Abstract
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.
Highlights
Soil-transmitted helminth infections inflict a significant burden on the world’s poorest populations living in rural or deprived urban settings in developing countries [1,2]
We studied the effect of stool sampling efforts and the use of different diagnostic techniques on the measured prevalence of worms, including hookworm, large intestinal roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and dwarf threadworm (Strongyloides stercoralis) in Zanzibar, where worm control has been implemented over the past decade
The observed prevalence of the different worms increased with an enhanced sampling effort and when different diagnostic methods were combined
Summary
Soil-transmitted helminth infections inflict a significant burden on the world’s poorest populations living in rural or deprived urban settings in developing countries [1,2]. Pre-school as well as school-aged children and pregnant women are the groups at highest risk of morbidity due to these infections [5,6] Strongyloides stercoralis is another important human helminth species, with disseminated infections being potentially fatal [7,8]. Single-dose anthelminthic treatment, usually without prior diagnosis administered to high-risk groups, is the strategy of choice. This approach has been termed ‘preventive chemotherapy’ [10]. A decreased number of worms results in a decline of egg excretion and, in reduced environmental contamination and transmission For both reasons the success of mass drug administration is more accurately measured if infection. We focused on schoolchildren on Unguja Island, Zanzibar, an area where anthelminthic drugs have been repeatedly administered over the past decade
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