Authors

Discussion

Background

Schistosomiasis is a water-borne parasitic disease but the relationship between water contact and the likelihood of schistosome infection remains poorly quantified.

Methods 

We conducted a systematic review in accordance with the PRISMA guidelines to estimate the average effect of water contact duration, frequency, and activities on schistosome infection likelihood. We searched Embase, MEDLINE (including PubMed), Global Health, Global Index Medicus, Web of Science, and the Cochrane Central Register of Controlled Trials from inception until May 13, 2022. Observational and interventional studies reporting odds ratios (OR) or hazard ratios (HR) of associations between exposure and schistosome infection were eligible for inclusion. Random-effects meta-analysis with inverse variance weighting was used to calculate pooled ORs and 95% confidence intervals (CIs).

Results  

We screened 1,411 studies and included 101 studies representing 192,691 participants across three continents. Included studies mostly reported on the type of water contact activities (69%; 70/101) and current or past history of having any water contact (33%; 33/101). A meta-analysis of 33 studies showed that individuals with water contact were 3.14 times more likely to be infected compared to individuals with no water contact. Subgroup analyses showed that the positive association of water contact with infection was significantly weaker in children compared to studies which included adults and children (OR 1.67; 95% CI: 1.04–2.69 vs. 4.24; 95% CI: 2.59–6.97). An association of water contact with infection was only found in communities with >10% schistosome prevalence. Overall heterogeneity was substantial (I²=93%) and remained high across all subgroups, except in direct water contact observation studies (I² range=44%–98%). We did not find that occupational water contact such as fishing and agriculture (OR 2.57; 95% CI: 1.89–3.51) conferred a significantly higher risk of schistosome infection compared to recreational water contact (OR 2.13; 95% CI: 1.75–2.60) or domestic water contact (OR 1.91; 95% CI: 1.47–2.48). Higher duration or frequency of water contact did not significantly modify infection likelihood. Study quality across analyses was largely moderate or poor.

Conclusions 

Any current water contact was robustly associated with schistosome infection status across all age groups and areas with >10% prevalence. More research is needed to understand interactions of water contact with age and gender and their influence on infection likelihood. Our results imply the need for population-wide treatment and prevention strategies in endemic settings as exposure within these communities was not confined to currently prioritised high-risk groups such as fishing populations.