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University of Iowa News Release

Dec. 9, 2004

Increased Asthma Found Among Iowa Children Living On Hog Farms

New research conducted by investigators in the University of Iowa College of Public Health has found that the prevalence of asthma is elevated among children living on farms where swine are raised. Children living on swine farms where antibiotics are added to feed have a significantly higher prevalence of the respiratory disease, according to the UI study.

The research, led by James A. Merchant, M.D., dean of the College of Public Health and professor of occupational and environmental health, is reported in the journal Environmental Health Perspectives.

"Farms that added antibiotics to feed tended to have larger numbers of livestock than farms that did not add antibiotics to feed," Merchant observed. "The addition of antibiotics may serve as an indicator of larger swine operations, however, it is plausible that this route of antibiotic exposure may play some causal role in the development of childhood asthma. We believe that some of the increase in asthma risk is related to occupational and bystander exposures in animal feeding operations."

Researchers examined 644 children ranging in age from birth through 17 years living in Keokuk County, Iowa, to determine links between farm and other environmental risk factors and asthma. In addition to identifying the risk of living on farms that raise swine and add antibiotics to feed, several "early life events," including premature birth, a respiratory infection under age 3 and high-risk birth were also associated with asthma. Other risk factors identified include male gender, age, personal history of allergies and family history of allergic disease.

"Asthma is a multifactorial disease involving the complex interaction of genetic and environmental determinants," Merchant said. "This tends to make epidemiologic investigations of farm-related asthma very difficult. The results of this study are all the more meaningful because we have taken into account multiple personal and other environmental risk factors."

Merchant said results of this study should heighten swine farm parents' awareness that their children may face increased asthma risk and therefore should take precautions to reduce children's respiratory exposures from animal feeding operations.

Although the study was not designed to address the question of whether exposures to dust, irritant gases and odors arising from large-scale animal feeding operations are associated with respiratory problems among children and rural residents living near such facilities, Merchant said that remains an important research priority.

The research team also included UI College of Public Health investigators Kevin Kelly, Ph.D., Leon Burmeister, Ph.D. Ann Stromquist, Ph.D., Craig Taylor, Peter Thorne, Ph.D., Wayne Sanderson, Ph.D., and Elizabeth Chrischilles, Ph.D. Other investigators were Allison Naleway, Ph.D., of Kaiser Permanente Northwest; Erik Svendsen, Ph.D., of the U.S. Environmental Protection Agency; and Stephen Reynolds, Ph.D., of Colorado State University. 

The full report may be accessed online at the Environmental Health Perspectives website at

STORY SOURCE: The University of Iowa College of Public Health, Office of Communications, 4261 Westlawn, Iowa City, Iowa 52242.

MEDIA CONTACT: Dan McMillan, 319-335-6835,

GRAPHIC: A chart showing prevalences of asthma in rural Iowa children, according to their living environments, is available for downloading at