Tallying the bills of mortality from air pollution

Since John Graunt's analyses of the Bills of Mortality in London, UK, in 1662, observations of premature deaths have driven public health actions—from John Snow's apocryphal removal of the handle on the Broad Street pump during the 1854 cholera outbreak to the international response to the 2013–16 outbreak of Ebola virus disease in west Africa. The hazard of air pollution episodes was evident in the 4000 excess deaths (revised to 12 000 deaths)during the Great Smog of 1952 in London. However, measuring the cumulative health burden of living with chronically high air pollution is more difficult. As Geoffrey Rose noted, “the cause that is universally present has no influence at all on the distribution of disease, and it may be quite unfindable by the traditional methods”.Nevertheless, findings from large prospective cohort studies in the USA, Canada, and Europe have consistently shown that fine particleand, to a lesser extent, ozone air pollution are associated with increased mortality. Based on this evidence and air pollution monitoring in the UK, the Committee on the Medical Effects of Air Pollutants estimated that loss-of-life expectancy equivalent to 29 000 deaths was attributable to fine particles in 2008, although, as they pointed out, the uncertainties in estimates of attributable deaths may be substantial. In The Lancet, Aaron Cohen and colleagues used global population-weighted mean concentrations of particle mass with aerodynamic diameter less than 2·5

μm (PM2

·5) and ozone and integrated exposure–response functions to estimate the relative risk of mortality from ischaemic heart disease, stroke, chronic obstructive pulmonary disease, lung cancer, and lower respiratory infections. They report that 4·2 million deaths (95% uncertainty interval [UI] 3·7 million to 4·8 million) globally were attributable to fine particles and another 254 000 (97 000 to 422 000) to surface ozone in 2015. Using the same methods, they computed country-specific deaths and disability-adjusted life-years lost attributable to particulate and ozone air pollution for 1990 through 2015. For example, they estimated 27 200 (20 500 to 34 900) deaths in the UK in 2015 were attributable to fine particles and an additional 1400 (500 to 2500) were attributable to ozone. Cohen and colleagues report that China and India, with the largest populations and commensurately high levels of pollution, had the largest estimated numbers of deaths attributable to air pollution: 1·11 million (95% UI 0·95 million to 1·27 million) and 1·09 million (0·94 million to 1·25 million), respectively, in 2015. Similar numbers have been estimated previously. Although the numbers of deaths are not as large as in China and India, the proportions of deaths attributable to air pollution were similarly high in neighbouring countries on the Indian subcontinent. Moreover, Cohen and colleagues estimate that the highest mortality rates attributable to fine particles were in countries in central Asia, where air pollution has not been measured. Advances in remote sensing by satellites and air pollution modelling permit estimates of fine particle air pollution at 11 km × 11 km resolution. When coupled with the geographical distribution of the population, these methods can produce reliable estimates of exposure to fine particles.10 Therefore, estimation of the disease burden of air pollution is feasible in countries or even cities with few or no direct measurements of air pollution. Such estimations also require extrapolation of epidemiological evidence from developed countries to the higher air pollution exposures in the developing world. Borrowing information from studies of analogous fine particle exposures to household air pollution, second-hand smoke, and active smoking provides a framework for extrapolation that is internally consistent across a range of inhaled doses.

The Lancet

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