The epidemiology of rubella virus infections in a large city of southern Italy.

Serum titers of anti-rubella antibodies were measured in 4,424 babies and children (aged 0-15 years) and in 2,362 females of childbearing age by a microhemagglutination-inhibition technique. Sera were screened for IgM antibodies with an enzyme-linked immunosorbent assay; positive sera were titrated in a capture immunoenzymatic test. The incidence of serological positive response, high at birth and in the first 6 months of life (65.0%), declined in the older age-groups (60.2% from 6 to 12 months, 57.0% from 1 to 2 years, 54.2% from 2 to 3 years, 55.2% from 3 to 6 years). Over 6 years, the incidence increased progressively (63.9% from 6 to 9 years and 76.1% from 9 to 15 years). In females aged 15-45 years the seronegativity rate was 8.6%. Circulation and transmission of the virus can only be blocked by the attainment and maintenance of high immunization levels. The high incidence of seronegativity among females of childbearing age stresses the importance of pre-marital determination of serological reactivity towards the rubella virus and underlines the importance of vaccination in seronegative women.