Household Dust Contains Bacteria That May Trigger Asthma Symptoms

Researchers at NIEHS and the University of Iowa found a strong association between endotoxin levels and the prevalence of diagnosed asthma, asthma medication use, asthma symptoms, and wheezing. These relationships were strongest for dust found on the bedroom floor and bedding. Households with higher endotoxin concentrations experienced higher prevalence of respiratory and asthma related symptoms.

Endotoxins are found in the cell wall of bacteria and are only released when bacteria ruptures or disintegrates. Because bacteria, particularly from dust, can be found everywhere in the home, the likelihood of endotoxin release is high. Once released, endotoxins can cause inflammation of the airways and lead to asthma symptoms.

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

To conduct the research, two research assistants visited each household, administered a detailed questionnaire, conducted a home inspection, and used a standardized protocol to collect samples. Dust samples were collected from various sections of the home, the bedroom, kitchen and living room floors, bedding, and upholstered furniture. The samples were then analyzed for endotoxin. A disease association analysis was performed to correlate endotoxin concentrations to specific health outcomes.

“When we analyzed the dust samples, we found that kitchen and living room floors had the highest concentrations of endotoxin,” said Darryl C. Zeldin, M.D., an NIEHS Senior Investigator. “However, when we looked at where the health impact of the dust was the most significant, we found that the likelihood of having recent asthma symptoms was nearly three times greater among individuals with exposure to high levels of endotoxin in the bedroom.”

The researchers found that all dust samples contained detectable levels of endotoxin. The average concentration of endotoxin ranged from 80.5 units per milligram of dust on kitchen floors to 18.7 units per milligram of dust on bedding. The dust collected from family room floors had endotoxin concentrations of 63.9 units per milligram of dust; sofas had concentration levels at 44.8; and 35.3 units 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 author on the paper. "This suggests that exposure to endotoxin increases asthma risk even in non-allergic individuals."

Since the mid 1960s, researchers knew that house dust contains endotoxin, but it is only within the last five years that they began to understand the impact of household endotoxin on human health, particularly respiratory health. Knowing what triggers asthma, whether it is endotoxins or something else, may help a physician better prevent or treat symptoms.

“This study implies that it is not just the concentration of the endotoxin that matters,” added Dr. Schwartz, Director of NIEHS. “Understanding how factors such as duration of exposure, timing of the exposure, and genetic factors, contribute to the development of diseases like asthma will lead to new insights into how to prevent and treat this important disease.” NIEHS is implementing new research studies to better understand the role that the indoor environment plays in the development and severity of asthma.

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