A study by a multi-disciplinary team of COEH scientists concludes that reducing indoor air pollution from wood-burning stoves substantially decreases childhood pneumonia — the leading cause of death for children less than 5 years of age. These latest findings offer compelling evidence that wood smoke is a major risk factor for pneumonia in the households of the estimated three billion people who rely on solid fuel for indoor cooking and heating.
Although earlier studies have linked exposure to household smoke to respiratory infections, the study published by lead author Kirk Smith and co-investigators John Balmes and Lisa Thompson is the first randomized controlled trial on indoor particulate air pollution. Conducted in the San Marcos region of rural highland Guatemala, the study enrolled 534 households with a pregnant woman or young infant between October 2002, and December 2004. Approximately half of the households were randomly assigned a woodstove with a chimney. The remaining households formed the control group and continued to cook with traditional, unventilated stoves. On completion of the study, the research team gave all participants the chimney stove.
There were 149 cases of physician diagnosed pneumonia in intervention households and 180 cases in control households during the monitoring period. Nine out of 23 childhood deaths in the study were assigned to pneumonia — three occurred in the intervention group and six in the control group.
Air pollution measurements in a random sample of households showed carbon monoxide (CO) concentrations in the kitchen were about 90% lower in chimney stove households compared to control households. The chimney stove was associated with just a 50% reduction in actual exposure, however, based on multiple personal air pollution measurements on all children. Nevertheless, this reduction was associated with a reduced relative risk of 18% for physician-diagnosed pneumonia and 28% for physician-diagnosed severe pneumonia, defined as being accompanied by low oxygen saturation in the child’s blood.1
“Reducing household wood smoke exposure seems to offer as much benefit as vaccinations and nutrition supplements for reducing severe pneumonia. Substantial additional investment is now needed to find ways to do so effectively for large populations,” Smith said.
The study adds evidence to support the Global Alliance for Clean Cookstoves, an initiative of the United Nations Foundation backed by Secretary of State Hillary Clinton. It calls for 100 million households to adopt clean and efficient cookstoves and fuels by 2020.
Kirk Smith is a professor of global environmental health at UC Berkeley School of Public Health. John Balmes is director of COEH and division chief of Occupational and Environmental Medicine at San Francisco General Hospital. Lisa Thompson is an assistant professor in the School of Nursing at UCSF. The study was funded by the U.S. National Institute of Environmental Health Sciences and the World Health Organization.
1 Smith KR, McCracken JP, Weber MW, Hubbard A, Jenny A, Thompson LM, Balmes J, Diaz A, Arana B, Bruce N. Effect of reduction in household air pollution on childhood pneumonia in Guatemala (RESPIRE): a randomized controlled trial. Lancet. 2011 Nov 12;378(9804):1717-26.
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