IMMUNITY TO DIPHTHERIA IN SIENA

The aim of this study, carried out in 1993, was to evaluate diphtheria immunity in Siena. Diphtheria antitoxin levels were measured by means of the immunoenzymatic test (ELISA) in serum samples of 602 apparentl y healthy subjects (239 males and 363 females) of all ages residing in Siena. According to widely used criteria, 6% of the total population were susceptible to diphtheria (antibody levels < 0.01 IU/ml), 71% had basic protection (0.01-0.09 IU/ml) and 23% were fully protected (grea ter than or equal to 0.1 IU/ml). The results suggested that a high pro portion of young population had a protective level of immunity against diphtheria, that susceptibility increased with age and a smaller prop ortion of males (2.9%) than females (8.3%) were unprotected; this diff erence was statistically significant. Our results suggest that it may be useful to revaccinate adults with low levels of diphtheria toroid s o that the percentage that remains unprotected does not put the commun ity at risk of an outbreak of diphtheria.