Correspondence Comment on “Household Water Treatment in Poor Populations: Is There Enough Evidence for Scaling up Now?” In their recent paper, Schmidt and Cairncross argue that promotion of household water treatment (HWT) among poor populations is premature (1). The paper makes useful points about the challenge of minimizing bias in assessing diarrheal disease that are relevant to studies of all water, sanitation, and hygiene interventions. However, their particular contention that the evidence does not support scaling up HWT is puzzling, not least because they reached the opposite conclusionsthat it “should be strongly encouraged”sin a 2006 Cochrane review based mainly on the same evidence (2). Moreover, their assertion that HWT has not yet been shown to be acceptable and scalable on a sustained basis is difficult to reconcile with the fact that more than 850 million people in 58 low- and middleincome countries already report usually treating their water at home before drinking it (3). The paper reflects issues that are at the heart of public health decision-making. Most fundamentally, how much evidence is required in order to justify an intervention, while research is continuing to improve our understanding of its effectiveness and how to target coverage and enhance adoption? At face value, treating water at home in locations where that water is polluted with feces makes sense. The fact that fecal contamination of water is a significant health concern has been largely unquestioned since John Snow removed the handle of the Broad Street pump in 1854, and its contemporary relevance is confirmed by ongoing outbreaks of waterborne infectious disease in the developing and developed worlds. The fact that billions of individuals lack safe water is not in question, and the logic of simple measures to empower those households to act to protect their health is compelling. Schmidt and Cairncross do not question the microbiological performance of the intervention, which has been shown to dramatically improve hygienic water quality in dozens of studies, both open and blinded, some covering follow-up periods of more than five years (4). However, they raise three issues that warrant a response: (i) that the epidemiological evidence in support of HWT may be largely or entirely due to bias, (ii) that commercial solutions and private sector participation should be viewed with suspicion, and (iii) that HWT will divert resources away from the priorities of improving water access and sanitation. Schmidt and Cairncross cite the results from a recent Cochrane review of more than 30 trials of HWT interventions showing the intervention to be protective against diarrheal disease (2). They attach particular significance to the differences in results between the open and blinded trials, citing work by Wood and colleagues for the exaggerated effect of open trial designs with nonobjective outcomes (5). However, Wood and colleagues concluded that these factors collectively inflated the actual effect by about a quarter. Adjusting the pooled effect from the HWT trials by this factor would still yield a protective effect of more than 30%sa very substantial benefit given the heavy burden of diarrheal disease and the comparatively low cost of some HWT interventions. 5542
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Schmidt and Cairncross wrongly suggest that these HWT trials include only subjective health outcomes. Two studies that collected and analyzed stool samples in addition to reported diarrhea found a lower prevalence of diarrheagenic agents among intervention group members and substantial reductions in reported diarrhea (4, 5). In one of the few blinded trials of HWT, anthropometrics showed that intervention group members were less likely to suffer from malnutrition than those in the control group (6), and in perhaps the ultimate objective metric, Crump and colleagues reported fewer deaths among intervention group members using HWT (RR 0.58, P ) 0.036) as well as reductions in reported diarrhea when compared to a control group (7). The only new study cited by Schmidt and Cairncross adds little to the evidence. In an unpublished study, Jain and colleagues (8) randomly allocated chlorine (sodium dichlorisocyanurate) tablets and a tightly covered vessel with a tap to the study population in Ghana and followed them for a period of 12 weeks. Control households received placebo tablets without the chlorine compound but received the same specialized vessel. Because of unforeseen circumstances, the control group had little exposure to waterborne diarrheagenic pathogens in their source water (99% used tap water); moreover, the storage vessels, which were used by the control and intervention groups, minimized recontamination of stored water in the home (median of 16 and 1 CFU of E. coli /100 mL at midterm and end of study, respectively). With little exposure to waterborne pathogens, the investigators were not surprised that the intervention and control groups experienced the same low levels of diarrhea (10). Schmidt and Cairncross cite high levels of heterogeneity in the meta-analysis of open trials as evidence of bias. In fact, such heterogeneity would be expected in view of the clinical and methodological heterogeneity among the studies (11); bias alone without underlying differences would actually increase homogeneity. The differences include exposure (pathogens, transmission pathways, and preventative measures such as hygiene and sanitation), interventions (filters, disinfectants, and hybrids), methods of delivery, levels of compliance, and study methodologies (case definitions of diarrhea, manner of disease surveillance, measures of disease frequency, and measures of effect). The major factor influencing the effect in a specific situation is likely to be the extent to which water is the dominant pathway for transmission of diarrheagenic agents. Thus, any given trial, blinded or open, is unlikely to yield an estimate of effect that is fully generalizable because the underlying effect will depend on transmission dynamics that vary according to settings, seasons, and other factors. The fact that the magnitude of an effect varies is not an argument against scaling up an intervention. Rather it points toward the need to study these influences and learn how to best target the intervention to maximum public health benefit. Schmidt and Cairncross note that studies of HWT interventions in North America and Australia have shown no health benefits. However, the source water in those studies met international quality standards, while those in poor countries where the interventions were reportedly effective do not. Thus, these studies are actually compatible with the other evidence on HWT. They also cite two studies in which HWT interventions were reportedly protective despite low levels of use. As noted above, the effect size is likely to depend on a variety of factors and not simply compliance. The conclusion from all of the studies included in the Cochrane 10.1021/es9008147 CCC: $40.75
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review was that the effect of the intervention was greater among study populations with higher compliance, a conclusion that is consistent with an effective intervention (2). Despite their insistence on more evidence, Schmidt and Cairncross are curiously willing to exclude boiling and safe storage from their criticism. This is true even though boiling is the single HWT for which there are no interventional studies assessing health impact, and safe storage has only a single trial which showed no statistical effectiveness against diarrhea. As actually practiced in hygiene-challenged environments, boiling has not always yielded water that is safe at the point it is actually consumed because of irregular treatment and recontamination during use (12). Safe storage has been shown effective in minimizing the contamination of stored water in the home but unless accompanied by effective HWT is obviously not a solution for the hundreds of millions whose water is unsafe at the point of collection. Schmidt and Cairncross express suspicion about the role of “commercial products” and “industry partners” in HWT, even though they previously opined that “the private sector, which has particular capacity for addressing the needs of householders, should be explored as a potential source for developing effective, low-cost water treatment interventions on a wide scale” (2). Elsewhere, Cairncross also embraced the contribution of the private sector in promoting handwashing (13). While the private sector may not reach the base of the economic pyramid, it has demonstrated its capacity to provide important health interventions such as soap, ORS, and condoms to vulnerable populations. Governments can help ensure these products are safe, effective, and properly targeted. Those of us who undertake research supported by the private sector already register our trials and take special precautions, in addition to those imposed by our institutions, to guard against undue influence. To imply, as Schmidt and Cairncross do, that there is any similarity between commercial enterprises in rich countries that sell bottled water with no “measurable effect on health” and small factories making and selling microbiologically effective products such as chlorine solution in Kenya or ceramic filters in Cambodia is disingenuous and misleading. Underlying much of the concern with promoting HWT expressed by Schmidt and Cairncross appears to be the assumption that funding of water, sanitation, and hygiene is a zero-sum game: that HWT extension would divert resources away from infrastructural interventions. This perspective illustrates the intrasectoral competition that has sometimes characterized the water, sanitation, and hygiene sector and perhaps limits it from sharing in the major surges in funding that have benefitted AIDS, malaria, and other diseases. However, Schmidt and Cairncross acknowledge that there is in fact little evidence of any such diversion and that in any event it may be small. Much of the cost to improve household water supplies, by digging and protecting wells and installing pumps, is borne by the householders themselves. This has also been the case with HWT, whether by boiling or using commercial methods. Schmidt and Cairncross also speculate that governments may use HWT to divert attention from failures in public water supplies. However, increasing householder awareness of deficiencies in water quality at the point of distribution may actually have the opposite effect. Finally, Schmidt and Cairncross repeat the point raised in dozens of previous studies on HWT: that there is a need to demonstrate that the intervention will be used correctly and consistently by vulnerable populations over the longterm. However, these questions cannot be adequately addressed simply by more efficacy studies called for by Schmidt and Cairncross; they can be understood better in
the context of larger-scale effectiveness studies and assessments of actual implementation programs (4). These assessments will yield information on targeting the intervention, improving access, and optimizing uptake, while helping elucidate the determinants of effectiveness in order to provide public health professionals with further evidence for policy making and decision taking. Public health officials can be paralyzed into inaction by the lack of complete evidence. Epidemiologists can aggravate the problem by excessive caution and the need for more studies and more precision. While acknowledging the need for additional research, we believe that effortssby all stakeholderssto promote safe and microbiologically effective HWT should not be delayed while that research continues. Behavior change interventions such as HWT can be more challenging and take longer to achieve adoption than simple improvements in infrastructure, but they can also be a costeffective and enduring way to reach the most vulnerable populations. Drinking water that is free from high levels of fecal contamination is not a sufficient condition to human health, but it is a necessary one that is far from the reach of billions of people worldwide. HWT offers an opportunity to provide the most needy populations with a tool to take charge of improving their own water security, while they patiently wait for the pipe to finally reach them. Disclosure of Interests. The authors include researchers who
have undertaken studies on HWT funded by UN agencies, bilaterals, governments, foundations, NGOs, and private companies, all as disclosed in their respective publications.
Note Added after ASAP Publication Due to a production error, there were some minor text changes in the version of this paper which posted ASAP June 12, 2009; the corrected version published ASAP June 17, 2009.
Literature Cited (1) Schmidt W.; Cairncross, S. Household water treatment in poor populations: Is there enough evidence for scaling up now? Environ. Sci. Technol. 2007, DOI: 10.1021/ es802232w. (2) Clasen, T.; Roberts, I.: Rabie, T.; Schmidt, W.; Cairncross, S. Interventions to improve water quality for preventing diarrhoea. Cochrane Database Syst. Rev. 2006, 3:CD004794. (3) Rosa, G.; Clasen, T. Estimating the scope of household water treatment in middle- and low-income countries. , submitted for publication. (4) Brown, J.; Proum, S.; Sobsey, M. D. Sustained use of a household-scale water filtration device in rural Cambodia. J. Water Health 2009, 7 (3), 404–12. (5) Wood, L.; Egger, M.; Lotte Gluud, L.; Schulz, K. F.; Juni, P.; Altman, D. G.; Gluud, C.; Martin, R. M.; Wood, A. J. G.; Stern, J. A. C. Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes: Meta-epidemiological study. BMJ 2008, 336, 601–605. (6) Mahfouz, A. A.; Abdel-Moneim, M.; al-Erain, R. A.; al-Amari, O. M. Impact of chlorination of water in domestic storage tanks on childhood diarrhoea: A community trial in the rural areas of Saudi Arabia. J. Trop. Med. Hyg. 1995, 98 (2), 126–30. (7) Quick, R. E.; Venczel, L. V.; Mintz, E. D.; Soleto, L.; Aparicio, J.; Gironaz, M.; Hutwagner, L.; Greene, K.; Bopp, C.; Maloney, K.; Chavez, D.; Sobsey, M.; Tauxe, R. V. Diarrhoea prevention in Bolivia through point-of-use water treatment and safe storage: A promising new strategy. Epidemiol. Infect. 1999, 122 (1), 83–90. (8) Austin, C. J. Investigation of In-House Water Chlorination and Its Effectiveness for Rural Areas of the Gambia. Ph.D. Dissertation. Tulane University School of Public Health and Tropical Medicine: New Orleans, LA, 1992. (9) Crump, J. A.; Otieno, P. O.; Slutsker, L.; Keswick, B. H.; Rosen, D. H.; Hoekstra, R. M.; Vulule, J. M.; Luby, S. P. Household VOL. 43, NO. 14, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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based treatment of drinking water with flocculant-disinfectant for preventing diarrhea in areas with turbid source water in rural western Kenya: Cluster randomized controlled trial. BMJ 2005, 331 (7515), 478–484. Jain, S.; Sahanoon, O.; Blanton, E.; Schmitz, A.; Imoro, T.; Hoekstra, M.; Quick, R. The Impact of Sodium Dichlorisocyanurate Treatment on Household Drinking Water Quality and Health in Peri-Urban Ghana: A Randomized Placebo-Controlled, Double-Blinded Trial. International Symposium and 4th Annual Network Meeting, Accra, Ghana, June 2-5, 2008. Thompson, S. G. Why and how sources of heterogeneity should be investigated. In Egger, M., Smith, G. D., Altman, D. G. Eds.; Systematic Reviews in Health Care. BMJ Books: London, 2001. Gupta, S. K.; Suantio, A.; Gray, A.; Widyastuti, E.; Jain, N.; Rolos, R.; Hoekstra, R. M.; Quick, R. Factors associated with E. coli contamination of household drinking water among tsunami and earthquake survivors, Indonesia. Am. J. Trop. Med. Hyg. 2007, 76, 1158–1162. Curtis, V.; Cairncross, S. Water, sanitation, and hygiene at Kyoto. BMJ 2003, 327, 3–4.
Jamie Bartram Gillings School of Global Public Health, University of North Carolina at Chapel Hill
John Colford School of Public Health, University of California-Berkeley
Stephen Luby International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR, B)
Robert Quick Centers for Disease Control and Prevention
Mark Sobsey
Thomas Clasen*
Gillings School of Global Public Health, University of North Carolina at Chapel Hill
London School of Hygiene & Tropical Medicine
ES9008147
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