Diphtheria antibody levels in the Italian population

Immunity to diphtheria was assessed in serum samples obtained from 3111 hea lthy Italian males and females aged 0-84 years. Diphtheria antitoxin was te sted using a double-antigen, time-resolved fluorescence immunoassay (DA-DEL FIA). According to internationally accepted criteria, antitoxin concentrati ons <0.01 IU/ml indicate susceptibility to diphtheria, those greater than o r equal to 0.01-0.09 IU/ml provide basic or inadequate protection, and conc entrations greater than or equal to 0.1 IU/ml are protective. By these crit eria, 9.9% (95% CI, 8.9 to 11.18) of the participants were susceptible to d iphtheria, 30.2% (95% CI, 28.6 to 31.9) had basic protection, and 59.9% (95 % CI, 58.1 to 61.6) were protected. The prevalence of unprotected individua ls showed an age-related increase, up to the 45-49-year-old age group for f emales and the 50-54-year-old age group for males (34.9% and 31.3% of indiv iduals, respectively). The prevalence of immunity did not significantly dif fer in relation to sex in any of the age groups. These results indicate tha t booster shots should be routinely provided to the adult population in ord er to maintain a protective level of diphtheria antibodies.