Diphtheria Antitoxin Levels in the 14-30-Year Age Group in Italy

In order to verify diphtheria immunity a seroepidemiological survey was performed in 1996-1997. Serum samples were obtained from 501 subjects 14 years old, recruited at 8 schools in Rome, and from 490 subjects 20-30 years old recruited from 15 Italian regions. Serum diphtheria antitoxin was titrated using the Vero cell assay. The minimum protection level of antitoxin was set at$0.01\ {\rm IU}\ {\rm ml}^{-1}$. The results show that the younger population have a good immunity to diphtheria while a large proportion of young adults is devoid of protective levels of diphtheria antitoxin. Out of the 501 subjects 14 years old, 495 (98.8%) had a diphtheria antitoxin titre$\geq 0.01\ {\rm IU}\ {\rm ml}^{-1}$. Only 6 (1.2%) teenagers were susceptible. Out of the 490 subjects 20-30 years old, 109 (22.2%) were susceptible, 381 (77.8%) had a diphtheria antitoxin titre$\geq 0.01\ {\rm IU}\ {\rm ml}^{-1}$. The data stress for booster immunization at the end of junior high school.