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Water, sanitation and hygiene for theprevention of diarrhoeaSandy Cairncross,1� Caroline Hunt,1 Sophie Boisson,1 Kristof Bostoen,1 Val Curtis,1 Isaac CH Fung2

and Wolf-Peter Schmidt1

1London School of Hygiene & Tropical Medicine, Department of Infectious & Tropical Diseases, London, UK and 2Department ofEpidemiology and Biostatistics, College of Public Health, University of Georgia, Athens, GA, USA.

�Corresponding author. London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK.E-mail: [email protected]

Background Ever since John Snow’s intervention on the Broad St pump, theeffect of water quality, hygiene and sanitation in preventingdiarrhoea deaths has always been debated. The evidence identifiedin previous reviews is of variable quality, and mostly relates tomorbidity rather than mortality.

Methods We drew on three systematic reviews, two of them for theCochrane Collaboration, focussed on the effect of handwashingwith soap on diarrhoea, of water quality improvement and ofexcreta disposal, respectively. The estimated effect on diarrhoeamortality was determined by applying the rules adopted for thissupplement, where appropriate.

Results The striking effect of handwashing with soap is consistentacross various study designs and pathogens, though it depends onaccess to water. The effect of water treatment appears similarlylarge, but is not found in few blinded studies, suggesting that itmay be partly due to the placebo effect. There is very little rigorousevidence for the health benefit of sanitation; four interventionstudies were eventually identified, though they were allquasi-randomized, had morbidity as the outcome, and were inChinese.

Conclusion We propose diarrhoea risk reductions of 48, 17 and 36%,associated respectively, with handwashing with soap, improvedwater quality and excreta disposal as the estimates of effect for theLiST model. Most of the evidence is of poor quality. More trials areneeded, but the evidence is nonetheless strong enough to supportthe provision of water supply, sanitation and hygiene for all.

Keywords Water, sanitation, hygiene, diarrhoea, mortality

BackgroundIt has been estimated, at least for Africa, that 85% ofthe burden of disease preventable by water supply iscaused by feco-oral, mainly diarrhoeal diseases,largely due to the substantial child mortality which

they cause.1 In 1854, Dr John Snow famouslyincriminated the water from the Broad St pump asthe vehicle of cholera transmission in London’sSoho, but much of the medical establishmentcontinued to uphold the miasma theory for manyyears thereafter. Ever since then, the role of

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/

by-nc/2.5/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Published by Oxford University Press on behalf of the International Epidemiological Association.

� The Author 2010; all rights reserved.

International Journal of Epidemiology 2010;39:i193–i205

doi:10.1093/ije/dyq035

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water in diarrhoea transmission and preventionhas been hotly debated. More recently, awarenesshas also grown about the importance of excretadisposal in preventing diarrhoeal disease, culminatingin the recent poll of readers of the BritishMedical Journal in which sanitation was voted thegreatest advance in public health in the last century.2

There is strong temptation to conduct evaluationsof the health impact of water supply, sanitation andhygiene interventions, but the challenges also aremany. Often it is difficult or impossible to randomizeor to blind the intervention. In practice, most studiesdo not identify specific aetiologies and so deal with anoutcome (diarrhoea) which is caused by variouspathogens, transmitted by various routes and asso-ciated with various potential confounding factors.The vulnerability of such studies to confounding iscompounded by the use of observational studydesigns and the low relative risks (RRs) involved,which are typically less than two. In developing coun-tries, most episodes of diarrhoea morbidity—evenmuch of the life-threatening morbidity—are notreported to the health system, so that active surveil-lance involving home visits is used to detect them,often with excessive recall periods. In the circum-stances then, it is not surprising that the first meth-odological review of this literature3 located some 50epidemiological studies, but found serious flaws inevery one.

A series of literature reviews conducted by Esreyand others4–7 established a consensus view on theimpacts on health of improved water quality, waterquantity and sanitation, which was summarized inthe relevant chapter of Disease Control in DevelopingCountries.8 A more recent review9 gave prominence toa number of studies of household-based watertreatment, and arrived at a greater estimate ofthe impact of water quality than previous reviews.However, the confidence intervals (CIs) for thisand the other such estimates were very wide, sowide as to show that the new figures were notsignificantly different from the corresponding previousestimates.

In this article, drawing on three systematicreviews of the literature, we present the evidence foran impact on diarrhoea mortality from improvementsin hygiene (specifically, handwashing with soap),10

drinking-water quality,11 and excreta disposal. Thereviews of effectiveness of the interventions areshaped in large part by the needs of the LiST model.In that model, increases in coverage of an interven-tion result in a reduction of deaths due to one ormore causes or in the reduction of a risk factor.Therefore, the reviews and the grade process usedwere designed to develop estimates of the effectof an intervention in reducing either a risk factor ordeaths due to a specific cause. For more details ofthe review methods, the adapted grade approach orthe LiST model, see other articles in this supplement.

MethodsHandwashing with soapThe original review10 aimed to identify all studiespublished in English up to the end of 2002 relatinghandwashing to the risk of infectious intestinal ordiarrhoeal diseases in the community. Medline, CABAbstracts, Embase, Web of Science and the CochraneLibrary were systematically searched for papersrelated to handwashing, use of soap, as well as dis-ease terms such as diarrhoea, typhoid, enteric, chol-era, shigellosis, dysentery, and mortality. Searcheswere also undertaken by hand with reference listsfrom these papers, the authors’ own collections andreview articles. No limitations were placed on date orgeographical location. The search was updated in2008.

Studies were retained for the meta-analysis if theyprovided point estimates and 95% CIs (or the meansto calculate them) of the risk of not washing hands.Intervention trials not solely concerned with hand-washing were excluded. Where both crude andadjusted odds ratios were presented, adjusted valueswere used. The risk values for studies with severalmeasures of handwashing practice were combinedby averaging, if they concerned the same samplegroup. If they concerned different groups, they weretreated as if they were separate studies. Similarly,studies with two different outcome measures wereentered into the meta-analysis as if they were sepa-rate studies.

Water qualityFollowing the Cochrane peer-reviewed protocol,12 wesearched the specialized register of the CochraneInfectious Diseases Group, CENTRAL, Medline,Embase and LILACS for all randomized andquasi-randomized controlled trials of interventions toimprove water quality for the prevention of diarrhoealdisease, regardless of language, publication status, ordate, up to December 2005. Interventions includedany measure to improve the microbial quality ofdrinking water, unless undertaken in response to epi-demic diarrhoea. The primary outcome was diarrhoeain adults or children. We hand searched conferenceproceedings, contacted researchers and organizationsworking in the specialty, and checked the referencesof identified studies. Two reviewers independentlyexamined the electronic records for potentially eligiblestudies and the full text of potentially eligible reports.Disagreements were resolved by a third reviewer.

Measures of effect reported were risk ratios, rateratios, odds ratios and longitudinal prevalence ratios(number of days or weeks with diarrhoea divided bynumber of days or weeks under observation in aperson). The results are presented separately bystudy type and also by type of intervention, whethersource- or household-based. A random effects inverse

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variance method was used on the log scale to calcu-late pooled estimates.

Excreta disposalAgain we followed the Cochrane approved protocol13

to search for interventions to dispose of humanexcreta so as to reduce direct or indirect human con-tact. This includes any steps to remove or containfaeces, such as simple pit latrines, bucket latrines,hanging toilets and composting toilets, and shouldbe contrasted with open defecation. Diarrhoea wasagain the outcome measure, whether or not microbio-logically confirmed. We defined diarrhoea and anepisode in accordance with the case definitions usedin each trial. We excluded trials that had no clinicaloutcomes; for example, trials that only reported onmicrobiological pathogens in the stool.

We searched the following databases up to April2007: Cochrane Infectious Disease Group SpecializedRegister; CENTRAL; MEDLINE; EMBASE; LILACS,and also Chinese-language databases available underthe Wan Fang portal using the Chinese equivalents ofour search terms where appropriate. We searched themetaRegister of Controlled Trials (mRCT) using ‘diar-rhea’, ‘diarrhoea’ and ‘sanitation or latrine or toilet orprivy or disposal’ as search terms, and also a number ofrelevant conference proceedings. Other researchers andrelevant international agencies were also contactedin the search for unpublished and ongoing trials. Thereference lists of studies identified as above were alsoscanned for any further relevant studies.

GeneralAll studies which met final inclusion and exclusioncriteria were double data abstracted into a standar-dized form for each outcome of interest.14 Weabstracted key variables with regard to the studyidentifiers and context, study design and limitations,intervention specifics, and outcome effects. Eachstudy was assessed and graded according to the adap-tation by the Child Health Epidemiology ReferenceGroup (CHERG) of the GRADE technique.15 Studiesreceived an initial score of high if a randomized orcluster randomized trial. The grade was decreased onegrade for each study design limitation. In addition,studies reporting an intent-to-treat analysis or withstatistically significant strong levels of association(480% reduction) receive 1–2 grade increases. Anystudy with a final grade of very low was excludedon the basis of inadequate study quality. The processis summarized in Tables 1, 2 and 3. To save space, wehave not listed all of the studies in all three reviewswith the bibliography of this article; instead, adetailed listing is provided in three correspondingSupplementary Tables 1, 2 and 3 available at IJEonline. The numbers in Tables 1, 2 and 3 refer tothese supplementary tables.

For the outcome of interest, namely the reductionof diarrhoea mortality, we applied the CHERG Rules

for Evidence Review14 to the collective diarrhoea mor-bidity and mortality outcomes to generate a finalestimate of effect.

ResultsHandwashing with soapThe search identified a total of 38 studies (Figure 1) but21 were not suitable for data extraction, either becausethey did not specify whether soap was used, or did notpresent data permitting a calculation of effect. Of the17 remaining studies, 7 were intervention trials and10 were observational (Table 1). All of the interven-tions or exposure measures related to handwashingbefore eating or food handling, or after defecation orhandling of child stools, or a combination of these.

Only one mortality study was found.16 The numberof events was not stated, but the wide confidenceintervals (reduction of þ62% to �43%) suggest therewere very few, and the study was observational, withweaknesses in the outcome definition (deaths fromother infectious diseases besides diarrhoea wereincluded) and ascertainment of compliance.

We therefore turned to morbidity studies. None ofthe intervention studies gave adequate compliancedata, so that the effect reported (a reduction of47%) is that of handwashing promotion rather thanof handwashing itself; i.e. the effect of the interven-tion, not the individual’s response to it. However, thiswas slightly greater than the pooled effect (a reduc-tion of 43%) of all studies in the review (Figure 2aand b). In other words, the observational studies,which did report the effect of individuals’ behaviour,did not find a greater effect. The original reviewfound that the effect was remarkably consistentacross studies of higher methodological quality, andstudies with severe forms of diarrhoea as an outcome.In each of these categories, the pooled estimate ofeffect is of a reduction within the range of 42–48%(Table 1). The combined effect of the more severediarrhoeas was a 48% reduction. Two studies oflaboratory confirmed shigellosis,17,18 a more severeand a ‘harder’ outcome than self-reported diarrhoea,had a pooled effect of reduction by 59%. On the otherhand, three studies were conducted in settings wherewater use was known to be constrained; (i) alow-income area of Lima, Peru, where vendors sellwater expensively from tanker trucks, (ii) a refugeecamp in Malawi and (iii) a setting in Burundi wheremedian water usage was only 5 l per capita per day.The reductions in risk were 11, 26 and 41%, respec-tively, all of them less than the combined effect of43% found in the review as a whole.

Subsequent to our initial review,10 a Cochranereview of the effect of handwashing on diarrhoeawas published.19 Most of the studies included werein institutional settings, but five were conducted inthe community. In two of those, the intervention

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did not involve soap and was not focussed on hand-washing. Pooling the other three20–22 gave a reductionin diarrhoea by 43% (95% CI 25–56%).

Water quality interventionsTwo studies with a mortality outcome were found andincluded, following the Cochrane protocol12

(see Figure 3 and Table 2). One of these23 had ascer-tained diarrhoea mortality, but the interventionincluded health education about oral rehydrationtherapy for diarrhoea, which alone could explain the85% reduction in diarrhoea mortality that wasobserved. Moreover, only two villages had been ran-domized. The other trial,24 whose authors admit thatit was not designed to detect a mortality outcome,found a significant reduction (RR of death¼ 0.58,P < 0.036) only for all causes and all ages by poolingtwo intervention arms (total 59 events). Pooling thestudies would be questionable, as the interventionswere very different.

The serious limitations of the mortality studies ledus to consider the morbidity studies. All took self-reported diarrhoea as the outcome; the Cochraneprotocol had excluded trials that had no clinical out-comes, such as trials that report only on microbiolo-gical pathogens in the stool. Similar results wereobtained for diarrhoea in all age groups and withthe outcome limited to children aged <5 years. Thetype of study seemed to have little bearing on themeasure of effect, which ranged from 46% in rando-mized controlled trials (RCTs) to 38% of quasi-RCTs.The review protocol approved by the CochraneCollaboration had limited its scope to trials, so thatno observational studies were included. Interventionsbased at the water source had less effect (27% for allages, 15% for young children) than household-basedones, with an effect of 43–44%, depending on the agerange. Two studies implemented in settings wherethe water before treatment had <10 faecal coli-forms/100 ml (a concentration classified by WHO as

17 suitable for data extraction

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Figure 1 Synthesis of study identification in review of theeffect of handwashing with soap on diarrhoea mortality andmorbidity10

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Figure 2 Forest plots of (a) all studies in handwashing review, and (b) intervention studies only. Numbers on y-axis arereferences to studies in Supplementary Table 1. The diamond represents the combined relative risk and 95% CI fromrandom effects model10


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‘low risk’) had a combined effect of reducing risk by61% (95% CI 30–67%) with insignificant heterogene-ity. The greatest difference of all was between the 31unblinded and the 4 blinded trials,25–28 with the lattergiving a reduction of only 7% in diarrhoea risk, whichwas not statistically significant (Figure 4).

Excreta disposalOur initial attempt at this review nearly foundered.The initial search13 produced seven quasi-randomizedintervention studies with diarrhoea morbidity as theoutcome measure, and one with diarrhoea mortality(Figure 5, Table 4). The mortality study has alreadybeen mentioned;23 the intervention included watersupply and education about oral rehydration therapy,which could explain the observed reduction in mor-tality. All eight studies involved an intervention toimprove water supply as well as excreta disposal, sothat in none of them is it possible to assess the impactof sanitation as an intervention per se.

A renewed effort to locate suitable studies produceda further four,29–32 in which the intervention involvedexcreta disposal alone. All four were conducted inChina (see the following URL http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&msid=109120590372693546058.000465c8157b73053ba7f&z=6for a map of the study sites), and published inChinese (Table 3). The reductions in diarrhoea mor-bidity in the four studies were 63, 51, 20 and 8%,respectively. In all but the last, the confidence intervaldid not include zero reduction. We did not calculatepooled estimates for the sanitation trials, because

most studies randomized a very small number of vil-lages, which makes calculation of confidence intervalsimpossible. Also, the interventions tested were verydifferent from one another, which also makes poolingquestionable.

These four studies are hardly ideal; they arequasi-randomized, not full RCTs; the control groupsdid not lack sanitation altogether, but mainly usedsome sort of pit latrine; and third, the published stu-dies are not available for scrutiny except by those ableto read Chinese. We therefore widened our scopefurther to include before/after studies. The unit ofintervention is effectively the community, neighbour-hood or village, but only one such study consideredenough such units for statistical tests to be applied atthis level. This recent study33 is, strictly speaking, abefore/after design, but is in many ways akin to a

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Figure 4 Forest plots of (a) all 35 studies in water qualityreview, and (b) the four blinded studies only35

41 trials from 32 studiesincluded in meta-analysis

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38 excluded33 met inclusion criteria 4 had 2 trial arms 1 had 3 trial arms 1 had 4 trial arms- yielding 42 included trials

1 excluded frommeta-analysis;inadequateinformation

979 relevant studies identified: 939 by database search 40 by hand

Figure 3 Synthesis of study identification in review of theeffect of water quality interventions on diarrhoea mortalityand morbidity11


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quasi-randomized trial in 24 neighbourhoods of theCity of Salvador, Brazil. It found a city-wide reductionof 21% (95% CI 19–26%), and 43% (CI 39–46%) in thehigh risk areas.

DiscussionHandwashing with soapOnce the nature of the studies has been consistentlydefined (in the present case, community-based stu-dies with an intervention focussed on handwashingand involving soap), the studies in the literature areremarkably consistent, showing a reduction in diar-rhoea by 42–48%. We took 48%, the reduction foundfor the more severe diarrhoeas, as the figure to pro-pose for LiST.

The problem encountered with water quality inter-ventions, that the blinded studies do not support thepositive picture drawn by the others, raises the ques-tion of whether this problem applies to handwashingwith soap. After all, one cannot persuade people towash their hands without their knowledge! The dif-fering results of the blinded and unblinded studiessuggest that much of the apparent impact of watertreatment is attributable to bias, but by the sametoken that possibility cannot be ignored in the caseof handwashing.

Blinding can be applied to two groups; the subjects,and those who assess their status. It can refer to eachsubject’s exposure allocation, or to the nature of theexposure or the disease outcome. Indeed, theCochrane review of handwashing19 noted that one

7 trialsincluded in CHERGreview

45 excluded onbasis of abstract

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8 excluded12 trials met inclusion criteria (outcomes included diarrhoeal disease, helminth infestations and schistosomiasis)

5 excluded as outcomes were other than diarrhoea

65 relevant studies identified

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study34 had used a placebo intervention to concealfrom the subjects and assessors which was the inter-vention group and which the control, and had founda smaller effect than the other community-basedtrials. An alternative explanation is that this studydid not focus on handwashing or provide soap. Allof the community-based trials which did not focuson handwashing or provide soap found smaller reduc-tions in diarrhoea than either of those which didthose things. Of the less focussed group, the partiallyblinded study34 found a reduction of 6% (95%CI: �44–15%) while the other, open trial of thiskind35 found 25% (95% CI 15–34%) so the lack ofblinding seems to explain at least part of the differ-ence. Of course, such non-focussed trials wereexcluded from our earlier review,10 and none of theintervention studies focussed on handwashing (Figure2a) used a placebo intervention. The consistency ofeffect between observational and intervention studiesled us to judge that the effect is probably genuine, butmore research is needed to clarify this point.

Water quality interventionsEnthusiasts for point-of-use household-based watertreatment argue that the smaller effect ofsource-based interventions is due to subsequent con-tamination of the water on its way to, or during stor-age in the household. Sceptics point to the lack ofsignificant effect found in the blinded studies, attri-buting the difference to courtesy bias or placeboeffect. They suggest that consumers are less consciousof treatment administered centrally, and so less likelyto show these forms of bias in their self-reporting ofdiarrhoea.

These findings have given rise to a lively debateabout the desirability of scaling-up household-basedwater treatment.36,37 The only certain conclusion isthat the implications are uncertain, and it is unlikelythat a Delphi process would arrive at an amicableconsensus.

There are several reasons to believe that the biasmay apply to water quality but which are less appli-cable to handwashing. First, there is biological plau-sibility; in many settings, a subject would have toingest very large amounts of water in order to

consume an infectious dose of a bacterial pathogen.Second, the anomaly that the reduction in diarrhoeaseems to be independent of the quality of the ambientwater before it is treated. Third, the observationalstudies of drinking-water quality (e.g. see ref.38) donot show such large effects as the point-of-use inter-vention trials. And fourth, most of these trials werefunded by manufacturers of water treatment chemi-cals or equipment.

In these circumstances the data from the recentspate of trials—and hence, any systematic reviewbased on them—do not offer a firm basis for judgingthe effect of water quality improvements. The optionsinclude adopting the effect of the four blinded trials(no significant reduction in any trial), adopting thepooled effect of the source-based intervention studies(three trials among children under five gave a 7%reduction), or keeping the pre-existing consensusview arrived at two decades ago in reviews of obser-vational and source-based intervention studies,4,7 thatwater quality improvements can be expected to beassociated with a reduction of some 17% in diarrhoearisk. This latter figure was proposed for LiST as asso-ciated with use of an improved water supply, which isavailable within a reasonable distance, requiring areturn journey of 30 min or less.

One theme which emerged from the debate was that‘harder’ outcomes such as care-seeking for diarrhoeawould be more objective and less prone to bias than arelatively ‘softer’ outcome such as self-reported diar-rhoea. One well-known water quality trial,39 excludedfrom our review because the outcome included gastro-enteritis without diarrhoea, found that during thestudy period ‘the number of visits to physicians forgastrointestinal symptoms and of hospitalizations wassimilar in both groups.’ In this context, one recenttrial with both handwashing and water qualityarms40 is of particular interest, as the authors docu-mented the effect of each arm both in terms ofself-reported diarrhoea and of care-seeking (seeTable 5). The effect of each intervention is very sim-ilar, whichever the outcome. This suggests, either thatany bias affecting the former outcome also affectedthe latter; or that the former was not susceptible tobias as the blinded studies suggest.

Table 5 Comparison of effects of (i) promotion of hand washing with soap, and (ii) household water treatment, measuredin terms of weekly prevalence of diarrhoea, and of frequency of consulting a practitioner for treatment for diarrhoea22

Intervention group Reduction in weeklyself-reported diarrhoeaprevalence (95% CI)

Reduction in care-seekingfor diarrhoea in children<5 years (95% CI)

Soap and hand washing promotion 45% (12–68%) 48% (15–71%)Bleach water treatment 53% (22–75%) 54% (22–77%)Flocculant-disinfectant water treatment 59% (29–82%) 61% (31–84%)Flocculant-disinfectant plus hand washing with soap 50% (18–72%) 55% (23–77%)


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Excreta disposalIt is in this area that the evidence is weakest. It is notsurprising that trials are few, as provision of hundredsof latrines is expensive. Observational studies cannotbe trusted, in view of evidence that people inlatrine-owning households (a self-selected group)behave more hygienically than others, even inrespects which have nothing to do with excreta dis-posal.41,42 This is not to say that excreta disposal hasno effect on diarrhoea. Indeed, there is a striking con-sistency between the reductions found in variousreviews of 36%,7 32%,9 20–51% (the four Chinese stu-dies) and 22–43%.33 That being so, there is notenough evidence to justify a departure from the pre-vailing consensus, published nearly two decades ago7

and widely cited with approval since then, that sani-tation reduces diarrhoea risk by about 36%. This thenis the strength of effect proposed for the LiST model.

GeneralThe lack of conclusive evidence of the effect on diar-rhoea of improvements in water, hygiene and sanita-tion in developing countries is not an excuse forinaction.43 We know enough to do a lot of good. Inspite of doubts about the detail, it is clear that suchenvironmental interventions can have a substantialeffect on diarrhoea morbidity, and the very few rele-vant studies44 confirm that they have a similar effectupon diarrhoea mortality. Moreover, water, hygieneand sanitation have other important benefits, includ-ing the emancipation of women from drudgery andthe enhancement of human dignity, and even otherhealth benefits such as the control of trachoma and ofintestinal helminths.

It is not entirely surprising that the evidence isweak; studies of mortality are fraught with ethicaland logistic problems; water supplies and sanitationare expensive interventions to trial; and the engineerswho install them are not accustomed to trials as animportant part of their professional culture. Moreover,it is particularly difficult to blind a trial of an inter-vention involving the provision of hardware or thepromotion of behaviour change, and as we have

seen, it appears that the lack of blinding can lead tosubstantial bias if the outcome is ‘soft’.

In the context of a literature of uneven quality suchas this, these reviews can also teach us that there isno definitive systematic review, or objective set ofrules for conducting one. The examples here showhow the result of a systematic review depends upona number of questions, such as the definition of theoutcome (should only diarrhoea be accepted, andvomiting rejected?), of the intervention (is seweragein Brazil different from pit latrines in Africa?), on therange of languages accepted (in several recentreviews,13,45 more than a third of useful studieswere in Chinese) and on which are regarded as thegravest methodological deficiencies. Each of thosequestions has more than one reasonable answer.Judgement-free data are a myth.

Supplementary dataSupplementary data are available at IJE online.

FundingThe US Fund for UNICEF from the Bill & MelindaGates Foundation (grant 43386, partially) to‘Promote evidence-based decision making in design-ing maternal, neonatal and child health interventionsin low- and middle-income countries’ and UNICEF,Unilever research and WaterAid.

AcknowledgementsStimulating discussions with colleagues in the CHERGhave helped to improve this article; their input isgratefully acknowledged. So are the major contribu-tions of Tom Clasen as principal author of the reviewson water and on sanitation, the patient and construc-tive support of Therese Dooley and the administrativewizardry of Eileen Chappell.

Conflict of interest: None declared.

KEY MESSAGES

� Effect of handwashing with soap is most consistent at roughly 48% reduction in diarrhoea.

� Effect of water quality improvements found in RCTs seems to be affected by bias – not seen inblinded studies.

� Evidence for effect of sanitation is weakest – randomized trials are needed – but may be 36%reduction.

� Though evidence is weak compared with clinical RCTs, it is enough for action.

� Analysing such evidence needs more than algorithms – it requires judgement.


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