The sero-epidemiology of diphtheria in Western Europe

Seven countries in Western Europe collected large, representative serum ban ks across the entire age range and tested them for diphtheria anti-toxin (s ample size ranged from 2991 to 7715). Although a variety of assays were use d, the results were all standardized to those of a reference laboratory and expressed in international units. The standardization process, and the ava ilability of similar, large data sets allowed comparative analyses to be pe rformed in which a high degree of confidence could be ascribed to observed epidemiological differences. The results showed that there were large diffe rences in the proportion of adults with insufficient levels of protection a mongst different countries. For instance, roughly 35% of 50- to 60-year-old s were found to be seronegative (titre less than or equal to 0.01 IU/ml) in Finland compared with 70-75 % in the United Kingdom. Furthermore, the prop ortion of seronegative adults would be expected to increase in some countri es, notably Italy and the western part of Germany. In those countries with vaccination of military recruits there was a marked sex-related difference in the proportion of seropositive individuals. All countries have high leve ls of infant vaccine coverage (> 90 %) but the accelerated schedule in the United Kingdom appears to result in lower anti-toxin titres than elsewhere. In Sweden, booster doses are not offered until 10 years of age which resul ts in large numbers of children with inadequate levels of protection. Altho ugh the United Kingdom and Sweden both have higher proportions of seronegat ive children than elsewhere the likelihood of a resurgence of diphtheria in these countries seems remote.