[Surveillance and risk assessment system of schistosomiasis in Jiangsu Province. II. Surveillance pattern and effect of Oncomelania hupensis snail status in Dongtai City, Jiangsu Province].

Objective: To explore the method of Oncomelania hupensis snail surveillance in transmission-interrupted regions of schistosomiasis, so as to provide a new pattern for the surveillance of snail status in the transmission-interrupted areas.

Methods: In Dongtai County, north of Jiangsu Province where the transmission of schistosomiasis was interrupted, the surveillance of snail status was performed by means of the village-level general survey, village-level sampling survey, snail survey in key settings of township and county, and snail reporting by residents. In addition, quality-control snail sites were set up for quality control. The effectiveness and cost of the four methods of snail surveillance was compared.

Results: A total of 163 079 settings and 22 785.62 hm2 were surveyed in Dongtai County from 2008 to 2013, and 89 residual snail breeding sites were found, with a snail area of 1.48 hm2. The patterns of village-level general survey, village-level sampling survey, and snail survey in key settings of township and county were employed for investigation of 94 550, 45 033 and 23 496 settings, consisting of 57.98%, 27.61% and 14.41% of total settings, and 2, 0 and 6 settings were found with snails, with 0.021/thousand, 0, and 0.255/thousand detection rates of settings with snail breading sites, respectively. The pattern of snail survey in key settings of township and county was more effective than that of village-level survey to detect-snail breeding sites (χ2 = 19.158, P = 0). The recovery rate of quality-control snail breeding sites was 52.56%, 38.27% and 73.62% for the three patterns of snail survey, respectively, and the pattern of snail survey in key settings of township and county showed a higher quality for snail survey than that of village-level survey (χ2 = 111.597 and 85.991, both P = 0). During the period from 2008 to 2013, 289 person-times reported 279 suspected snail habitats and 1 501 living snails, and no Oncomelania snails were found. During the 6-year period, there were 1617.5, 964.7 and 527.7 thousand RMB invested for village-level general survey, village-level sampling survey, and snail survey in key settings of township and county, and the cost of snail survey per hm2 was 129.88, 133.6 and 162.57 RMB/hm2, respectively. The cost of village-level general survey and snail survey in key settings of township and county to detect a snail-breeding site was 808 800 and 88 000 RMB, respectively (t = 12.850, P = 0.000), and the cost of snail survey in key settings of township and county was 10.88% of that of village-level general survey.

Conclusion: The snail survey in key settings of township and county is a highly effective and high-quality method for snail surveillance, which miay serve as a prior way for the surveillance of snail status in the transmission-interrupted areas of schistosomiasis.