Bacteria In Household Dust May Trigger Asthma Symptoms

Researchers at NIEHS and the University of Iowa found a strongassociation between endotoxin levels and the prevalence of diagnosedasthma, asthma symptoms, asthma medication use, and wheezing. Theserelationships were strongest for bedroom floor and bedding dust.Households with higher endotoxin concentrations experienced higherprevalence of respiratory symptoms.

Endotoxins are found in the cell wall of bacteria and are only releasedwhen bacteria ruptures or disintegrates. Because bacteria can be foundeverywhere in the home, the likelihood of their release is high. Oncereleased, endotoxins can cause inflammation of the airways and lead toasthma symptoms.

The study, published online in the American Journal of Respiratory andCritical Care Medicine, was conducted using samples from The NationalSurvey of Lead and Allergens in Housing (NSLAH).

Two research assistants visited each household, administered a detailedquestionnaire, conducted a home inspection, and used a standardizedprotocol to collect samples. Dust samples were collected from bedroom,kitchen and living room floors, bedding, and upholstered furniture andassayed for endotoxin. A disease association analysis was performed tocorrelate endotoxin concentrations to specific health outcomes.

"When we analyzed the dust samples, we found that kitchen and livingroom floors had the highest concentrations of endotoxin," said DarrylC. Zeldin, M.D., a Senior Investigator at NIEHS. "However, when welooked at where the health impact of the dust was the most significant,we found that the likelihood of having recent asthma symptoms wasnearly three times greater among individuals with exposure to highlevels of endotoxin in the bedroom."

The researchers found that all dust samples contained detectable levelsof endotoxin. The average concentration of endotoxin ranged from 80.5units per milligram of dust on kitchen floors to 18.7 on bedding.Family room floors had endotoxin concentrations of 63.9 units permilligram of dust; sofas had concentration levels at 44.8; and 35.3units on bedroom floors.

"Interestingly, endotoxin exposure worsens asthma symptoms in adults,regardless of whether an individual has allergies or not" said Peter S.Thorne, Ph.D., a researcher at the University of Iowa and lead authoron the paper. "This suggests that exposure to endotoxin increasesasthma risk even in non-allergic individuals."

Since the mid 1960s, researchers knew that house dust containsendotoxin, but it is only within the last five years that they began tounderstand the impact of household endotoxin on human health. Knowingwhat triggers asthma, whether it is endotoxins or something else, mayhelp a physician better prevent or treat symptoms.

"This study implies that it is not just the concentration of theendotoxin that matters," added Dr. Schwartz, Director of NIEHS."Understanding how factors such as duration of exposure, timing of theexposure, and genetic factors, contribute to the development ofdiseases like asthma will lead to new insights into how to prevent andtreat this important disease." NIEHS is implementing new studies tobetter understand the role that the indoor environment plays in thedevelopment and severity of asthma.

NIEHS, a component of the National Institutes of Health, supportsresearch to understand the effects of the environment on human health.For more information about asthma please visit our website at http://www.niehs.nih.gov/airborne/. For more information on other environmental health topics, please visit our website at http://www.niehs.nih.gov/.