Treating household drinking water with chlorine tablets does not prevent diarrhoea, study concludes

BMJ 2013; 347 doi: (Published 30 August 2013) Cite this as: BMJ 2013;347:f5372
  1. Cheryl Travasso
  1. 1Mumbai

Using tablets to chlorinate household drinking water does not reduce the prevalence of diarrhoea in children, a study conducted in India has found.

Diarrhoeal diseases affect over 287 000 people each year in India. Some research has indicated that household water treatment and safe storage interventions, such as boiling, chlorinating, and filtering, can reduce the incidence of diarrhoea by 30-40%. As a result the World Health Organization and Unicef have recommended such an approach, particularly in populations that do not have access to safe water supplies. In India only 11% of people in rural areas have a household water supply.

However, a large double blind randomised trial conducted by researchers in India and the London School of Hygiene and Tropical Medicine has found that use of chlorine tablets by households in Odisha state had no effect on the prevalence of diarrhoea among children aged under 5 living in those households.

The study, published in PloS Medicine, included 2163 households and 2986 children under 5 in rural and urban communities in Odisha: 11 informal settlements in Bhubaneswar and 20 villages in the state. The households were randomised to receive either sodium dichloroisocyanurate disinfection tablets or placebo tablets.1

Over the 12 months of follow-up the proportion of children with diarrhoea was 1.69% in the households that received chlorine tablets and 1.74% in the control households. After adjusting for clustering of cases of diarrhoea, the researchers found that the prevalence ratio for diarrhoea in the intervention compared with the control group was 0.95 (95% confidence interval 0.79 to 1.13).

But the researchers found that many households did not use the tablets properly. Although 51% of households in the intervention group reported that they treated their water with the tablets, only 32% of water samples in these households tested positive for chlorine. Overall, 20% of the 1080 intervention households never had residual chlorine in their child’s water during follow-up visits, and 76% had chlorine on less than half of the visits.

The lead researcher, the London School of Hygiene and Tropical Medicine’s Thomas Clasen, told the BMJ that he “would not want to speculate on whether the lack of protective effect is due here to poor compliance or something else.”

The study population was exposed to several routes of transmission for faecal bacteria and viruses, and although chlorine is effective against faecal bacteria and viruses in drinking water, improvement in water quality alone would not be enough to prevent diarrhoea in settings with several sources of exposure to faecal pathogens. Sanitation coverage and frequency of handwashing with soap were low in the study population, indicating that other transmission routes may have had an important role, Clasen said.

Tackling all transmission routes would be expensive, he added, so it was important to look for simple measures, such as treating drinking water, particularly in communities where water sources were likely to be contaminated. Despite the study’s findings, Clasen said that household water treatment and safe storage interventions were an essential and “effective, acceptable, affordable, accessible, and sustainable option that can be implemented on a wide scale.”


Cite this as: BMJ 2013;347:f5372


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