The relationship between water, sanitation and schistosomiasis: a systematic review and meta-analysis

Abstract

Background: Access to "safe" water and "adequate" sanitation are emphasized as important measures for schistosomiasis control. Indeed, the schistosomes' lifecycles suggest that their transmission may be reduced through safe water and adequate sanitation. However, the evidence has not previously been compiled in a systematic review.

Methodology: We carried out a systematic review and meta-analysis of studies reporting schistosome infection rates in people who do or do not have access to safe water and adequate sanitation. PubMed, Web of Science, Embase, and the Cochrane Library were searched from inception to 31 December 2013, without restrictions on year of publication or language. Studies' titles and abstracts were screened by two independent assessors. Papers deemed of interest were read in full and appropriate studies included in the meta-analysis. Publication bias was assessed through the visual inspection of funnel plots and through Egger's test. Heterogeneity of datasets within the meta-analysis was quantified using Higgins' I2.

Principal findings: Safe water supplies were associated with significantly lower odds of schistosomiasis (odds ratio (OR) = 0.53, 95% confidence interval (CI): 0.47-0.61). Adequate sanitation was associated with lower odds of Schistosoma mansoni, (OR = 0.59, 95% CI: 0.47-0.73) and Schistosoma haematobium (OR = 0.69, 95% CI: 0.57-0.84). Included studies were mainly cross-sectional and quality was largely poor.

Conclusions/significance: Our systematic review and meta-analysis suggests that increasing access to safe water and adequate sanitation are important measures to reduce the odds of schistosome infection. However, most of the studies were observational and quality was poor. Hence, there is a pressing need for adequately powered cluster randomized trials comparing schistosome infection risk with access to safe water and adequate sanitation, more studies which rigorously define water and sanitation, and new research on the relationships between water, sanitation, hygiene, human behavior, and schistosome transmission.

Figure 1. Flow diagram demonstrating identification, inclusion and exclusion of studies.

Figure 2. Forest plot for Schistosoma infection according to availability or use of a safe water source.

Studies on S. haematobium are grouped at the top in blue, followed by those on S. japonicum in red, and those on S. mansoni in green. The square sizes represent the weight given to each dataset, and the black horizontal lines represent 95% confidence intervals. For each species the rhombus is centred on the combined effect size, and its width represents the 95% confidence interval. I² estimates are presented beneath each combined effect size (except for S. japonicum, since two studies is insufficient for the I² calculation). The combined effect size for all human schistosome species is presented at the bottom.

Figure 3. Forest plot for S. mansoni infection according to access to adequate sanitation.

The square sizes represent the weight given to each dataset, and the black horizontal lines represent 95% confidence intervals. The rhombus is centred on the combined effect size, and its width represents the 95% confidence interval. The I² estimate is presented beneath the combined effect size.

Figure 4. Forest plot for S. haematobium infection according to access to adequate sanitation.

The square sizes represent the weight given to each dataset, and the black horizontal lines represent 95% confidence intervals. The rhombus is centred on the combined effect size, and its width represents the 95% confidence interval. The I² estimate is presented beneath the combined effect size.