Rubella outbreak on Tokunoshima Island in 2004: A population-based study of pregnant women

Aim:  The purpose of this study was to clarify the risk of rubella infection for pregnant women in the outbreak area. Material & Methods:  We performed a retrospective, population-based study on all 232 pregnant women during the rubella outbreak period in Tokunoshima Island. All women had a rubella hemagglutination inhibition (HI) titer drawn during their current pregnancy. In 61 women, HI titers were compared between the current and past pregnancies. Rubella IgG antibody titers were measured and IgG avidity index (AI) was calculated for 92 non-infected pregnant women. Results:  Of the 232 candidates, 22 pregnant women contracted rubella infection (congenitally infected infants: 2). Seventeen of 61 pregnant women showed a four-fold or greater elevation in HI titer when compared with previous titers. Their previous HI titers were all ≤64. Low IgG AIs (<30%) were only observed in women with a HI titer of ≤64 (92 non-infected women). Conclusions:  The risk of maternal rubella infection in the outbreak was as follows: non-immunized pregnant woman and pregnant woman with a rubella HI antibody titer ≤64 and low IgG AI.