Combined testing for antibodies to rubella non-structural and envelope proteins sentinels infections in two outbreaks

Two separate outbreaks of Rubella occurred in Hamilton, Ontario, Canada, 7 yrs apart, with a peak incidence for both in the month of April. A total of 138 cases, 51 in 1978 and 87 in 1985, was observed, the majority being in adolescents and young adults 15-25 years of age. Cases were diagnosed by the presence of Rubella IgM antibody or the combination of a negative passive hemagglutination (Rubacell-Abbott) and a positive enzyme immunoassay (EIA) or hemagglutination inhibition (HI) test on a single serum or by seroconversion for Rubella IgG antibody. Routine screening of sera with the Rubacell test, which measures antibodies to nonstructural rubella proteins together with HI or EIA testing of the negatives, served as a sentinel for rubella infection in the community during both outbreaks. Rubacell antibodies usually appeared 2-3 wk after onset of infections, and when present contained either or both IgG and IgM. Only 8/103 cases had a history of Rubella vaccination. Two of three products of conception yielded rubella virus in cell culture.