Case-control study on encephalopathy associated with diphtheria-tetanus immunization in Campania, Italy.

Between 1980 and 1982 in the Campania region of Italy, several cases of encephalopathy in children who had only a week previously been given diphtheria-tetanus immunizations were reported to the Italian Ministry of Health in Rome. A case-control study was therefore set up to test the association between the syndrome and immunization. For this purpose, cases were defined as children between 3 and 48 months who had been admitted to an intensive care unit with symptoms such as convulsions of unknown origin, Reye's syndrome, or death from unknown causes. The fatality rate from encephalopathy among the immunized children in the study was 25 out of 29 (86%). In Campania (population 5.4 million), the annual incidence of encephalopathy associated with diphtheria-tetanus immunization was estimated to be 2.9 per 100 000 doses of the vaccine.