What is the aim of this review?
The aim of this Cochrane Review was to assess if diarrhoea is reduced by sanitation interventions to provide, upgrade, or encourage people to use toilets or latrines. We collected and analysed all relevant studies of certain prespecified rigorous study design types and found 51 studies involving 238,535 people.
Key messages
We found evidence that sanitation interventions may be protective against diarrhoea. However, the effects varied by the type of intervention and setting, and the certainty of the evidence ranged from very low to moderate.
What was studied in this review?
Diarrhoea is a major cause of death and disease, especially amongst young children in low-income countries. Many of the pathogens that cause diarrhoea are transmitted through exposure to human faeces. Sanitation facilities, such as toilets and latrines, serve as a primary barrier to separate pathogens excreted in human faeces from the environment. This review examined intervention studies to improve sanitation access, facilities, or use. We identified 51 studies of such interventions, most of which were from low- or middle-income countries.
What were the main results of this review?
The results suggest that sanitation interventions reduce diarrhoea by about 15% to 26%, both in vulnerable young children and all age populations. However, not all interventions were protective, and effects varied substantially by the type of intervention and setting. We estimated that an intervention to provide sanitation access to people practising open defecation would probably reduce diarrhoea by about 11% to 21%, an intervention to improve existing sanitation facilities may reduce diarrhoea by about 15% to 35%, and a behaviour change intervention to improve sanitation access or use without providing infrastructure or subsidies would probably reduce diarrhoea by about 15% to 18%. However, the certainty of the evidence ranged from moderate to very low, and additional research is likely to change these estimates, particularly for interventions that provide sanitation access or improve existing sanitation facilities. Further research is also necessary to understand which type of interventions would yield the most protective health effects in various types of settings.
How up-to-date is this review?
We searched for studies that had been published up to 16 February 2022.
There is evidence that sanitation interventions are effective at preventing diarrhoea, both for young children and all age populations. The actual level of effectiveness, however, varies by type of intervention and setting. There is a need for research to better understand the factors that influence effectiveness.
Diarrhoea is a major contributor to the global disease burden, particularly amongst children under five years in low- and middle-income countries (LMICs). As many of the infectious agents associated with diarrhoea are transmitted through faeces, sanitation interventions to safely contain and manage human faeces have the potential to reduce exposure and diarrhoeal disease.
To assess the effectiveness of sanitation interventions for preventing diarrhoeal disease, alone or in combination with other WASH interventions.
We searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL, MEDLINE, Embase, LILACS, and Chinese language databases available under the China National Knowledge Infrastructure (CNKI-CAJ). We also searched the metaRegister of Controlled Trials (mRCT) and conference proceedings, contacted researchers, and searched references of included studies. The last search date was 16 February 2022.
We included randomized controlled trials (RCTs), quasi-RCTs, non-randomized controlled trials (NRCTs), controlled before-and-after studies (CBAs), and matched cohort studies of interventions aimed at introducing or expanding the coverage and/or use of sanitation facilities in children and adults in any country or population. Our primary outcome of interest was diarrhoea and secondary outcomes included dysentery (bloody diarrhoea), persistent diarrhoea, hospital or clinical visits for diarrhoea, mortality, and adverse events. We included sanitation interventions whether they were conducted independently or in combination with other interventions.
Two review authors independently assessed eligible studies, extracted relevant data, assessed risk of bias, and assessed the certainty of evidence using the GRADE approach. We used meta-analyses to estimate pooled measures of effect, described results narratively, and investigated potential sources of heterogeneity using subgroup analyses.
Fifty-one studies met our inclusion criteria, with a total of 238,535 participants. Of these, 50 studies had sufficient information to be included in quantitative meta-analysis, including 17 cluster-RCTs and 33 studies with non-randomized study designs (20 NRCTs, one CBA, and 12 matched cohort studies). Most were conducted in LMICs and 86% were conducted in whole or part in rural areas. Studies covered three broad types of interventions: (1) providing access to any sanitation facility to participants without existing access practising open defecation, (2) improving participants' existing sanitation facility, or (3) behaviour change messaging to improve sanitation access or practices without providing hardware or subsidy, although many studies overlapped multiple categories. There was substantial heterogeneity amongst individual study results for all types of interventions.
Providing access to any sanitation facility
Providing access to sanitation facilities was evaluated in seven cluster-RCTs, and may reduce diarrhoea prevalence in all age groups (risk ratio (RR) 0.89, 95% confidence interval (CI) 0.73 to 1.08; 7 trials, 40,129 participants, low-certainty evidence). In children under five years, access may have little or no effect on diarrhoea prevalence (RR 0.98, 95% CI 0.83 to 1.16, 4 trials, 16,215 participants, low-certainty evidence). Additional analysis in non-randomized studies was generally consistent with these findings. Pooled estimates across randomized and non-randomized studies provided similar protective estimates (all ages: RR 0.79, 95% CI 0.66 to 0.94; 15 studies, 73,511 participants; children < 5 years: RR 0.83, 95% CI 0.68 to 1.02; 11 studies, 25,614 participants).
Sanitation facility improvement
Interventions designed to improve existing sanitation facilities were evaluated in three cluster-RCTs in children under five and may reduce diarrhoea prevalence (RR 0.85, 95% CI 0.69 to 1.06; 3 trials, 14,900 participants, low-certainty evidence). However, some of these interventions, such as sewerage connection, are not easily randomized. Non-randomized studies across participants of all ages provided estimates that improving sanitation facilities may reduce diarrhoea, but may be subject to confounding (RR 0.61, 95% CI 0.50 to 0.74; 23 studies, 117,639 participants, low-certainty evidence). Pooled estimates across randomized and non-randomized studies provided similar protective estimates (all ages: RR 0.65, 95% CI 0.55 to 0.78; 26 studies, 132,539 participants; children < 5 years: RR 0.70, 95% CI 0.54 to 0.91, 12 studies, 23,353 participants).
Behaviour change messaging only (no hardware or subsidy provided)
Strategies to promote behaviour change to construct, upgrade, or use sanitation facilities were evaluated in seven cluster-RCTs in children under five, and probably reduce diarrhoea prevalence (RR 0.82, 95% CI 0.69 to 0.98; 7 studies, 28,909 participants, moderate-certainty evidence). Additional analysis from two non-randomized studies found no effect, though with very high uncertainty. Pooled estimates across randomized and non-randomized studies provided similar protective estimates (RR 0.85, 95% CI 0.73 to 1.01; 9 studies, 31,080 participants). No studies measured the effects of this type of intervention in older populations.
Any sanitation intervention
A pooled analysis of cluster-RCTs across all sanitation interventions demonstrated that the interventions may reduce diarrhoea prevalence in all ages (RR 0.85, 95% CI 0.76 to 0.95, 17 trials, 83,938 participants, low-certainty evidence) and children under five (RR 0.87, 95% CI 0.77 to 0.97; 14 trials, 60,024 participants, low-certainty evidence). Non-randomized comparisons also demonstrated a protective effect, but may be subject to confounding. Pooled estimates across randomized and non-randomized studies provided similar protective estimates (all ages: RR 0.74, 95% CI 0.67 to 0.82; 50 studies, 237,130 participants; children < 5 years: RR 0.80, 95% CI 0.71 to 0.89; 32 studies, 80,047 participants). In subgroup analysis, there was some evidence of larger effects in studies with increased coverage amongst all participants (75% or higher coverage levels) and also some evidence that the effect decreased over longer follow-up times for children under five years.
There was limited evidence on other outcomes. However, there was some evidence that any sanitation intervention was protective against dysentery (RR 0.74, 95% CI 0.54 to 1.00; 5 studies, 34,025 participants) and persistent diarrhoea (RR 0.57, 95% CI 0.43 to 0.75; 2 studies, 2665 participants), but not against clinic visits for diarrhoea (RR 0.86, 95% CI 0.44 to 1.67; 2 studies, 3720 participants) or all-cause mortality (RR 0.99, 95% CI 0.89 to1.09; 7 studies, 46,123 participants).