Short-term Prediction of the Incidence of Congenital Rubella Syndrome.

Objectives In Japan, a rubella outbreak occurred from early 2012 to late 2013, primarily among adult males aged 20-49 years. We conducted this study to predict the number of congenital rubella syndrome (CRS) cases in Japan in 2014. Methods The probability of CRS when a pregnant woman is infected with rubella depends on the gestational age of the fetus. The cumulative number of CRS cases was predicted by a formula based on the parameters from two studies conducted in the U.K. and the U.S., the reported cases of rubella among women 15-49 years of age, and the reports of CRS from 2011 to week 2 of 2014. Findings While the predicted number of cases of CRS based on parameters from the U.K. study demonstrated a biphasic curve, with a low peak around week 12 and a high peak around week 50 of 2013, the predicted number of CRS cases based on the U.S. study demonstrated a single peak around week 50 of 2013. The ex post evaluation indicated that the cumulative number of CRS cases in 2014 would be 19.1-29.3. Interpretation Our prediction of the number of CRS cases may be useful for the enhanced detection of this often under-reported syndrome.