Sophie Boisson and colleagues conducted a double-blind, randomized placebo-controlled trial in Orissa, a state in southeast India, to evaluate the effect of household water treatment in preventing diarrheal illnesses in children aged under five years of age.
Please see later in the article for the Editors' Summary
Boiling, disinfecting, and filtering water within the home can improve the microbiological quality of drinking water among the hundreds of millions of people who rely on unsafe water supplies. However, the impact of these interventions on diarrhoea is unclear. Most studies using open trial designs have reported a protective effect on diarrhoea while blinded studies of household water treatment in low-income settings have found no such effect. However, none of those studies were powered to detect an impact among children under five and participants were followed-up over short periods of time. The aim of this study was to measure the effect of in-home water disinfection on diarrhoea among children under five.
Methods and Findings
We conducted a double-blind randomised controlled trial between November 2010 and December 2011. The study included 2,163 households and 2,986 children under five in rural and urban communities of Orissa, India. The intervention consisted of an intensive promotion campaign and free distribution of sodium dichloroisocyanurate (NaDCC) tablets during bi-monthly households visits. An independent evaluation team visited households monthly for one year to collect health data and water samples. The primary outcome was the longitudinal prevalence of diarrhoea (3-day point prevalence) among children aged under five. Weight-for-age was also measured at each visit to assess its potential as a proxy marker for diarrhoea. Adherence was monitored each month through caregiver's reports and the presence of residual free chlorine in the child's drinking water at the time of visit. On 20% of the total household visits, children's drinking water was assayed for thermotolerant coliforms (TTC), an indicator of faecal contamination. The primary analysis was on an intention-to-treat basis. Binomial regression with a log link function and robust standard errors was used to compare prevalence of diarrhoea between arms. We used generalised estimating equations to account for clustering at the household level. The impact of the intervention on weight-for-age z scores (WAZ) was analysed using random effect linear regression.
Over the follow-up period, 84,391 child-days of observations were recorded, representing 88% of total possible child-days of observation. The longitudinal prevalence of diarrhoea among intervention children was 1.69% compared to 1.74% among controls. After adjusting for clustering within household, the prevalence ratio of the intervention to control was 0.95 (95% CI 0.79–1.13). The mean WAZ was similar among children of the intervention and control groups (−1.586 versus −1.589, respectively). Among intervention households, 51% reported their child's drinking water to be treated with the tablets at the time of visit, though only 32% of water samples tested positive for residual chlorine. Faecal contamination of drinking water was lower among intervention households than controls (geometric mean TTC count of 50 [95% CI 44–57] per 100 ml compared to 122 [95% CI 107–139] per 100 ml among controls [p<0.001] [n = 4,546]).
Our study was designed to overcome the shortcomings of previous double-blinded trials of household water treatment in low-income settings. The sample size was larger, the follow-up period longer, both urban and rural populations were included, and adherence and water quality were monitored extensively over time. These results provide no evidence that the intervention was protective against diarrhoea. Low compliance and modest reduction in water contamination may have contributed to the lack of effect. However, our findings are consistent with other blinded studies of similar interventions and raise additional questions about the actual health impact of household water treatment under these conditions.
Please see later in the article for the Editors' Summary
Millennium Development Goal 7 calls for halving the proportion of the global population without sustainable access to safe drinking water between 1990 and 2015. Although this target was met in 2010, according to latest figures, 768 million people world-wide still rely on unimproved drinking water sources. Access to clean drinking water is integral to good health and a key strategy in reducing diarrhoeal illness: Currently, 1.3 million children aged less than five years die of diarrhoeal illnesses every year with a sixth of such deaths occurring in one country—India. Although India has recently made substantial progress in improving water supplies throughout the country, currently almost 90% of the rural population does not have a water connection to their house and drinking water supplies throughout the country are extensively contaminated with human waste. A strategy internationally referred to as Household Water Treatment and Safe Storage (HWTS), which involves people boiling, chlorinating, and filtering water at home, has been recommended by the World Health Organization and UNICEF to improve water quality at the point of delivery.
Why Was This Study Done?
The WHO and UNICEF strategy to promote HWTS is based on previous studies from low-income settings that found that such interventions could reduce diarrhoeal illnesses by between 30%–40%. However, these studies had several limitations including reporting bias, short follow up periods, and small sample sizes; and importantly, in blinded studies (in which both the study participants and researchers are unaware of which participants are receiving the intervention or the control) have found no evidence that HWTS is protective against diarrhoeal illnesses. So the researchers conducted a blinded study (a double-blind, randomized placebo-controlled trial) in Orissa, a state in southeast India, to address those shortcomings and evaluate the effect of household water treatment in preventing diarrhoeal illnesses in children under five years of age.
What Did the Researchers Do and Find?
The researchers conducted their study in 11 informal settlements (where the inhabitants do not benefit from public water or sewers) in the state's capital city and also in 20 rural villages. 2,163 households were randomized to receive the intervention—the promotion and free distribution of sodium dichloroisocyanurate (chlorine) disinfection tablets with instruction on how to use them—or placebo tablets that were similar in appearance and had the same effervescent base as the chlorine tablets. Trained field workers visited households every month for 12 months (between December 2010 and December 2011) to record whether any child had experienced diarrhoea in the previous three days (as reported by the primary care giver). The researchers tested compliance with the intervention by asking participants if they had treated the water and also by testing for chlorine in the water.
Using these methods, the researchers found that over the 12-month follow-up period, the longitudinal prevalence of diarrhoea among children in the intervention group was 1.69% compared to 1.74% in the control group, a non-significant finding (a finding that could have happened by chance). There was also no difference in diarrhoea prevalence among other household members in the two groups and no difference in weight for age z scores (a measurement of growth) between children in the two groups. The researchers also found that although just over half (51%) of households in the intervention group reported treating their water, on testing, only 32% of water samples tested positive for chlorine. Finally, the researchers found that water quality (as measured by thermotolerant coliforms, TTCs) was better in the intervention group than the control group.
What Do These Findings Mean?
These findings suggest that treating water with chlorine tablets has no effect in reducing the prevalence of diarrhoea in both children aged under five years and in other household members in Orissa, India. However, poor compliance was a major issue with only a third of households in the intervention group confirmed as treating their water with chlorine tablets. Furthermore, these findings are limited in that the prevalence of diarrhoea was lower than expected, which may have also reduced the power of detecting a potential effect of the intervention. Nevertheless, this study raises questions about the health impact of household water treatment and highlights the key challenge of poor compliance with public health interventions.
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001497.
The website of the World Health Organization has a section dedicated to household water treatment and safe storage, including a network to promote the use of HWTS and a toolkit to measure HWTS
The Water Institute hosts the communications portal for the International Network on Household Water Treatment and Safe Storage