Fig 1. Flow diagram of study enrollment.

Fig 1 shows the enrollment process of adult rubella (n = 82) and adult non-rubella (n = 139) cases. Rubella-specific IgM was used for the enzyme immune assay (EIA) kit. Strong positive was defined as ≥ 1.21 at first hospital visit. Paired positive was defined as the second strong positive, although the first rubella IgM test was either weak (0.8–1.2) or negative (< 0.8).