School Water, Sanitation, and Hygiene, Soil-Transmitted Helminths, and Schistosomes: National Mapping in Ethiopia

Abstract

Background: It is thought that improving water, sanitation, and hygiene (WASH) might reduce the transmission of schistosomes and soil-transmitted helminths, owing to their life cycles. However, few large-scale studies have yet assessed the real extent of associations between WASH and these parasites.

Methodology/principal findings: In the 2013-2014 Ethiopian national mapping of infections with these parasites, school WASH was assessed alongside infection intensity in children, mostly between 10 and 15 years of age. Scores were constructed reflecting exposure to schistosomes arising from water collection for schools, from freshwater sources, and the adequacy of school sanitation and hygiene facilities. Kendall's τb was used to test the WASH scores against the school-level arithmetic mean intensity of infection with each parasite, in schools with at least one child positive for the parasite in question. WASH and parasitology data were available for 1,645 schools. More frequent collection of water for schools, from open freshwater sources was associated with statistically significantly higher Schistosoma mansoni infection intensity (Kendall's τb = 0.097, 95% confidence interval, CI: 0.011 to 0.18), better sanitation was associated with significantly lower Ascaris lumbricoides intensity (Kendall's τb = -0.067, 95% CI: -0.11 to -0.023) and borderline significant lower hookworm intensity (Kendall's τb = -0.039, 95% CI: -0.090 to 0.012, P = 0.067), and better hygiene was associated with significantly lower hookworm intensity (Kendall's τb = -0.076, 95% CI: -0.13 to -0.020). However, no significant differences were observed when comparing sanitation and infection with S. mansoni or Trichuris trichiura, or hygiene and infection with A. lumbricoides or T. trichiura.

Conclusions/significance: Improving school WASH may reduce transmission of these parasites. However, different forms of WASH appear to have different effects on infection with the various parasites, with our analysis finding the strongest associations between water and S. mansoni, sanitation and A. lumbricoides, and hygiene and hookworm.

Fig 1. Flow diagram demonstrating the calculation of the water score.

Fig 2. Flow diagram demonstrating the calculation of the sanitation score.

Fig 3. Flow diagram demonstrating the calculation of the hygiene score.

Fig 4. Locations within Ethiopia of the schools with WASH data and non-zero mean intensity of infection with A: S. mansoni, B: A. lumbricoides, C: T. trichiura, and D: hookworm.

The number of schools (n) is also provided for each map. Note that some of the schools in these maps were not used in the analyses because their water, sanitation, or hygiene data were incomplete.

Fig 5. School water scores and arithmetic mean intensities of S. mansoni infection.

Kendall’s τ_b statistics, the equation of the least-squares line of best fit, and the number of included schools, are presented in the upper-right corner.

Fig 6. School sanitation scores against their arithmetic mean infection intensities for A. S. mansoni, B. A. lumbricoides, C. T. trichiura, and D. hookworm.

The Kendall’s τ_b statistics, equation of the least-squares line of best fit, and sample size are presented in the upper-right corner of each graph.

Fig 7. School hygiene scores against their arithmetic mean infection intensities for A. A. lumbricoides, B. T. trichiura, and C. hookworm.

The Kendall’s τ_b statistics, least-squares best fit line equation, and sample size are presented in the upper-right corner of each graph.