RUBELLA IN TRINIDAD: SERO-EPIDEMIOLOGIC STUDIES OF AN INSTITUTIONAL OUTBREAK

An epidemic of rubella occurred in a home for the mentally retarded in Trinidad during 1967. Forty per cent of resident patients and staff members developed rubella with rash, as did 15% of non-resident students and staff. Sero-epidemiologic studies were carried out among 66 residents of the female in-patient wing. Only 8 (12%) appeared to have been immune prior to the outbreak. Twenty-three (35%) developed rubella with rash, while 34 (51%) had non-rash infection, as demonstrated by a 4-fold or greater rise in serum rubella hemagglutination-inhibition antibody titer. The overall ratio of rash to non-rash illness was 1:1.5. However, the proportion of infections with rash was higher for children within the first decade of life. Only 1 of 58 susceptibles escaped infection during the epidemic. These results indicate that, in a closed, largely susceptible population, rubella is a highly infectious disease. The true extent of spread is masked by the high proportion of infections unaccompanied by rash.