Abstract
The changes in the intensity of Schistosoma haematobium infection, incidence and conversion/reversion ratio in a community were observed over a period of 1.5 years. The intensity of infection was judged by two indices : egg counts per 10 ml of urine and egg counts per hour. During the study period, 4 urine examinations were conducted at 6-month intervals. Subjects were included in the analysis of the changes in the intensity of infection in a community if they took all 4 urine examinations and were positive for eggs. The changes in the intensity of S. haematobium infection differed considerably according to the indices used. The changes in the intensity of infection were compared with the changes in the level of transmission expressed by incidence and conversion/reversion ratio or with the changes in the urine volume. The changes in the intensity of infection expressed by egg counts per hour closely paralleled the changes in both incidence and conversion/reversion ratio in a community, regardless of urine volume. By contrast, when the intensity of infection was expressed by egg counts per 10 ml of urine, it did not correlate with the changes in the level of transmission, and was negatively related to the changes in urine volume. These results suggest that egg counts per hour is a reliable index that accurately reflects the changes in the intensity of S. haematobium infection in a community.
