June 24, 2009
Increased household endotoxin associated with poverty, people, pets
People with asthma often pay close attention to potential allergens lurking outdoors, but University of Iowa research shows they also may want to be wary of dust indoors that can contain endotoxin, a potent inflammatory agent that is a component of many types of bacteria.
A nationwide study of household dust has identified a number of factors associated with increased residential endotoxin, including poverty, people, pets, cleanliness and geography. The findings appear in the May 2009 issue of Environmental Health Perspectives.
As part of the National Survey of Lead and Allergens in Housing, more than 2,500 dust samples were collected from multiple locations within more than 800 housing units nationwide. Researchers at the UI Environmental Health Sciences Research Center and the National Institute of Environmental Health Sciences examined the samples for endotoxin, which is thought to trigger asthma and asthma-related symptoms.
"Few studies focus on the endotoxin level predictors, and this is the first to evaluate domestic endotoxin levels over a wide geographic region and across demographic groups," said Peter Thorne (left), director of the UI Environmental Health Sciences Research Center and professor of occupational and environmental health in the UI College of Public Health. "While allergens, such as those from cockroaches, cats or dogs, have obvious sources, endotoxin does not. Our study identified a distinct set of predictors of endotoxin, including regional and socioeconomic factors."
The study found that endotoxin levels depend on sampling location within the home and region of the country.
Among the study's nine census divisions, the Pacific division -- including California, Oregon and Washington -- was found to have the highest endotoxin levels. The New England division -- including Connecticut, Massachusetts, Maine, New Hampshire, Rhode Island and Vermont -- had the lowest documented endotoxin concentrations.
Notably, the study found increased occupancy had a very strong relationship with increased endotoxin, particularly in family room floor samples. Presence of children was also a factor, increasing endotoxin in samples from bedroom floors, family room floors and bedding. Pet ownership was also significantly associated with endotoxin.
"Humans and pets harbor dead and dormant bacteria composed of endotoxin in the gut and on the skin, from which they are shed. Thus, it is logical that larger families, children in the home, and pet ownership contribute to household endotoxin," Thorne said.
Another household factor relating to endotoxin was living in poverty, for which bedroom floor and bedding endotoxin levels were 56 percent and 58 percent higher than in non-impoverished households, respectively.
Cleanliness was a factor, as well. In walk-through surveys conducted by field staff, it was noted that evidence of smoking, cockroach stains and food debris predicted increased endotoxin in bedroom and family room floor samples.
Contrary to studies of mold and mildew, the investigation found no effect on endotoxin concentration from seasonal variations or dehumidifier use.
"This study identifies a number of factors that produce higher endotoxin levels that could help guide public health professionals to aid in reducing endotoxin exposure," Thorne said. "Interventions should include eliminating cockroach infestations, reducing cigarette smoking indoors, and improving housing conditions and cleanliness, particularly in homes with multiple occupants and pets.
"In addition to lowering endotoxin exposure, these interventions would reduce exposures to other allergens and asthma triggers," he added.
The study was supported by a National Institute of Environmental Health Sciences grant and the U.S. Department of Housing and Urban Development’s Office of Healthy Homes and Lead Hazard Control.
More information about the Environmental Health Sciences Research Center, based in the UI College of Public Health, can be found at http://www.ehsrc.uiowa.edu/. More information about the National Institute of Environmental Health Sciences can be found at http://www.niehs.nih.gov/.
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