Serologic studies in 11,460 pregnant women during the 1972 rubella epidemic in Israel.

A total of 11,460 women in the first 4 months of pregnancy, either exposed to or with suspected clinical rubella were tested for rubella antibody during an extensive epidemic of this disease in 1972. The proportion of women who were seronegative decreased from 25% at the beginning of the epidemic to 16% toward the end. In 542 (79%) of 682 cases with suspected clinical rubella, the laboratory findings were consistent with recent rubella infection, while in the remaining 140 cases of suspected clinical rubella recent infection could be excluded by serologic tests. CF tests were more useful than HI for confirmation of clinical rubella, and especially for retrospective diagnosis, since elevated titers (larger than or equal to 1:16) were suggestive of recent infection. Paired sera were tested from 4203 patients exposed to rubella: 1126 of the subjects were seronegative and the remaining 3077 seropositive (HI larger than or equal to 1:16) on first testing. In the seronegative group, 278 seroconversions were detected (24.6%): 247 cases of clinical rubella (21.9%) and 31 seroconversions without clinical symptoms (2.7%). Among the seropositive subjects in 2306 instances (74.9%) recent subclinical rubella could be excluded by low and stable HI or CF antibody titers in paired sera. In 32 (1.1%) an antibody rise (HI or CF) without clinical symptoms was detected, and in the remaining 739 (24%) high CF titers were found in paired sera, and these were classified as suspected subclinical rubella.