Diarrhoeal diseases are a major cause of morbidity and mortality in low and middle income countries, especially for children. Because these diseases have a faecal origin, interventions focusing on preventing faecal material from entering the household environment might reduce the prevalence of childhood diarrhoea. Recent reviews have suggested interventions to improve water supply and quality, hygiene and sanitation are effective in reducing diarrhoea risk. However the quality of the evidence is varied and is mostly related to morbidity rather than mortality. To fill this gap the current review sets out to review the evidence on the impact of improvements in water, sanitation and hygiene on reducing the risk of diarrhoea and diarrhoea related mortality.
To assess and synthesise the evidence from studies evaluating the impact of interventions promoting hand washing with soap, water treatment and safe disposal of excreta on morbidity and mortality due to diarrhoea and other intestinal infections.
This is an update and overview of previous systematic reviews. The authors searched for studies evaluating the impact of hand-washing, water quality and excreta disposal on morbidity and mortality due to diarrhoea or related intestinal diseases. To be included, studies had to provide point estimates and at least enough data to allow the estimation of 95 per cent confidence intervals.
The review on hand-washing included any studies in English, regardless of location or date, and was updated in 2008. Searches for the review on water quality were carried out up to the end of 2005 and included all studies, regardless of language, publication status, or date. Searches for the review on excreta disposal were undertaken up to April 2007.
The authors searched various databases such as the Cochrane Library CENTRAL; MEDLINE; EMBASE; LILACS. For excreta disposal interventions, the authors also examined Chinese-language databases available under the Wan Fang portal. For all three reviews, they also checked the reference lists of included papers, carried out hand-searches of relevant literature and contacted experts and researchers in the field.
The authors extracted data from all included studies and used an adapted version of the GRADE technique to assess studies. Studies assessed as being of very low quality were excluded.
Finally, the authors synthesised the evidence on hand washing with soap and water treatment using random-effects meta-analysis. The studies assessing excreta disposal were not suitable for meta-analysis and the authors presented the results of the studies in a table, reporting the percentage reduction in relative risk for each included study.
Theevidence on interventions promoting hand washing with soap suggests a relatively large and consistent effect on reducing diarrhoea. Interventions to improve water quality and sanitary disposal also appear to be effective, but the evidence base is weaker and effects smaller in magnitude. Promoting hand washing with soap lead to a 48 per cent reduction in diarrhoea overall, 17 per cent as a result of better water quality and 36 per cent due to proper disposal of excreta. The latter two values are based on findings from previous reviews of the evidence.
The authors include three systematic reviews and assess evidence from RCTs, quasi-experiments and some observational studies. The studies reviewed were mostly evaluations of interventions in low and middle income countries in Asia, Latin America and Africa but also include some studies in the United States and Australia.
Policy relevant findings:
Effect of hand washing with soap:
- The impact of hand-washing on diarrhoea incidence is consistently positive, though is also dependent on access to water. Hand washing with soap led to a reduction in diarrhoea by 43 per cent overall. The pooled effect on more severe diarrhoea was even higher at 48 per cent.
- The review included 17 studies, including seven randomised controlled trials or quasi-experimental studies and ten observational studies. Only one of the 17 studies examined mortality as an outcome, but the authors found it to be methodologically weak.
Effect of improved water quality:
- The authors found that interventions to treat water and improve water quality led to an overall reduction in the risk of diarrhoea of 17 percent. This effect is higher when the treatment is at a household level compared to when it is made at source. However, the majority of the studies included suffer from methodological weaknesses and as a result the authors call for caution in interpreting the results.
- The result of higher quality blinded studies showed an insignificant impact of water treatment on diarrhoea risk reduction. The authors interpret this as suggesting the findings from previous un-blinded studies may suffer from courtesy bias or placebo effects, and that the effects of water quality interventions therefore are overstated.
- The authors included 41 trials from 32 studies assessing the effects of improved water quality on diarrhoea. Only two trials reported mortality due to diarrhoea.
Effect of excreta disposal:
- Four quasi-experimental studies in China showed a significant effect of improved sanitation on diarrhoeal risk reduction.
- The review included eight studies. Seven of those studies focussed on morbidity as an outcome and one reported on mortality due to diarrhoea. All interventions focussed on water quality and sanitation so the effect is related to both.
- The authors conclude that overall there is lack of good quality evidence in this area. However, they suggest that although the available evidence is weaker, it is still sufficient to indicate the value of undertaking this type of intervention.
Implications for further research:
Further rigorous research in this area is required. The authors suggest there is a need to understand the difference of effect between blinded, partially blinded and non- blinded studies. The authors also suggest a need for further research on intervention studies using placebo for hand washing.