The half-life of Ascaris lumbricoides prevalence in Japanese school children.

In the present study, we examined the dynamic of school-health-based parasite control and the related socio-economic influences. This is an ecological study based on data from 46 prefectures in Japan. The exponential decay of Ascaris lumbricoides prevalence was calculated by iterative least-squares method. Pearson's correlation and multiple linear regression model analysis were performed to assess the associations between the prevalence of Ascaris lumbricoides in Japanese school children and socio-economic variables such as the prefecture income per capita, the percentage of primary industry, the population density per 1 km2, the diffusion rate of population under water supply, and the percentage of upper secondary school enrollment. The results indicated that the parasite carrier rate was higher in younger students. The half-life of Ascaris lumbricoides prevalence was approximately 3 years with significant variation among prefectures. Multiple regression analyses showed that the decrease of infection in elementary and lower secondary school children had a significant positive association with primary industry and a significant negative association with prefecture income per capita. The school-health-based parasite intervention differs by prefecture and has changed over time according to the respective prefectural stage of economic development.