Low prevalence of diphtheria immunity in the Spanish population: results of a cross-sectional study

Abstract

A seroepidemiological study was conducted on a representative sample ( n=3944) of the Spanish population to assess the immune status to diphtheria. A total of 1907 men and 2037 women in the 5–59 years age range were stratified by sex and age (5–12, 13–19, 20–29, 30–39, 40–49, 50–59 years). Concentrations of toxin antibodies were measured using a commercial ELISA kit. Samples with titres≥0.1 IU/ml were considered to show full protection. Only 26% (95% CI: 25–28%) of the overall population studied was fully protected. The highest number of subjects with uncertain or no protection was found in the 20–39 age group (>85%). The prevalence of fully protected subjects progressively declined from 51% for the 5–12 year age group, to 14% for the 30–39 year age group, whereas it increased to 20% and 35% for the 40–49 and the 50–59 year age groups, respectively ( p<0.0001). These results stress the need to intensify vaccination programs in adolescents and adults with periodic booster doses of diphtheria toxoid.