Indicator 3.9.1: Mortality rate attributed to household and ambient air pollution (per 100 000 population)

As part of a broader project to assess major risk factors to health, the burden of disease resulting from both, exposure to ambient (outdoor) air pollution and household (indoor) air pollution from polluting fuel use for cooking, was assessed. Ambient air pollution results from emissions from industrial activity, households, cars and trucks which are complex mixtures of air pollutants, many of which are harmful to health. Of all of these pollutants, fine particulate matter has the greatest effect on human health. By polluting fuels is understood solid fuels such as wood, coal, animal dung, charcoal, and crop wastes and also kerosene. The majority of the burden due to household air pollution is borne by the populations in low and middle-income countries.In high-income countries, urban outdoor air pollution ranks in the top ten risk factors to health, and is the first environmental risk factor.

The burden of disease attributable to joint effects of household and ambient air pollution can be expressed as: death rate (both crude and age-standardized). Death rates are calculated by dividing the number of deaths by the total population. Age-standardized rates adjust for differences in population age distribution by applying the observed age-specific mortality rates for each population to a standard population. The age-standardized rates can therefore be used to compare the rates of countries without being affected by the differences in age distribution from country to country. Evidence from epidemiological studies have shown that exposure to air pollution is linked, among others, to the important diseases taken into account in this estimate: 1) Lower respiratory infections in general population; 2) Stroke in adults (25 years and over); 3) Ischaemic heart diseases in adults (25 years and over); 4) Chronic obstructive pulmonary diseases in adults (25 years and over); and 5) Trachea, bronchus and lung cancers in adults (25 years and over).

Estimates are available by age group and by sex.

Impact

Burden of disease is calculated by first combining information on the increased (or relative) risk of a disease resulting from exposure, with information on how widespread the exposure is in the population (in this case, the annual mean concentration of particulate matter to which the population is exposed). This allows calculation of the 'population attributable fraction' (PAF), which is the fraction of disease seen in a given population that can be attributed to the exposure, in this case the annual mean concentration of particulate matter. Applying this fraction to the total burden of disease (e.g. cardiopulmonary disease expressed as deaths), gives the total number of deaths or that results from ambient air pollution.

For death rates, the country deaths are summed according to the region of interest and divided by the corresponding regional population.

Main references: - Brauer M, Amann M, Burnett RT, Cohen A, Dentener F, Ezzati M, et al. Exposure assessment for estimation of the global burden of disease attributable to outdoor air pollution. Environ Sci Technol. 2012;46(2):652-60. doi: 10.1021/es2025752. - Burnett RT, Pope A, Ezzati M, Olives C, Lim SS, Mehta S, et al. An intgrated risk function for estimating the global burden of disease attributable to ambient fine particulate matter exposure. Environ Health Perspect. 2014. doi: 10.1289/ehp.1307049. - Lim SS, Vos T, Flaxman AD, Danaei G, Shibuya K, Adair-Rohani H, et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010. The Lancet. 2012;380(9859):2224-60. doi: 10.1016/S0140-6736(12)61766-8. - Ezzati M, Hoorn SV, Rodgers A, Lopez AD, Mathers CD, Murray CJ. Comparative Risk Assessment Collaborating Group. Estimates of global and regional potential health gains from reducing multiple major risk factors. The Lancet. 2003 Jul 26;362(9380):271-80. doi: 10.1016/s0140-6736(03)13968-2.

[email protected]

Sophie Gumy

An approximation of the combined effects of risk factors is possible if independence and little correlation between risk factors with impacts on the same diseases can be assumed (Ezzati et al 2003). In the case of air pollution, however, there are some limitations to estimate the joint effects: limited knowledge on the distribution of the population exposed to both household and ambient air pollution, correlation of exposures at individual level as household air pollution is a contributor to ambient air pollution, and non-linear interactions. In several regions, however, household air pollution remains mainly a rural issue, while ambient air pollution is predominantly an urban problem. Also, in some continents, many countries are relatively unaffected by household air pollution, while ambient air pollution is a major concern. If assuming independence and little correlation, a rough estimate of the total impact can be calculated, which is less than the sum of the impact of the two risk factors. The joint effects of both ambient and household air pollution would result in the impacts shown in the present table. Given the limitations, however, the estimates presented should be interpreted with caution, and provide indicative values only.