Serological survey on the immunity to diphtheria of the northern Greek population.

The recent outbreak of diphtheria in the Newly Independent States (NIS) of the former USSR and the immigration from these high risk areas to Greece prompted us to determine the diphtheria antitoxin levels by enzyme-linked immunosorbent assays (ELISA) in 509 healthy individuals (307 males and 202 females) from northern Greece. The population under study was divided in ten age groups from 1 day to > 60 years old. Diphtheria antitoxin levels of > or = 0.1 IU/ml were considered as protective ones. 44.6% of the examined people were found susceptible. The children up to their twenties seem to be immune to diphtheria in a high proportion (86-88.4%). The diphtheria antitoxin levels declined sharply above this age (17.6% in the age group 21-30 years old). The level of protection in adults appeared to be higher in the oldest group (49%). According to these results, the adults are not properly protected. Booster doses of vaccine for them are recommended to improve the resistance of the northern Greek population from possible infection by toxigenic stains of Corynebacterium diphtheriae, imported or endogenous.