Focal Prevalence Survey of Schistosomiasis in South Cotabato, Philippines

Abstract Background: Schistosomiasis has long been endemic in South Cotabato. Fourteen barangays in Koronadal City and Tantangan, covering over 82,000 people at risk, had received more than a decade of mass drug administration with praziquantel when a focal prevalence survey was conducted in 2016. The survey aimed to update local prevalence estimates, document other helminth infections, and assess the Kato–Katz technique. National data since then have shown declining prevalence in many endemic areas, although persistent animal reservoirs continue to be reported. As the Department of Health pursues transmission interruption by 2025, reporting the 2016 findings remains important for assessing progress and guiding elimination strategies. Methods: Individuals aged 5-65 years from households selected through stratified cluster sampling were invited to submit stool specimens. Local medical technologists were recruited and trained to conduct parasitologic assessment using Kato-katz technique. Each specimen from the 4,387 samples (2,344 from Koronadal and 2,043 from Tantangan) was tested for the presence of Schistosoma japonicum , soil-transmitted helminths, and other intestinal parasite ova. The sensitivity of the field testing was determined through validation of the slides by reference microscopists of the College of Public Health/National Institutes of Health, University of the Philippines Manila. Results: No schistosomiasis cases were detected in Koronadal City. In Tantangan, nine cases were identified in four barangays, corresponding to a prevalence of 3.6 per 1,000 population (95% CI: 1.7–7.8 per 1,000). After adjustment for sampling weights and non-response, the combined prevalence for both municipalities was 0.098%. One barangay, New Lambunao (1.87%), exceeded the <1% near-elimination threshold. Eight infections were of light intensity and one was moderate; no heavy-intensity infections were detected. Soil-transmitted helminths were also identified, with Ascaris lumbricoides (7.29%) being most prevalent. Validation showed high specificity (>98%) and sensitivity of 88.9% for schistosomiasis. Conclusion: The 2016 focal survey demonstrated very low schistosomiasis prevalence in South Cotabato following long-term MDT, with most endemic barangays meeting the <1% near-elimination threshold. However, given the limitations of Kato–Katz in low-intensity settings and the potential influence of post-treatment timing on egg detection, updated focal surveys incorporating more sensitive diagnostic tools are recommended. Strengthened surveillance, integrated helminth control, and a One Health approach will be essential to verify transmission status and guide decisions on sustaining or modifying MDA as the country works toward its 2025 elimination goal.