ENVIRONMENTAL BURDEN OF DISEASE

Definition of disease burden

Disease burden is the impact of a health problem in an area measured by financial cost, mortality, morbidity, or other indicators. It is often quantified in terms of quality-adjusted life years (QALYs) or disability-adjusted life years (DALYs), which combine the burden due to both death and morbidity into one index. One DALY can be thought of as one lost year of healthy life ,and the burden of disease can be thought of as a measure of the gap between current health status and an ideal situation where the individual lives into old age free from disease and disability. (1, 2, 3)

Definition of environmental burden of disease
The environmental burden of disease is the number of DALYs that can be attributed to environmental factors. (4, 5, 3)

History
The First global burden disease (GBD) study (in 1990) quantified the health effects of more than 100 diseases and injuries for eight regions of the world. It generated comprehensive and internally consistent estimates of morbidity and mortality by age, sex and region. It also introduced a new metric – the Disability-Adjusted Life Year (DALY) – to quantify the burden of diseases, injuries and risk factors. The DALY is based on years of life lost from premature death and years of life lived in less than full health. (3,6,7)

Murray and Lopez used DALYs in their extensive Global Burden of Disease study to introduce morbidity into the predominantly mortality-based health discussions. Then the World Health Organization (WHO) endorsed the DALY approach which used in various studies on global, national and regional levels. In the year 2000-2002 the (GBD 1990 study) was updated and included a more extensive analysis of the mortality and burden of disease attributable to 26 global risk factors using a consistent analytic framework known as Comparative Risk Factor Assessment (CRA). Then updated in the year 2004. (6)

In 2005 a comparison of 17 EBD (environmental burden of disease) studies published between 1996 and 2005, revealing significant differences between EBD estimate that concern – at first sight – similar issues. For example Smith et al. estimate the fraction of the total global disease burden attributable to the environment to be 25–33%, whereas Melse and de Hollander estimate this to be 7.5 to 11% (for OECD countries only: 2–5%). These differences are not be fully explained by reading the assessment reports. (6)

The "Modifiable" Environment; and Environmental Risk Factors

In 2006, WHO released a "Preventing disease through healthy environments: towards an estimate of the global burden of disease" report, about how much of global disease could be prevented by modifying the environment. It was based on the World Health Report 2002 and involved a systematic review of literature as well as surveys of over 100 experts worldwide. (4)

The report confirmed that approximately one-quarter of the global disease burden, and more than one-third of the burden among children, is due to modifiable environmental factors. This 'environmentally-mediated' disease burden is much higher in developing countries than in developed countries. However certain non-communicable diseases, such as cardiovascular diseases and cancers, the per capita disease burden is larger in developed countries. Children bear the highest death toll with more than 4 million environmentally-caused deaths yearly, mostly in developing countries. The infant death rate attributed to environmental causes is 12 times higher in developing than in developed countries, reflecting the human health gain that could be achieved by supporting healthy environments. Moreover, the report gave the fraction of disease that can be attributed to the environment and that could be prevented, for 85 out of the 102 major diseases and injuries classified by WHO. (4)

To measure the environmental health impact, environment was defined as: "Environment is all the physical, chemical and biological factors external to a person, and all the related behaviours". This definition excludes behaviour not related to environment, as well as behaviour related to the social and cultural environment, and genetics. This limited environment to the modifiable environment in which those parts of the environment that can be modified by short-term or longer-term interventions, so as to reduce the health impact of the environment. (8)

So, based on the definition of modifiable environment above, it includes:

Air, soil & water pollution with chemicals or biological agents
Ultraviolet and ionizing radiation
Noise, electromagnetic fields
Built environment
Agricultural methods, irrigation schemes
Anthropogenic climate changes, ecosystem degradation
Occupational risks
Individual behaviors related to the environment, such as hand-washing, food contamination with unsafe water or dirty hands. (8,9)

Whereas environmental risk factors that are considered in quantifying the disease burden, include:

Indoor smoke from solid fuel use
Outdoor air pollution
Second-hand smoke
Water, sanitation & hygiene
Solar ultraviolet radiation
Climate change
Occupational carcinogen
Occupational airborne particulates
Lead
Mercury. (10)

Methodology Of Estimating The Burden Of Disease

WHO developed a methodology to quantify the health state of a population and to evaluate the global burden of disease in order to determine strategic planning and set priority actions in public health. Summary measures of population health (SMPH) were developed, that combine information on mortality and non-fatal health outcomes. The SMPH can be divided into two distinct categories: the health gap measures and the health expectancies. The most commonly used is the Disability-adjusted life year, DALY (2, 7, 9). This metric measure permits the comparison of the burden due to various environmental risk factors with other risk factors or diseases. (9)

Additional information required for the rational development of policies by the health sector and activities of other sectors that manage directly or influence the determinants of health which includes:

the effectiveness and cost-effectiveness of interventions
the type of policy environment
the availability of resources. (13)

The exposure-based approach (When exposure is measured in terms of increasing levels of pollutants, the approach called exposure-based ) used to calculate the environmental burden of disease, supported by a comprehensive analysis of the evidence for the given health risks. It can be used to assess broad, large scale and non-specific environmental health relationships. (14)

Exposure-based approach needs the following data:

Identification of outcomes associated with the relevant risk factor
Assessment of exposure in the study population
The exposure distribution of the study population needs to be estimated on the basis of measured data.
Dose-response relationships based on a ‘sufficient level of evidence’.

A dose-response relationship as a function of the exposure parameter assessed for the study population needs to be defined (2). Exposure distribution and dose-response relationships are then combined to yield health impact distributions in the study population. Health impact distributions, usually expressed in terms of incidence, can then be converted into health summary measures, such as DALYs. Exposure-response relationships for a given risk factor are commonly obtained from epidemiological studies, and the derived attributable fractions are then applied to disease burden, expressed in deaths or DALYs, associated with the risk factor (2, 3). For example, the disease burden of outdoor air pollution for Santiago, Chile, was calculated by measuring the concentration of particulate matter (PM10) in the air, estimating the susceptible population, and combining these data with relevant dose-response relationships. A reduction of particulate matter levels in the air, to recommended standards would cause a reduction of about 5’200 deaths, 4’700 respiratory hospital admissions, and 13’500’000 restricted activity days per year, for a total population of 4.7 million. (2)

In 2002, WHO estimated the environmental burden of disease globally by using a combination of comparative risk assessment data and expert judgment to develop environmentally attributable fractions (EAFs) of mortality and morbidity for 85 categories of disease.(2, 3, 15)

And in 2007, WHO released the first ever country-by-country analysis of the impact environmental factors have on health for its 192 Member states. These country estimates were the first step to assist national decision-makers in the sectors of health and environment to set priorities for preventive action. It is divided in three parts:

1. Environmental burden of disease attributable to three selected risk factors

It presents the yearly burden, expressed in deaths and DALYs, attributable to the three following risk factors:

Indoor air pollution from solid fuel use
Outdoor air pollution
Unsafe water, sanitation & hygiene

These results are calculated in accordance with the exposure-based approach, in which exposure data that were available globally (indicators such as access to improved water sources, annual mean of particulate matter [PM10], etc.).

2. Preliminary estimates of the total environmental burden of disease for the country

Total number of deaths and DALYs per capita and percentage of the national burden of disease attributable to the environment, represent the disease burden that could be avoided by modifying the environment as a whole.

3. Environmental burden by disease category

Country profile is breakdown by disease group of the information given in part 2. It shows the yearly number of DALYs per capita attributable to environmental factors by disease group. The country rate gives the number of DALYs per capita, indicating the most diseases affected by environmental factors in the country, allowing comparison among the same country and between countries, and allowing a quick overview of which disease is predominantly affected by the environment in the country of interest compared with other countries. (3)

Summary Of Assessing Of Burden Of Disease At National And Local Levels

1: Define parameters of interest

2: Set the framework -
Select the study population of interest; define which geographical boundaries and age groups.

3: Select diseases of interest

4: Obtain key data

5: Collect health statistics (mortality, incidence or DALYs, for children under five and adults or alternative age groups), for the selected diseases.(3, 15)

6: Assess prevalence of exposure within the study population

7: Estimate the disease burden among non-cases

8: Calculate the population attributable fractions - Use the formula for estimating the population attributable fraction (PAF) for each health outcome:

PAF = [p(RR − 1)]/[p(RR − 1) + 1]

where: p = proportion exposed to the risk factor in the specified age group; RR = relative risk for outcome in a specified population group (22).

9: Calculate attributable burdens - Where attributable burden can be defined as (burden of a given disease in a given population that is identified as due to a specific exposure). Consequently, that portion of disease burden in the population that could be reduced if causative exposure were eliminated. (3)
It equals the number of people in a certain health state as a result of exposure to the (environmental) factor that is being analyzed. (16)

10: Describe uncertainty -
Describe the causes of uncertainty, and analyse the sensitivity of the calculated health burden to the assumptions made.

11: Write summary and conclusions. (3)

Sources Of Uncertainty, and How To Overcome Them

When estimating the environmental burden of disease, a number of potential sources of error may arise. These can come from:

the measure of exposure
the exposure-risk relationship
the assumptions made in applying the exposure or exposure-risk relationship to the country of Concern
the health statistics, and
the expert opinions, if used.

Generally it is not possible to estimate a formal confidence interval, but it is possible to estimate a range of possible values the environmental disease burden may take (a sort of sensitivity analysis), based on different input parameters and assumptions. This analysis is not provided in the preliminary country profiles of the environmental burden of disease, but should be performed in the national process of reviewing these profiles. (4, 2, 3)

Dealing with contextual uncertainty

Results of an assessment are highly related to the definitions and system boundaries chosen.But most of these definitions cannot be harmonized across assessments, because they are related to the purpose of a specific assessment. Few general guidelines can be given to deal with contextual uncertainties. In summary, the chosen definitions and boundaries need to be discussed, reported and consistently used. This process may often need to engage relevant stakeholders. When more than one definition has be made about an element in the assessment, multiple analyses can be run using different sets of definitions. Sensitivity and decision analyses can help to set which sources of uncertainty mostly affect the final results. (4)

Various EBD (environmental burden of disease) studies have assessed the need for uncertainty and sensitivity analyses. For example, these analyses are based primarily on statistical uncertainty of some parameters and input data. Only if both scientists and policy makers comprehend the potential extent of uncertainties and the way they may affect the assessment results, can these assessments result in truly informed policy making.(4)

Implementation and Interpretation

The public health impacts of air pollution (PM10 - annual mean of particulate matter - and ozone), noise, radiation (radon and UV) and indoor dampness were quantified using DALYs (Disability Adjusted Life Years). In DALY calculations, DALYs= number of people with a certain disease * duration of the disease (or loss of life expectancy in case of mortality)* severity of the disorder (varying from 0 for perfect health to 1 for death). According to this equation, morbidity and mortality can be expressed in one similar value, making environmental health problems more or less comparable and providing ways to plan or evaluate environmental health related policies. But DALYs are a simplification of a very complex reality, and therefore only give a very crude indication of environmental health impact. Then researchers appraised which effects are relevant to investigate for each environmental factor, and which data are best to use. Necessary data include prevalence numbers, exposure-response relationships, and weighting factors that give an indication of the severity of a certain disorder. When information is missing or vague, experts will be consulted in order to decide which (alternative) data sources to use. And an uncertainty analysis is carried out in so as to analyze the effects of different assumptions. (16)

Trends in the environmental burden of disease in the Netherlands, 1980 - 2020

Environmental factors can affect health and quality of life of the Dutch population in different ways. Air pollution is associated with respiratory and cardiovascular diseases, noise exposure can cause annoyance, and exposure to certain forms of radiation can lead to the development of cancer. It is difficult to compare these environmental problems, since they differ in type and scope. So it can be useful to quantify the health impact of the environment in an integrated measure. (DALYs) was calculated for the health effects of air pollution, noise, radon, UV and indoor dampness for the period 1980 to 2020. In the Netherlands, roughly 2 to 5 percent of the total disease burden can be attributed to the effect of (short-term) exposure to air pollution, noise, radon, total natural UV and dampness in houses for the year 2000. This percentage can increase to up to 13% due to uncertainty, assuming no threshold. Among the investigated factors, the relatively uncertain effects of long-term PM10 exposure have the greatest impact on public health in the Netherlands. The levels of PM10 are decreasing, and therefore the related disease burden is also expected to decrease. Noise exposure and its associated disease burden is likely increase up to a level where the disease burden is similar to the disease burden attributable to traffic accidents. These rough estimates do not provide a complete picture of the environmental health burden, because data are uncertain, not all environmental-health relationships are known, not all environmental factors have been included, and it was not possible to assess all potential health effects. The effects of a number of these assumptions were evaluated in an uncertainty analysis. (16)

Time trends were studied by making calculations for the past (1980 or 1990) and for the future (2010 or 2020). It was concluded that the disease burden related to PM10 exposure may decrease, the noise-related disease burden will further increase, and the number of DALYs caused by radon and UV radiation is supposed to remain fairly similar. (16)

The environmental burden of disease in Canada: Respiratory disease, cardiovascular disease, cancer, and congenital affliction

Exposure to environmental hazards may cause many chronic diseases, so the magnitude of their contribution to the total disease burden in Canada is not well understood. To calculate the environmental burden of disease in Canada for respiratory disease, cardiovascular disease, cancer, and congenital affliction, the contribution of environmental exposures to the overall burden of disease could play an important role in determining public health and environmental policy priorities. To give an initial estimate of the environmental burden of disease in Canada for four major categories of disease, the EAFs -environmentally attributable fractions- developed by the WHO, EAFs developed by other researchers, and data from Canadian public health institutions were used. (17) Results show that: 10,000–25,000 deaths; 78,000–194,000 hospitalizations; 600,000–1.5 million days spent in hospital; 1.1 million–1.8 million restricted activity days for asthma sufferers; 8000–24,000 new cases of cancer; 500–2500 low birth weight babies; and between $3.6 billion and $9.1 billion in costs happen in Canada each year due to respiratory disease, cardiovascular illness, cancer, and congenital affliction associated with adverse environmental exposures. This suggests that the burden of illness in Canada resulting from adverse environmental exposures is significant. Stronger efforts to avoid adverse environmental exposures are demanded, including research, education, and regulation. (17)

Significance Of Using "Environmental Burden Of Disease

In environmental health research, focus has moved from relatively simple to more complex issues. Environmental health impact assessment has turn into a valuable tool for decision support. These types of assessments increasingly use so-called environmental burden of disease (EBD) measures to express health impacts. The EBD can be seen as the gap – caused by environmental factors – between current health status and an alternative situation in which environmental exposures are reduced or eliminated. Burden of disease evaluation enable comparison of environmental health problems. This successively enables policy makers to set priorities.(2, 3).

There are several other good reasons for performing EBD studies, such as:

1- Answer the following questions:

a- How much disease is caused by climate change?

b- How much could be avoided by making possible reductions in the exposure (avoidable burden of disease)? (18)

2- Develop, evaluate and prioritize Health-related policy measures.

3- Prioritizing actions in health and the environment

4- Setting priorities in health research

5- Planning for preventive action

6- Planning for future needs

7- Comparing action and health gain

8- Enable intra comparisons within regions of the same country, and inter-comparisons among different countries

9- Countries can combine this type of evidence along with information about policies and their costs to decide how to put their health agenda.

10- Assessing performance at national level. (2, 3, 4,18, 19)

By: Dr. Reada, Mayada; Ajlouni, Eham

Ph.D in environmental health; Ph.D student in environmental health

REFERENCES

1-Prüss-Üstün Annette, Corvalán C.(2006) Preventing disease through healthy environments. Towards an estimate of the environmental burden of disease. WHO 2006.

2- David Kay; Annette Prüss; Carlos Corvalán.(2000). Methodology for assessment of Environmental burden of disease. ISEE session on environmental burden of disease, WHO Consultation, Buffalo, 23-24 August 2000.

3- Prüss-Üstün A, et al. Introduction and methods: assessing the environmental burden of disease at national and local levels. Geneva, World Health Organization, 2003. (WHO Environmental Burden of Disease Series, No. 1).

4- Anne B Knol, Arthur C Petersen, Jeroen P van der Sluijs and Erik Lebret (2009). Dealing with uncertainties in environmental burden of disease assessment. Available at: http://www.ehjournal.net/content/8/1/21

5- David Briggs. Environmental pollution and the global burden of disease. Br Med Bull (2003) 68 (1): 1-24.This article appears in:Impact of environmental pollution on health: Balancing risk. Available at :http://bmb.oxfordjournals.org/content/68/1/1.short

6- About the Global Burden of Disease (GBD) project. Available at: http://www.who.int/healthinfo/global_burden_disease/about/en/index.html

7- Global burden of disease. Available at: http://www.who.int/topics/global_burden_of_disease/en/

8- WHAT IS THE ENVIRONMENT IN THE CONTEXT OF HEALTH?. http://www.who.int/quantifying_ehimpacts/publications/preventingdisease2.pdf

9- Quantification of the disease burden attributable to environmental risk factors. (2010). Programme on quantifying environmental heath impacts, Department of Public Health and Environment, World Health Organization, Switzerland. http://www.who.int/quantifying_ehimpacts/summaryEBD_updated.pdf

10- Öberg M, Jaakkola MS, Prüss-Üstün A, Schweizer C, Woodward A. (2010) Second-hand smoke: Assessing the environmental burden of disease at national and local levels. Geneva, World Health Organization (WHO Environmental Burden of Disease Series, No. 18).

11- Mattias Öberg, Maritta S Jaakkola, Alistair Woodward, Armando Peruga, Annette Prüss-Ustün. Worldwide burden of disease from exposure to second-hand smoke: a retrospective analysis of data from 192 countries. Available at: http://www.who.int/quantifying_ehimpacts/publications/smoking.pdf. Published Online November 26, 2010.

12- By Robyn Lucas. Solar ultraviolet radiation: Assessing the environmental burden of disease at national and local levels. Environmental burden of disease series, No. 17. available at: http://www.who.int/quantifying_ehimpacts/publications/ebd17

13- Quantifying environmental health impacts. Available at: http://www.who.int/quantifying_ehimpacts/en/

14- Knol AB, Staatsen BAM. (2005) Trends in the environmental burden of disease in the Netherlands, 1980 – 2020. RIVM rapport 500029001 http://www.rivm.nl/bibliotheek/rapporten/500029001.html

15- Fewtrell L, Prüss-ـstün A, Bos R, Gore F, Bartram. Water, sanitation and hygiene: quantifying the health impact at national and local levels in countries with incomplete water supply and sanitation coverage. World Health Organization, Geneva, 2007. (WHO Environmental Burden of Disease Series No. 15)

16- AB Knol, BAM Staatsen (2005). Trends in the environmental burden of disease in the Netherlands 1980 – 2020. RIVM report 500029001 .

17- David Boyd, Stephen J. Genuis. (2007). Study: Environmental burden of disease in Canada. the November issue of The Ring, a UVic community paper. Available at:http://www.greenparty.ca/fr/node/3079

18- Environmental Burden of Disease Assessment. From McMichael, A.J. et al. 2003. Climate change. In Global Burden of Disease. C.J. Murray and A.D. Lopez (eds.). World Health Organization, Geneva. WHO. 2003. The World Health Report 2002.

19- The WHO guides on assessing the environmental burden of disease. available at: http://www.who.int/quantifying_ehimpacts/publications/en/9241546204chap1.pdf.

20- Annette Prüss and Arie Havelaar. (2001) The Global Burden of Disease study and applications in water, sanitation and hygiene. From 2001 World Health Organization (WHO). Water Quality: Guidelines, Standards and Health. Edited by Lorna Fewtrell and Jamie Bartram. Published by IWA Publishing, London, UK.

21- WHO. Health statistics and health information systems . Metrics: Disability-Adjusted Life Year (DALY). Quantifying the Burden of Disease from mortality and morbidity. Available at: http://www.who.int/healthinfo/global_burden_disease/metrics_daly/en/index.html

22- WHO. Health statistics and health information systems. Metrics: Population Attributable Fraction (PAF). Quantifying the contribution of risk factors to the Burden of Disease. Available on: http://www.who.int/healthinfo/global_burden_disease/metrics_paf/en/index.html

Eham.ajlouni

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