Background
WHO-recommended prevalence thresholds for deciding schistosomiasis mass drug administration (MDA) are based on anecdotal evidence and unclear.
Objectives
This systematic review and meta-analysis commissioned by the WHO, as part of its new schistosomiasis evidence-based guideline development, was to generate a single and global prevalence threshold that should be applied in MDA programmes.
Methods
We searched several databases from 1979 to 31st March 2021 without language restriction. Two reviewers selected studies, extracted data and assessed the risk of bias using relevant risk of bias tools and resolved disagreements through discussion. The review followed the PRISMA guidelines. Data were analysed and presented as prevalence reduction (PR) and relative risk (RR) for dichotomous outcomes or mean difference for continuous outcomes with their 95% confidence intervals (CIs). Meta-regression of observations on prevalence rates and intensity of infection of MDA programmes and sensitivity analyses to assess the robustness of the results to the risk of bias components were performed. Evidence on benefits, harms, values, preferences, compliance, acceptability, equity and feasibility were also assessed. The overall level of evidence was graded using GRADE.
Results
Out of 1,232 studies retrieved, 38 studies met our inclusion criteria and 34 studies were included in the meta-analysis. No direct relation was observed between prevalence and intensity of infection. Praziquantel reduced prevalence of S. haematobium in school age children (SAC) at 12 months (RR 0.38, 95% CI 0.28 to 0.52; 8 studies, n=37,868); at 24 months (RR 0.30; 95% CI 0.30 to 0.52; 7 studies; n=37107); at 36 months (RR 0.39, 95% CI 0.21 to 0.71; 5 studies, n=28,146). There was no significant reduction in prevalence at 48 months (2 studies, n=10,954). For S. mansoni, there were reductions in prevalence at 12 months (RR 0.56, 95% CI 0.46 to 0.69; 14 studies, n=86,073); 24 months (RR 0.46; 95% CI 0.32 to 0.66; 14 studies; n=83,721);36 months (RR 0.44, 95% CI 0.33 to 0.58; 7 studies, n=70,933) and at 48 months (RR 0.25, 95% CI 0.11 to 0.59; 5 studies; n=27,483). Further analyses were performed from a series of created prevalence thresholds of 5%, 10%, 15%, 20%, 30% and ≥40% which showed differences in effect of MDA when each of the thresholds was applied. For annual MDA of school age children (SAC), school-based treatment (SBT) appears to perform better than community-wide treatment (CWT) in terms of prevalence reduction. For the different schistosome species, the model suggests, using the same prevalence threshold, it will take shorter time to reach elimination for S. haematobium than S. mansoni; annual MDA using SBT approach for S. haematobium will require about 10 years to achieve elimination whereas it will take over 10 years to around 15 years to achieve elimination for S. mansoni.
Conclusion
The evidence presented in this systematic review suggests that 10% prevalence should be used as the global prevalence threshold for implementing MDA in endemic countries.
Helminth infections and micronutrients in school-age children: a systematic review and meta-analysis
