Estimates on the WASH-related Global Burden of Disease

Below are abstracts and links to the full-text of articles in the August 2014 issue of  Tropical Medicine and International Healthtmih

Focus on the Global Burden of Disease from Water
While the methods of Global Burden of Disease (GBD) study continue to evolve, recent changes raise questions about the basis of new estimates of the risk associated with water, sanitation and hygiene and warrant consideration of alternative approaches.

  • ​Inadequate water, sanitation and hygiene are estimated to have caused 842,000 deaths from diarrhoea in 2012, i.e., 1.5% of deaths worldwide. These include 361,000 deaths of children under five years.
  • ​A systematic review of the global prevalence of handwashing with soap and its effect on diarrhoeal diseases estimates that only 19% of the world’s population washes hands with soap after contact with excreta and that handwashing reduces the risk of diarrhoeal disease by 23%–40%.
  • ​Based on over 300 studies from a systematic review, an estimated 1.1 billion people are exposed to a drinking water source of moderate to high risk.
  • ​A meta-regression shows that risks of diarrhoea from inadequate drinking water and sanitation could be reduced considerably through targeted interventions. Risk differences depend on type of intervention.

1 – Authors:  Clasen, Thomas, Pruss-Ustun, Annette, Mathers, Colin D., et al.

TI  - Estimating the impact of unsafe water, sanitation and hygiene on the global burden of disease: evolving and alternative methods
Abstract - http://onlinelibrary.wiley.com/doi/10.1111/tmi.12330/abstract
AB  - The 2010 global burden of disease (GBD) study represents the latest effort to estimate the global burden of disease and injuries and the associated risk factors. Like previous GBD studies, this latest iteration reflects a continuing evolution in methods, scope and evidence base. Since the first GBD Study in 1990, the burden of diarrhoeal disease and the burden attributable to inadequate water and sanitation have fallen dramatically. While this is consistent with trends in communicable disease and child mortality, the change in attributable risk is also due to new interpretations of the epidemiological evidence from studies of interventions to improve water quality. To provide context for a series of companion papers proposing alternative assumptions and methods concerning the disease burden and risks from inadequate water, sanitation and hygiene, we summarise evolving methods over previous GBD studies. We also describe an alternative approach using population intervention modelling. We conclude by emphasising the important role of GBD studies and the need to ensure that policy on interventions such as water and sanitation be grounded on methods that are transparent, peer-reviewed and widely accepted.

2 – Authors: Prüss-Ustün, Annette, Bartram, Jamie, Clasen, Thomas,  et al.

TI  - Burden of disease from inadequate water, sanitation and hygiene in low- and middle-income settings: a retrospective analysis of data from 145 countries

Objective - To estimate the burden of diarrhoeal diseases from exposure to inadequate water, sanitation and hand hygiene in low- and middle-income settings and provide an overview of the impact on other diseases.

Methods - For estimating the impact of water, sanitation and hygiene on diarrhoea, we selected exposure levels with both sufficient global exposure data and a matching exposure-risk relationship. Global exposure data were estimated for the year 2012, and risk estimates were taken from the most recent systematic analyses. We estimated attributable deaths and disability-adjusted life years (DALYs) by country, age and sex for inadequate water, sanitation and hand hygiene separately, and as a cluster of risk factors. Uncertainty estimates were computed on the basis of uncertainty surrounding exposure estimates and relative risks.

Results - In 2012, 502 000 diarrhoea deaths were estimated to be caused by inadequate drinking water and 280 000 deaths by inadequate sanitation. The most likely estimate of disease burden from inadequate hand hygiene amounts to 297 000 deaths. In total, 842 000 diarrhoea deaths are estimated to be caused by this cluster of risk factors, which amounts to 1.5% of the total disease burden and 58% of diarrhoeal diseases. In children under 5 years old, 361 000 deaths could be prevented, representing 5.5% of deaths in that age group.
Conclusions - This estimate confirms the importance of improving water and sanitation in low- and middle-income settings for the prevention of diarrhoeal disease burden. It also underscores the need for better data on exposure and risk reductions that can be achieved with provision of reliable piped water, community sewage with treatment and hand hygiene.

3 – Authors: Freeman, Matthew C., Stocks, Meredith E., Cumming, Oliver,  et al.
TI  - Systematic review: Hygiene and health: systematic review of handwashing practices worldwide and update of health effects

Full text: http://onlinelibrary.wiley.com/doi/10.1111/tmi.12339/pdf

Objective - To estimate the global prevalence of handwashing with soap and derive a pooled estimate of the effect of hygiene on diarrhoeal diseases, based on a systematic search of the literature.

Methods - Studies with data on observed rates of handwashing with soap published between 1990 and August 2013 were identified from a systematic search of PubMed, Embase and ISI Web of Knowledge. A separate search was conducted for studies on the effect of hygiene on diarrhoeal disease that included randomised controlled trials, quasi-randomised trials with control group, observational studies using matching techniques and observational studies with a control group where the intervention was well defined. The search used Cochrane Library, Global Health, BIOSIS, PubMed, and Embase databases supplemented with reference lists from previously published systematic reviews to identify studies published between 1970 and August 2013. Results were combined using multilevel modelling for handwashing prevalence and meta-regression for risk estimates.

Results - From the 42 studies reporting handwashing prevalence we estimate that approximately 19% of the world population washes hands with soap after contact with excreta (i.e. use of a sanitation facility or contact with children’s excreta). Meta-regression of risk estimates suggests that handwashing reduces the risk of diarrhoeal disease by 40% (risk ratio 0.60, 95% CI 0.53–0.68); however, when we included an adjustment for unblinded studies, the effect estimate was reduced to 23% (risk ratio 0.77, 95% CI 0.32–1.86).

Conclusions- Our results show that handwashing after contact with excreta is poorly practiced globally, despite the likely positive health benefits.

4 – Authors: Bain, Robert, Cronk, Ryan, Hossain, Rifat,  et al.

TI  - Global assessment of exposure to faecal contamination through drinking water based on a systematic review

Full text: http://onlinelibrary.wiley.com/doi/10.1111/tmi.12334/pdf

Objectives - To estimate exposure to faecal contamination through drinking water as indicated by levels of Escherichia coli (E. coli) or thermotolerant coliform (TTC) in water sources.

Methods - We estimated coverage of different types of drinking water source based on household surveys and censuses using multilevel modelling. Coverage data were combined with water quality studies that assessed E. coli or TTC including those identified by a systematic review (n = 345). Predictive models for the presence and level of contamination of drinking water sources were developed using random effects logistic regression and selected covariates. We assessed sensitivity of estimated exposure to study quality, indicator bacteria and separately considered nationally randomised surveys.

Results - We estimate that 1.8 billion people globally use a source of drinking water which suffers from faecal contamination, of these 1.1 billion drink water that is of at least ‘moderate’ risk (>10 E. coli or TTC per 100 ml). Data from nationally randomised studies suggest that 10% of improved sources may be ‘high’ risk, containing at least 100 E. coli or TTC per 100 ml. Drinking water is found to be more often contaminated in rural areas (41%, CI: 31%–51%) than in urban areas (12%, CI: 8–18%), and contamination is most prevalent in Africa (53%, CI: 42%–63%) and South-East Asia (35%, CI: 24%–45%). Estimates were not sensitive to the exclusion of low quality studies or restriction to studies reporting E. coli.

Conclusions - Microbial contamination is widespread and affects all water source types, including piped supplies. Global burden of disease estimates may have substantially understated the disease burden associated with inadequate water services.

5 – Authors: Wolf, Jennyfer, Prüss-Ustün, Annette, Cumming, Oliver, et al.

TI  - Systematic review: Assessing the impact of drinking water and sanitation on diarrhoeal disease in low- and middle-income settings: systematic review and meta-regression

Full text: http://onlinelibrary.wiley.com/doi/10.1111/tmi.12331/pdf

Objective - To assess the impact of inadequate water and sanitation on diarrhoeal disease in low- and middle-income settings.

Methods - The search strategy used Cochrane Library, MEDLINE & PubMed, Global Health, Embase and BIOSIS supplemented by screening of reference lists from previously published systematic reviews, to identify studies reporting on interventions examining the effect of drinking water and sanitation improvements in low- and middle-income settings published between 1970 and May 2013. Studies including randomised controlled trials, quasi-randomised trials with control group, observational studies using matching techniques and observational studies with a control group where the intervention was well defined were eligible. Risk of bias was assessed using a modified Ottawa–Newcastle scale. Study results were combined using meta-analysis and meta-regression to derive overall and intervention-specific risk estimates.

Results - Of 6819 records identified for drinking water, 61 studies met the inclusion criteria, and of 12 515 records identified for sanitation, 11 studies were included. Overall, improvements in drinking water and sanitation were associated with decreased risks of diarrhoea. Specific improvements, such as the use of water filters, provision of high-quality piped water and sewer connections, were associated with greater reductions in diarrhoea compared with other interventions.

Conclusions - The results show that inadequate water and sanitation are associated with considerable risks of diarrhoeal disease and that there are notable differences in illness reduction according to the type of improved water and sanitation implemented.

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