A bacteriological and helminthological investigation of a sewage-irrigated area in a Beijing suburb

The municipal sewage and raw sludge removed from a sewage treatment plant were the main sources of pollution by pathogenic bacteria and helminthic eggs in land utilization. The level of pollution in the sewage-irrigated areas was as high as that in the areas using fresh night soil. The survival time of Salmonella and Ascaris ova in soil irrigated with sewage was relatively long. The soil had a definite natural capacity for purifying pathogenic bacteria. Because of the different ways of watering, the number of Salmonella detected on vegetables irrigated with sewage was higher than that on vegetables manured with night soil, whereas the reverse held for the number of Ascaris ova. The differences in latent Salmonella infection and the geometric mean titer of serum agglutination for typhoid between the vegetable growers living in the sewage-irrigated area and those living in fresh night soil areas were not remarkable. The prevalence of soil-transmitted ascaridiasis among vegetable growers in sewage-irrigated areas was slightly lower than that among growers in fecal-contaminated areas. When the number of fecal coliforms in sewage was no greater than 10(4)/liter and no less than 85% of Ascaris ova could be removed by sewage treatment, the number of Salmonella and Ascaris ova detected decreased noticeably.