EBM library: Systematic reviews to support humanitarian medicine

The EBM library signposts some essential reading for the practice of Evidence Based Medicine. In this part of the library we highlight the role of systematic reviews in humanitarian medicine.

Systematic reviews have made significant contributions to the pool of best available evidence in healthcare. In a previous post, we explored the importance of systematic reviews to health care policymakers, and the challenges that come with trying to increase their uptake. In this blog, to mark Humanitarian Evidence week, I provide an example of how systematic reviews can influence humanitarian medicine.

Paper: Clasen, T.F., Alexander, K.T., Sinclair, D., Boisson, S., Peletz, R., Chang, H.H., Majorin, F. and Cairncross, S., 2015. Interventions to improve water quality for preventing diarrhoea. The Cochrane Library.

According to the World Health Organisation (WHO), diarrhoeal disease is the second leading cause of death in low-income countries, with estimates of 57.2 deaths per 100,000 population. In contrast, mortality from diarrhoeal disease is not listed in the top 10 causes of death in high-income countries. One of the main factors for this disparity is the poor water sanitation found in low-income countries, which leads to higher rates of microbiological contamination.

Effective interventions to improve water sanitation, particularly at the point of use, are therefore likely to prevent a considerable number of deaths. In their Cochrane review, Thomas Classen and colleagues evaluated interventions to improve water quality for preventing diarrhoea. They classified these inventions into four categories:

  • Physical removal of pathogens (for example, filtration, adsorption, or sedimentation).
  • Chemical treatment to kill or deactivate pathogens (most commonly with chlorine).
  • Disinfection by heat (for example, boiling or pasteurisation) or ultraviolet (UV) radiation (for example, solar disinfection, or artificial UV lamps).
  • Combination of these approaches (for example, filtration or flocculation combined with disinfection).

The authors identified fifty-five relevant studies, sampled from mostly lower middle or low-income countries and including 84,023 participants.

Six of the included studies (four cluster-RCTs and two quasi-RCTs) evaluated solar water disinfection (SODIS) interventions. This type of disinfection originated in the 1980s and involves the use of UV radiation from sunlight. Essentially, polyethene terephthalate (PET – a sort of recyclable plastic) bottles are first cleaned with soap. The bottles are filled with water, sealed and placed in direct sun exposure, e.g. on top of a low roof, for at least 6 hours. A newspaper is positioned underneath and, if after 6 hours the letters of the headline are readable, the water can be used.


Of the four cluster-RCTs evaluated in the systematic review, there was moderate quality evidence that the use of SODIS treatments reduced the risk of diarrhoea by approximately a third. There are several other advantages to SODIS: simplicity of use and acceptability; low/no cost if using recycled plastic bottles; minimal change in taste of the water and a low risk of recontamination if water is served and stored in small narrow-necked bottles.


Disadvantages of SODIS also need to be considered: the need to pretreat water of higher turbidity; the limited volume of water that can be treated all at once and the need for extensive stocks of PET bottles.  Nevertheless, the impact of the evidence for SODIS use has been considerable. The Centres for Disease Control and Prevention estimates that over 2 million people in 28 developing countries use SODIS for daily drinking water treatment.

Systematic reviews have the potential for far reaching impact. As highlighted above, this extends into humanitarian medicine. If you are interested in this area, the Evidence Aid website contains a collection of assessed published systematic reviews identified as being of relevance to natural disasters, humanitarian crises or major healthcare emergencies.

Kamal R Mahtani is an GP and deputy director of the Centre for Evidence Based Medicine, Nuffield Department of Primary Care Health Sciences, University of Oxford. He is also the director of the the evidence based healthcare MSc in systematic reviews  

You can follow him on Twitter @krmahtani

Disclaimer: The views expressed in this commentary represent the views of the author and not necessarily those of his host institution, the NHS, the NIHR, or the Department of Health.

Acknowledgements: Jeffrey Aronson for helpful discussions. Pictures from Wikipedia (By SODIS Eawag – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=3857398)

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