Day-to-day variation of Schistosoma haematobium infection and intensity estimates in the near-elimination setting Pemba, Tanzania

Several areas are approaching the schistosomiasis elimination goals put forth in the World Health Organization roadmap for 2030. Yet, the low prevalence and infection intensities characteristic for near-elimination settings challenge accurate diagnosis and intervention decisions. We assessed the day-to-day variation of Schistosoma haematobium infections and intensity, proxied by urine microscopy among children in a near-elimination setting and discuss implications for elimination. This observational study was conducted in early 2025 in two schools in Pemba, Tanzania. Children provided 5 urine samples on different days that were subjected to urine filtration microscopy. Daily and cumulative proportions of infection and intensity were calculated. The observed day-to-day transitions in infection intensity were analysed. Complete data records were available for 270 children. The daily proportion of S. haematobium infection ranged from 18.9% (51/270) to 23.3% (63/270). The cumulative proportion increased from 21.2% (57/270) after examining a single urine sample to 35.6% (96/270) after examining 5 urine samples per child, resulting in a missed rate of 40.6% (39/96) when only one instead of 5 samples were examined. The increase was most pronounced for light intensity infections (from 13.3% (36/270) to 25.9% (70/270)). Very few infected children (6.3%, 6/96) stayed in the same infection intensity category across all 5 days. Among them, 5.2% (5/96) consistently had a heavy and 1.0% (1/96) a light infection. Schistosomiasis control and elimination programmes relying on single-sample urine filtration microscopy likely miss a substantial proportion of light intensity infections, leading to an underestimation of the true prevalence, which can impede intervention decisions and jeopardise elimination targets. Multiple urine samples should be examined for an accurate diagnosis that will guide treatment and intervention assignment in near-elimination settings. Trial registrationhttps://clinicaltrials.gov/study/NCT06808750.