Long-term persistence of Schistosoma mansoni hotspots in western Kenya despite ongoing mass drug administration

Previous studies have reported the existence of ‘hotspots’, where schistosomiasis prevalence and infection intensity remain high despite regular preventive chemotherapy. Western Kenya is one region where such hotspots were reported. We investigated whether hotspots remain following eight years of school-based deworming programme by comparing the prevalence and infection intensity of Schistosoma mansoni between five randomly selected hotspots and non-hotspots in Siaya County, western Kenya. We conducted a cross-sectional study involving 500 participants (250 from hotspots and 250 from non-hotspots) between May and September 2023. The overall prevalence of Schistosoma mansoni in the ten villages was 39.4%. However, the average prevalence in the hotspots was 2.08 times higher than in the non-hotspots (adjusted prevalence ratio, Adj PR = 2.08, 95% CI: 1.65–2.66, P < 0.001). The intensity of infection was also significantly greater in hotspots than in non-hotspots ( P < 0.001). Males had infection prevalence 1.22 times higher than females ( Adj PR = 1.22, 95% CI: 1.0–1.5, P = 0.055), but gender had no impact on prevalence and intensity. Age impacted both prevalence and intensity as they were all significantly higher in individuals ≤ 18 years of age compared to those ˃ 18 years. These results demonstrate the long-term persistence of S. mansoni hotspots over 8 years, despite ongoing mass drug administration efforts targeting school children. These results underscore the necessity to reconsider current control strategies, which could include vector control and other water, sanitation, and hygiene (WASH)-based control measures in these persistent hotspots. • Schistosomiasis hotspots are a major impediment to the control of this disease. • Surveys conducted eight years apart revealed remarkable stability of schistosomiasis hotspots in western Kenya. • Infection prevalence and intensity were significantly greater in the selected hotspots compared to non-hotspots. • Annual mass drug treatment with praziquantel alone is insufficient to reduce transmission in hotspots.