Measuring exposure to S. japonicum in China. II. Activity diaries, pathways to infection and immunological correlates

In this study we examine the pathways to schistosomiasis exposure and infection among residents residing on two islands (large, Qingshan; small, Niangashan) in the Dongting Lake region (Hunan province) of China. An exposure model, based on activity diaries, was used to quantify an individual's square-metre-minute (sq.m.min) daily water contact. Subjects living on the small island had a significantly higher (P=0.0002) degree of exposure (mean±S.D., 13.2±11.0 sq.m.min) than individuals dwelling on the large island (mean±S.D., 5.5±7.1 sq.m.min). Participants identified as stool egg positive (mean±S.D., 8.3±10.4 sq.m.min) had higher exposures than for those never treated (mean±S.D., 2.2±3.4 sq.m.min) for schistosomiasis, and these high exposures rose steadily to peak at 35-49 years of age and decline after age 50. This exposure pattern differs markedly from those reported for African or South American schistosomiasis. The majority of human water contact occurs on the lake. Egg-positive subjects reported significantly higher (