Measuring Health and Disease

Measuring Health and Disease I: Introduction to Epidemiology Module Guide

This module was designed to meet the growing need for an applied course in the measurement of a variety of health indicators and outcomes. Whether you manage a healthprogramme, a health facility, or simply have to interpret health data in the course of your work, this module sets out to increase your capacity to deal with health and disease information. It aims to assist you in applying epidemiological knowledge and skills to a variety of Public Health problems such as:

• Is your DOTS programme succeeding?
• What does it mean if a TB prevalence is 850/100 000?
• Is this a Public Health problem or not?
• What is the “burden of disease” in different communities?

Disease burden

Disease burden is the impact of a health problem as 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), both of which quantify the number of years lost due to disease. One DALY can be thought of as one year of healthy life lost, and the overall disease burden can be thought of as a measure of the gap between current health status and the ideal health status (where the individual lives to old age free from disease and disability).^[1][2][3] The environmental burden of disease is defined as the number of DALYs that can be attributed to environmental factors.^[3][4][5] These measures allow for comparison of disease burdens, and have also been used to forecast the possible impacts of health interventions.

Implementation and interpretation

The public health impacts of air pollution (annual means of PM10 and ozone), noise pollution, and radiation (radon and UV), can be quantified using DALYs. For each disease, a DALY is calculated as:

DALYs = number of people with the disease × duration of the disease (or loss of life expectancy in the case of mortality) × severity (varying from 0 for perfect health to 1 for death)

Necessary data include prevalence data, 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. An uncertainty analysis is carried out so as to analyze the effects of different assumptions.^[15]

Uncertainty[edit]

When estimating the environmental burden of disease, a number of potential sources of error may arise in the measure of exposure and exposure-risk relationship, assumptions made in applying the exposure or exposure-risk relationship to the relevant country, health statistics, and, if used, expert opinions.

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 based on different input parameters and assumptions. When more than one definition has to be made about a certain element in the assessment, multiple analyses can be run, using different sets of definitions. Sensitivity and decision analyses can help determine which sources of uncertainty affect the final results the most.

Representative examples

The Netherlands

In the Netherlands, air pollution is associated with respiratory and cardiovascular diseases, and exposure to certain forms of radiation can lead to the development of cancer. Quantification of the health impact of the environment was done by calculating DALYs for air pollution, noise, radon, UV, and indoor dampness for the period 1980 to 2020. In the Netherlands, 2–5% of the total disease burden in 2000 could be attributed to the effects of (short-term) exposure to air pollution, noise, radon, natural UV radiation, and dampnessin houses. The percentage can increase to up to 13% due to uncertainty, assuming no threshold.

Among the investigated factors, long-term PM10 exposure have the greatest impact on public health. As levels of PM10 decrease, related disease burden is also expected to decrease. Noise exposure and its associated disease burden is likely to increase to a level where the disease burden is similar to that of traffic accidents. The 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.^[15]

Canada

Exposure to environmental hazards may cause chronic diseases, so the magnitude of their contribution to the Canada's total disease burden is not well-understood. In order to give an initial estimate of the environmental burden of disease for four major categories of disease, the EAF developed by the WHO, EAFs developed by other researchers, and data from Canadian public health institutions were used.^[17] Results showed a total of 10,000–25,000 deaths, with 78,000–194,000 hospitalizations; 600,000–1.5 million days spent in hospital; 1.1–1.8 million restricted activity days for sufferers of asthma; 8000–24,000 new cases of cancer; 500–2,500 babies with low birth weights; and C$3.6–9.1 billion in costs each year due to respiratory disease, cardiovascular illness, cancer, and congenital affliction associated with adverse environmental exposures.^[17]

Criticism[edit]

DALYs are a simplification of a complex reality, and therefore only give a crude indication of environmental health impact. Relying on DALYs may make donors take a narrow approach to health care programs. Foreign aid is most often directed at diseases with the highest DALYs, ignoring the fact that other diseases, despite having lower DALYs, are still major contributors to disease burden. Less-publicized diseases thus have little or no funding for health efforts. For example, maternal death (one of the top three killers in most poor countries) and pediatric respiratory and intestinal infections maintain a high disease burden, and safe pregnancy and the prevention of coughs in infants do not receive adequate funding.

Disease burden methodologies such as DALYs also do not capture other aspects of disease and illness, such as pain and suffering, deterioration in quality of life, and emotional and physical impacts on families