Interventions to improve water, sanitation, and hygiene for preventing soil‐transmitted helminth infection

21 Jun 2022

What is the aim of this review?

This review summarizes randomized controlled trials (RCTs) (studies where participants are randomly assigned to one of two or more treatment groups) and non‐randomized trials (non‐RCTs) evaluating the effect of water, sanitation, and hygiene interventions on preventing soil‐transmitted helminth infections. 

Soil‐transmitted helminths (STHs) comprise a group of intestinal parasites that are transmitted to humans through ingestion of infective eggs or transcutaneous (through the skin) penetration of larvae excreted in human faeces which contaminate the soil and water sources. Even with deworming efforts, re‐infection occurs rapidly, and interruption of transmission is unlikely without complementary control efforts. Environmental improvements, such as access to and use of safe and adequate water, basic sanitation, and hygiene (WASH), is thought to be essential to sustain reductions in re‐infection and to reduce illness.

Key messages

The evidence suggests that the WASH interventions under study may slightly reduce STH infection. Many of these results were in studies coupled with mass drug administration in both the treatment arm(s) and the control arm, and therefore show the impact of WASH on STH infection above and beyond the application of mass drug administration alone.

What was studied in the review?

Previous reviews assessing WASH and STH infection have relied heavily on non‐experimental studies. We investigated rigorous, experimental evidence assessing the role of WASH programmes to reduce STH infection.

What are the main results of the review?

We searched the scientific literature for relevant studies (published, unpublished, in press, and ongoing) up to 19 October 2021 and identified 32 studies (16 RCTs and 16 non‐RCTs) enrolling a total of 52,944 participants. We found evidence that the WASH interventions under study may result in a slight reduction of any STH infection. Pooling of 14 RCTs for analysis of this outcome showed a slightly lower (14%) odds of any STH infection amongst participants in the WASH group compared to those in the control group. Similarly, pooling of eight non‐RCTS for analysis of any STH infection showed that the odds of any STH infection was 29% lower amongst participants in the WASH group compared to the control group. When considering the analyses assessing WASH interventions on individual worm species, the evidence was very uncertain; WASH interventions may result in little to no reduction in Trichuris trichiura infection and may result in a slight reduction in Ascaris lumbricoides and hookworm infection. Data on intensity of infection (e.g. faecal egg count) were reported in a variety of ways across studies, preventing the pooling of results for this outcome.

How up‐to‐date is the evidence?

The evidence is current to 19 October 2021.