Identifying hotspots of S. haematobium infection following praziquantel treatment during multiple annual mass drug administration campaigns in Zimbabwe

Urogenital schistosomiasis is contracted from the Schistosoma haematobium parasite and is treated with the drug praziquantel (PZQ). Despite MDA interventions, persistent hotspots (PHS) of S. haematobium infection have been identified in multiple schistosome endemic African countries but have yet to be characterised in Zimbabwe. This study assessed long-term infection persistence and variability in praziquantel (PZQ) efficacy among school-aged children (6-15 years) in 29 districts of Zimbabwe, using data from MDAs conducted between 2012 and 2017. Metrics included infection prevalence, mean egg count, and treatment efficacy indicators. Two hotspot definitions were applied: (i) prevalence-based persistent hotspots (PPHS), identified by limited reduction or rebound in prevalence; and (ii) efficacy-based persistent hotspots (EPHS), defined by cure rates below 70%. Statistical comparisons between hotspot and non-hotspot ("responder") districts used regression models, Fisher's exact test and Mann-Whitney U tests. Analyses revealed four PPHS and six EPHS. PPHS districts exhibited significantly higher baseline prevalence and infection intensity compared with responders (P = 0.043), a pattern not observed for EPHS. Greater distance from freshwater sources was associated with EPHS occurrence (P = 0.016), although this appeared to be an indirect effect of initially high infection intensities. Lower treatment frequency correlated with increased hotspot occurrence, but the relationship was not statistically significant for either hotspot category. Other investigated factors including treatment coverage, timing of drug administration and ecological suitability for intermediate host snails showed no significant association with hotspot status. The elevated initial prevalence and infection intensity in PPHS suggest these indicators could be used for early hotspot identification, enabling targeted adjustments in intervention strategies. The findings underscore the limitations of relying solely on preventive chemotherapy in high-transmission settings. Integrating complementary measures such as water, sanitation and hygiene (WASH) interventions and snail control may improve outcomes, particularly in hotspot areas. In conclusion, the persistence of S. haematobium hotspots in Zimbabwe highlights the need for adaptive, integrated control approaches aligned with the WHO's 2030 roadmap. Monitoring baseline epidemiological indicators could facilitate earlier detection of persistent transmission foci, guiding more effective and sustainable schistosomiasis control.