BackgroundSoil-transmitted helminth infections are common throughout the tropics and subtropics and they disproportionately affect the poorest of the poor. In view of a growing global commitment to control soil-transmitted helminthiasis, there is a need to elucidate the effect of repeated stool sampling and the use of different diagnostic methods in areas targeted for preventive chemotherapy that are characterized by low-infection intensities. In this study, we focused on schoolchildren on Unguja Island, Zanzibar, an area where anthelminthic drugs have been repeatedly administered over the past decade.Methodology/Principal FindingsThree serial stool samples from each of 342 schoolchildren were examined using the Kato-Katz (K-K), Koga agar plate (KAP), and Baermann (BM) techniques. These methods were used individually or in combination for the diagnosis of Ascaris lumbricoides (K-K), Trichuris trichiura (K-K), hookworm (K-K and KAP), and Strongyloides stercoralis (KAP and BM). The examination of multiple stool samples instead of a single one resulted in an increase of the observed prevalence; e.g., an increase of 161% for hookworm using the K-K method. The diagnostic sensitivity of single stool sampling ranged between 20.7% for BM to detect S. stercoralis and 84.2% for K-K to diagnose A. lumbricoides. Highest sensitivities were observed when different diagnostic approaches were combined. The observed prevalences for T. trichiura, hookworm, A. lumbricoides, and S. stercoralis were 47.9%, 22.5%, 16.5%, and 10.8% after examining 3 stool samples. These values are close to the ‘true’ prevalences predicted by a mathematical model.Conclusion/SignificanceRigorous epidemiologic surveillance of soil-transmitted helminthiasis in the era of preventive chemotherapy is facilitated by multiple stool sampling bolstered by different diagnostic techniques.

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'Kick-out-Kichocho' is an integrated helminth-control initiative that is aimed at reducing the burden of urinary schistosomiasis and soil-transmitted helminthiases (STH) on Zanzibar Island (Unguja), in Tanzania. Like other initiatives based on preventive chemotherapy, the programme is mainly school-based and, consequently, pre-school children (aged < or =6 years) are not targeted specifically. To assess the importance of urinary schistosomiasis, STH and malaria, as well as the occurrence of anaemia and growth retardation among these younger children, an epidemiological survey has been undertaken, in a rural area of Unguja, among 152 pre-school children and their 113 mothers. In the pre-school children investigated, urinary schistosomiasis was rare because of the children's lack of contact with environmental water. Malaria was also rare in the children, probably as a consequence of the study season, the widespread use of insecticide-treated bednets and the good access to first-line antimalarial drugs. In contrast, the prevalences of infection with at least one soil-transmitted helminth and of anaemia were alarmingly high among the pre-school children, at 50.0% [95% confidence interval (CI)=40.4%-59.6%) and 73.4% (CI=?65.2%-80.5%), respectively; the corresponding values in the children's mothers were 35.2% (CI=25.4%-45.9%) and 25.9% (CI=18.0%-35.3%). In the rural study area, Kandwi was identified as a hamlet with particularly high levels of transmission of soil-transmitted helminths, and household aggregations of STH were common. To reduce the present health inequities, the future integration of pre-school children within ongoing anthelmintic-control programmes in schools is strongly recommended.