A national geostatistical survey for schistosomiasis and soil-transmitted helminths in Zimbabwe following interruption of preventive chemotherapy.

BACKGROUND

Schistosomiasis and soil-transmitted helminthiases (STH) are targeted for elimination as public health problems (EPHP) in Zimbabwe by 2030. A 2018 impact survey demonstrated prevalence below EPHP thresholds following seven rounds of annual preventive chemotherapy (PC). However, the COVID-19 pandemic caused a three-year suspension of PC. We conducted a nationwide geostatistical impact assessment to estimate prevalence at ward-level and evaluated impact of PC interruption relative to 2018 results using a quasi-experimental design.

METHODS

The cross-sectional survey in 2021 targeted 11,600 school-aged children (SAC) and sub-sets of pre-SAC and adults. Sampling was optimised to achieve 90% correct classification of wards (N = 1,961) using geostatistical predictions from 2018 impact data. 200 schools were selected with inclusion proportional to predicted Schistosoma haematobium prevalence. All SAC provided urine and stool samples analysed by urine filtration and Kato-Katz. Geostatistical models incorporating environmental covariates were fitted and used to generate high-resolution prevalence predictions.

RESULTS

Data from 11,190 participants indicated a national schistosomiasis prevalence of 7.0% (95% CI 5.0-9.8%) including focal recrudescence of S. mansoni. Heavy-intensity infection recrudesced above 1% EPHP threshold (1.4%, 95% CI 0.9-2.0). STH prevalence increased though remained low (1.4%, 95% CI 1.0-2.1%), with few moderate-heavy infections (< 0.1%, 95% CI < 0.1-1.2). Geostatistical predictions delineated key spatial heterogeneity: 98.9% of wards exceeded 2% schistosomiasis prevalence (17,909,432 people), 37.2% required annual PC (≥ 10% prevalence; 6,473,455 people), and 33.4% wards exceeded 2% prevalence for STH (biennial PC).

CONCLUSIONS

PC suspension led to recrudescence of schistosomiasis and smaller increases in STH prevalence. These findings emphasise the risk of pausing PC even in low or moderate prevalence settings. Continued surveillance and tailored PC are essential to achieve 2030 goals, with geostatistical outputs supporting precision interventions.