The impact of passive chemotherapy on Schistosoma mansoni prevalence and intensity of infection in the Egyptian Nile Delta

We investigated the impact of the passive surveillance and treatment program of the Egyptian Ministry of Public Health on the prevalence and intensity of Schistosoma mansoni infection in the northern Nile Delta region of Egypt. The study was based on a large probability sample of the entire rural population of Kafr El Sheikh. Infection and egg counts were determined by examination of stools using the Kato technique. From a sample of 18,777 villagers, 15,017 provided stool specimens. A detailed history of treatment for schistosomiasis was obtained by interview using standardized questions in colloquial Arabic. A positive history of therapy for schistosomiasis was common, with more than 40% of the participating villagers reporting prior treatment. Treatment was further characterized by frequency, dates, type, and where it had been received. In both male and female adults, a positive history of treatment with praziquantel was associated with a significantly reduced prevalence of S. mansoni infection. For example, odds ratios for 20- 24-year-old males and females who did not indicate prior treatment were 5.2 (95% confidence interval [CI] = 2.3-7.2) and 6.5 (95% CI = 3.7-9.1), respectively. Geometric mean egg counts (GMECs) were significantly lower by more than two fold (P < 0.01) in both male and female adults who indicated prior treatment. The largest differences in prevalence and GMEC between those with or without a history of prior treatment were seen in the young and middle-aged adults. These results support strengthening programs for encouraging villagers to seek examination and treatment, and strengthen the dissemination and availability of praziquantel in the rural endemic areas of the country.