Health Stream Literature Summary - Issue 56 - December 2009

Solar drinking water disinfection (SODIS) to reduce childhood diarrhoea in rural Bolivia: A cluster-randomized, controlled trial
Mausezahl, D., Christen, A., Pacheco, G.D., Tellez, F.A., Iriarte, M., Zapata, M.E., Cevallos, M., Hattendorf, J., Cattaneo, M.D., Arnold, B., Smith, T.A. and Colford Jr, J.M. (2009) PLoS Medicine, 6(8); e1000125

Worldwide, 1.8 million people die every year from diarrhoeal diseases with the majority being children under the age of 5 years living in developing countries. The most important global risk factors for diarrhoeal illness are considered to be unsafe water, sanitation and hygiene. Solar drinking water disinfection (SODIS) is a widely promoted low-cost, point-of-use water disinfection method that has been disseminated globally. In the laboratory setting SODIS is highly efficacious in inactivating waterborne pathogens. However evidence of the effectiveness of SODIS from field studies is limited. A community-randomised intervention trial was conducted to evaluate the effectiveness of SODIS in decreasing diarrhoea in children under 5 years in rural communities in Bolivia.

This trial, the Bolivia Water Evaluation Trial (Bolivia WET), was conducted in Quechua in rural Totora District, Cochabamba Department, Bolivia. This study was part of a comprehensive SODIS roll-out program. Most of the local residents were farmers living in small compounds of three building with mud floors, with five or more persons sleeping in the same room. There were 15% of homes which had a latrine or other sanitary facilities and most residents defecated in the nearby environment. Drinking water was normally stored in 10-l plastic buckets or open jerry cans of 5-20 l in the household. Baseline assessments of the drinking water quality in the home indicated a median contamination of thermotolerant coliforms (TTC) of 32 TTC/100ml. Giardia lamblia and Cryptosporidium parvum were detected in 18/24 and 11/23 community source water samples, respectively.

There were 11 communities (262 households and 441 children) that were randomised to the SODIS intervention and 11 communities (222 households and 378 children) served as a control group. For 15 months an intensive, standardised and repeated interactive promotion of the SODIS method was implemented in the intervention communities beginning 3 months before the start of follow-up. Those participating households in the intervention arm were supplied regularly with clean, recycled PET bottles. The households were taught to expose the water-filled bottles for at least 6 hours to the sun. The importance and benefits of drinking only treated water (especially for children) was emphasized, the germ-disease concept was explained and hygiene measures such as safe drinking water storage and hand washing were promoted.

The primary outcome was the incidence rate of diarrhoea among children under 5 years and this was measured by community-based field workers. Mothers or closest caretakers kept a 7-day morbidity diary recording daily any occurrence of diarrhoea, fever, cough and eye irritations in study participants. Community-based field workers visited households weekly to collect the health diaries. Child exposure risks were assessed by community-based staff interviewing mothers once during baseline and twice during the 1 year follow-up. Compliance with the SODIS method was assessed using four different subjective and objective indicators.

Data were obtained from 376 children (225 households) in the intervention arm and 349 children (200 households) in the control arm. Information was collected on the occurrence of diarrhoea for 166,971 person-days representing 79.9% and 78.9% of the total possible person-days of child observation in the intervention and control arms. Follow-up began in June 2005 and ended in June 2006. At baseline the main types of water sources for household chores and drinking were similar in both study arms, as was the distance to the source. Nearly 30% of all households reported treating water regularly before drinking, with boiling water the most common treatment before the trial (20.2% in both arms). Children in the SODIS-intervention had a total of 808 episodes of diarrhoeal illness or a mean of 3.6 per child per year-at-risk. In the control arm there were 887 episodes and an annual mean of 4.3 per child per year. The median length of diarrhoea episodes in both arms was 3 days. The unadjusted relative rate (RR) estimate (0.81, 95% CI 0.59-1.12) suggested no statistically significant difference in the number of diarrhoea episodes between the SODIS and control study arms. No significant treatment effect (odds ration [OR] =0.92, 95% CI 0.66-1.29) was found in an analysis of the longitudinal prevalence of diarrhoea. No strong evidence was found for the reduction of odds of severe diarrhoea cases (OR =0.91, 95% CI 0.51-1.63) and dysentery (OR =0.80, 95% CI 0.55-1.17). A multivariable model adjusting for age, sex, baseline-existing water treatment practises and child hand washing was consistent in its estimate of effect (RR = 0.74, 95% CI 0.50-1.11). There was no evidence that increased compliance was associated with a lower incidence of diarrhoea in the intervention arm. The incidence of diarrhoeal illness did not decline with increased weeks of using SODIS.

There was no strong evidence for a substantial reduction in incidence rate of diarrhoea among children in this study despite a comprehensive and intensive intervention promotion campaign. It is suggested that before further global promotion of SODIS, a clearer understanding is required of: the discrepancy between laboratory and field results, the role of compliance in effectiveness of SODIS, and a direct comparison is made of SODIS to alternative drinking water treatment methods.

Comment This paper includes some informative discussion of ethical and political issues surrounding the conduct of community-based research studies, as well as practical aspects of assessing compliance with study protocols in this context.

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