations of the majority of the adult population would be advisable in view of the ongoing migration from and the visits to high-risk areas.