3 Discussion 3.3 Impact on policy and practice of the presented research PAFs and related risk factor-attributable burden of disease estimates quantify the importance of a risk factor on human health. They provide a bridge between the risk factor-disease association as usually derived in epidemiological studies and the prevalence of the risk factor in a given population (23). Even when relative risks are large the public health relevance of a risk factor might be small when only a small fraction of the population is exposed (23,111). The public health relevance might be large when there is substantial exposure with a risk factor with a small relative risk (23,111). The PAF can be interpreted as the proportion of disease cases or deaths that could have potentially been prevented given effective interventions to remove or reduce the risk factor were available. Results of burden of disease assessments are therefore relevant to policy-making, can guide the choice of the most urgent interventions and are easy to understand and to communicate (23,25,111). Environmental disease burden estimates are important for raising awareness about the importance of environmental factors for health. Probably the most prominent example of the presented work is the comprehensive burden of disease assessment attributable to environmental risks (section 2.6 (3,9)). Results of this assessment were reported in over 170 newswires and newspapers in English, French and Spanish and in numerous other languages throughout the world (examples include (118–122)) and were also extensively communicated via social media (examples include (123,124)) and in a radio interview (125). Following the publication of the WHO WASH-attributable burden of disease estimates for the year 2012 (section 2.5 (40)), the subsequent Global Burden of Disease study for the year 2013 changed its approach of estimating WASH-attributable disease burden (38). By using counterfactual exposure distributions that extended from improved drinking water and sanitation facilities to higher levels of WASH service provision including hygiene, estimated WASH-attributable disease burden increased by a factor of four between the Global Burden of Disease studies 2010 and 2013 (18,38). The IHME Global Burden of Disease study estimated 337,000 deaths from inadequate WASH in 2010 (18), which changed to 1,399,000 deaths in 2013 (38), 1,766,000 deaths in 2015 (39), 1,661,000 deaths in 2016 (37) and 1,610,000 in 2017 (24) (estimates for 2016 and 2017 include deaths from lower respiratory infections attributable to inadequate hygiene, Table 1). The Global Burden of Disease assessment for the year 2016 attributed 89% of global diarrhoea deaths to inadequate WASH (37) while the WHO assessment for the year 2016 attributed 60% of global diarrhoea deaths to inadequate WASH (section 2.12 (12)). Table 1: WHO and GBD WASH-attributable disease burden estimates over time Year of estimates WASH-attributable diarrhoeal deaths (thousands) Hygiene-attributable deaths from lower respiratory infections (thousands) WHO GBD (IHME) WHO GBD (IHME) 2010 - 337 - - 2012 842 - - - 2013 - 1,399 - - 2015 - 1,766* - - 2016 829 1,481 370 179 2017 - 1,422 - 188 * Includes diarrhoeal diseases, typhoid and paratyphoid fever; WASH: water, sanitation and hygiene, WHO: World Health Organization, GBD: Global Burden of Disease, IHME: Institute for Health Metrics and Evaluation Reasons for the differences between the WHO estimates and those from the Global Burden of Disease study from the year 2013 onwards include different counterfactuals or minimum risk exposure levels and the adjustment for likely bias due to lack of blinding in the WHO assessments. In the Global Burden of Disease studies the minimum risk exposure levels were defined as high-quality drinking water that is filtered or boiled at point-of-use, sanitation connected to sewer or septic tank and access to handwashing stations with soap and water (24,37–39). In the WHO assessments, the minimum risk exposure level for drinking water was defined as water from any source that is filtered or boiled at household level (12,40). This choice was based on the scarcity of data for the exposure-response relationship between higher-quality piped water and disease (41,52). The current minimum risk exposure level for the WHO sanitation assessment is high, i.e., above 75% of the population, community coverage with basic sanitation facilities (12). For the hygiene assessment, the WHO uses the proportion of the population with access to handwashing facilities with soap and water but subsequently adjusts these estimates for actual handwashing with soap (47). Transparency of methods and estimates seems especially important in light of such differing estimates. However, the earlier systematic review conducted by the IHME is only available as an abstract (36). The updated systematic review is only mentioned in the appendix of the comparative risk assessment for the Global Burden of Disease study 2017 and is described as an update of the here presented systematic review (section 2.3 (41))(56). In contrast, the search strategies, the included studies, the extracted variables, and the input as well as the results data at disaggregated level from the here presented systematic reviews, meta-analyses and WASH-attributable burden of disease assessments have been made available allowing re-calculation and data usage. The WHO is reporting on several WASH-related SDG indicators, including the proportion of the population using safely managed sanitation services (Indicator 6.2.1), the proportion of wastewater safely treated (Indicator 6.3.1), and the mortality from unsafe water, sanitation and hygiene (Indicator 3.9.2) (94). The here presented WHO burden of disease estimates (sections 2.5 and 2.12) provided the data basis for the annual monitoring of the SDG target indicator 3.9.2 on WASH-attributable mortality (126). The methods for risk factor-attributable burden of disease assessment that are described in this critical analysis have been used for an analysis of the potential impacts on health of the Indian Swachh Bharat Mission (SBM, Clean India Mission) which is a nation-wide campaign to end open defecation (127,128). Following the start of the SBM in 2014 and documented by household surveys, open defecation in rural India declined by about 12 percentage points per year between 2015 and 2019 compared to only 3 percentage points decline between 2000 and 2014 (6). The analysis which was conducted by the WHO with my contributions, estimated that the SBM could avert about 300,000 deaths from diarrhoea and protein-energy malnutrition provided the mission’s goal of all the Indian population using safe sanitation by October 2019 was achieved (129). These results were quoted by the Indian Prime Minister in 2018 in his yearly speech on Independence Day and were also reported by the Indian media (130–132). The knowledge and skills I acquired while conducting the research presented in this critical analysis enabled me to participate in discussions about environmental burden of disease assessments for example in Germany. Environmental health research is frequently subject to scientific misinformation that aims to influence public perceptions, reduce trust in research and impedes evidence-based policy making (133). Similarly, environmental disease burden assessments have been challenged regarding their validity and verity. One example is a recent debate in Germany about the disease burden attributable to NO2 emissions (134,135). I contributed to frequently asked questions around environmental burden of disease assessments that were published on the WHO website and I am co-authoring a letter to the editor rebutting the criticism which was largely around calculating the PAF and the methods applied for calculating risk factor-attributable burden of disease estimates (136,137). 4 Concluding issues in WASH- and risk factor-attributable disease In document Estimating burden of disease due to environmental factors with an emphasis on inadequate water, sanitation and hygiene (Page 61-65)
