Indoor air pollution from biomass combustion and acute respiratory infections in Kenya: an exposure-response study.

BACKGROUND Acute respiratory infections (ARI) are the leading cause of the global burden of disease and have been causally linked with exposure to pollutants from domestic biomass fuels in less-developed countries. We used longitudinal health data coupled with detailed monitoring of personal exposure from more than 2 years of field measurements in rural Kenya to estimate the exposure-response relation for particulates smaller than 10 mm in diameter (PM(10)) generated from biomass combustion. METHODS 55 randomly-selected households (including 93 infants and children, 229 individuals between 5 and 49 years of age, and 23 aged 50 or older) in central Kenya were followed up for more than 2 years. Longitudinal data on ARI and acute lower respiratory infections (ALRI) were recorded at weekly clinical examinations. Exposure to PM(10) was monitored by measurement of PM(10) emission concentration and time-activity budgets. FINDINGS With the best estimate of the exposure-response relation, we found that ARI and ALRI are increasing concave functions of average daily exposure to PM(10), with the rate of increase declining for exposures above about 1000-2000 mg/m(3). After we had included high-intensity exposure episodes, sex was no longer a significant predictor of ARI and ALRI. INTERPRETATION The benefits of reduced exposure to PM(10) are larger for average exposure less than about 1000-2000 mg/m(3). Our findings have important consequences for international public-health policies, energy and combustion research, and technology transfer efforts that affect more than 2 billion people worldwide.