New University of Iowa research demonstrates that interactions between indoor and outdoor air pollution contribute to increased emergency room visits for asthma in both children and adults.

The research by investigators in the UI College of Public Health is the first nationwide study to examine children and adults co-exposed to house dust endotoxin and outdoor air pollutants such as ozone, nitrogen dioxide, and particulate matter. Endotoxins are molecules found in the outer membrane of common bacteria that cause inflammation in the airways of animals and humans.

Investigators studied 6,488 participants in the 2005-2006 National Health and Nutrition Examination Survey (NHANES). Dust collected from bedding and bedroom floors was analyzed at the UI for endotoxin, while modeled and monitored air pollution data were used to estimate annual average ambient pollution exposure levels at participants’ homes.

The analysis found that among all study participants, co-exposure to elevated levels of house dust endotoxin and particulate matter was associated with a five-fold increase in emergency room visits for asthma in the preceding 12 months. Meanwhile, exposure to higher endotoxin and nitrogen dioxide concentrations was associated with increased ER visits in children.

“We have previously established that indoor endotoxin exposure exacerbates asthma. This new research demonstrates that the combined exposures of endotoxin and ambient air pollution send people to the emergency room even at exposure levels that are considered safe,” says Peter Thorne, UI professor and head of occupational and environmental health and senior author on the paper, recently published in the American Journal of Respiratory and Critical Care Medicine. Thorne also directs the UI Environmental Health Sciences Research Center.

The research team also includes Angelico Mendy, former UI doctoral student now working at the National Institutes of Health; Darryl Zeldin and Päivi Salo from the National Institute of Environmental Health Sciences; and scientists at the U.S. Department of Health and Human Services and Social & Scientific Systems, Inc.

The researchers suggest additional studies to examine the association of co-exposures to household endotoxin and ambient air pollution with other respiratory conditions, including chronic obstructive pulmonary disease. If further research confirms such associations, Thorne says, future public health interventions targeting both exposures may be more effective than measures aimed at individual triggers.

An accompanying editorial in the journal noted that the concentrations of ozone, nitrogen dioxide, and particulate matter examined in the UI study were well below the U.S. EPA National Ambient Air Quality standards for annual averages.

“The confirmation of health effects at concentrations below current standards emphasizes the importance of adequately protecting our patients with chronic lung diseases,” notes the editorial. “If anything, after considering other recent studies, ambient air quality standards need to be further strengthened.”