Acute respiratory infections (ARI) are the leading cause of burden of disease worldwide and have been causally linked with exposure to pollutants from domestic biomass fuels in developing countries. We used longitudinal health data coupled with detailed monitoring and estimation of personal exposure from more than 2 years of field measurements in rural Kenya to estimate the exposure-response relationship for particulates [is less than] 10 [micro]m diameter ([PM.sub.10]) generated from biomass combustion. Acute respiratory infections and acute lower respiratory infections are concave, increasing functions of average daily exposure to [PM.sub.10], with the rate of increase declining for exposures above approximately 1,000-2,000 [micro]g/[m.sup.3]. This first estimation of the exposure-response relationship for the high-exposure levels characteristic of developing countries has immediate and important consequences for international public health policies, energy and combustion research, and technology transfer efforts that affect more than 2 billion people worldwide. Key words: acute respiratory infections, Africa, biomass combustion, developing countries, exposure-response relationship, field study, indoor air pollution, particulate matter, public health. Environ Health Perspect 109:481-488 (2001). [Online 4 May 2001]
Acute respiratory infections (ARI) are the leading cause of the global burden of disease and account for more than 6% of the global burden of disease and mortality, mostly in developing countries (Figure 1) (1). Between 1997 and 1999, acute lower respiratory infections (ALRI) were the leading cause of mortality from infectious diseases, with an estimated 3.5-4.0 million deaths worldwide (1-3). Exposure to indoor air pollution, especially to particulate matter, from the combustion of biofuels (wood, charcoal, agricultural residues, and dung) has been implicated as a causal agent of respiratory diseases in developing countries (4-9). This association, coupled with the fact that globally more than 2 billion people rely on biomass as the primary source of domestic energy, has put preventive measures to reduce exposure to indoor air pollution high on the agenda of international development and public health organizations (10-13). The evaluation of the benefits and effectiveness of measures that aim to reduce these negative health impacts, such as design and dissemination of improved stoves and fuels, requires knowledge of the exposure-response relationship between indoor particulate matter from biomass combustion and ARI.
Epidemiologic and physiologic studies over the past two decades in urban areas of industrialized countries have resulted in significant progress in identifying and quantifying the health impacts of outdoor (ambient) particulate matter (14-24). These results however, are applicable to a small range of exposures, generally below 200 [micro]g/[m.sup.3], which are primarily of concern in industrialized countries (12). [The latest U.S. Environmental Protection Agency National Ambient Air Quality Standards, for instance, required the concentration of [PM.sub.10] (particulate matter [is less than] 10 [micro]m) to achieve a 24-hr average [is less than] 150 [micro]g/[m.sup.3])]. There is little information on the shape of the exposure-response relationship at concentrations of hundreds to thousands of micrograms per cubic meter that are commonly observed in indoor environments in developing countries (13). This is a critical gap in our understanding of the role of exposure to particulate matter as a causal agent of ARI, and thus as a contributor to the global burden of disease, because approximately 80% of total global exposure to this pollutant occurs indoors in developing nations (25,26).
Research on the health impacts of indoor air pollution in developing countries has been hindered by a lack of detailed data on both exposure and illness outcomes. …