|Bacteria in Household Dust May Trigger Asthma Symptoms
New research shows that bacteria lurking in household dust produce chemicals
that may trigger asthma and asthma-related symptoms such as wheezing. These bacterial
chemicals, called endotoxins, particularly those found on bedroom floors, were
linked with increased respiratory problems in adults. This study, supported by
the National Institute of Environmental Health Sciences (NIEHS), a part of the
National Institutes of Health, is the first nationwide study of endotoxins in
the household environment, and it involved analysis of more than 2,500 dust samples
from 831 homes across the U.S.
Researchers at NIEHS and the University of Iowa found a strong association between
endotoxin levels and the prevalence of diagnosed asthma, asthma symptoms, asthma
medication use, and wheezing. These relationships were strongest for bedroom
floor and bedding dust. Households with higher endotoxin concentrations experienced
higher prevalence of respiratory symptoms.
Endotoxins are found in the cell wall of bacteria and are only released when
bacteria ruptures or disintegrates. Because bacteria can be found everywhere
in the home, the likelihood of their 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).
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 bedroom, kitchen and living room floors, bedding,
and upholstered furniture and assayed 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., a
Senior Investigator at NIEHS. “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 on bedding. 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. Knowing what triggers asthma, whether
it is endotoxins or something else, may help a physician better prevent or treat
“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 studies
to better understand the role that the indoor environment plays in the development
and severity of asthma.
NIEHS, a component of the National Institutes of Health, supports research
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/.
The National Institutes of Health (NIH) — The Nation's Medical Research
Agency — includes 27 Institutes and Centers and is a component of
the U. S. Department of Health and Human Services. It is the primary Federal
agency for conducting and supporting basic, clinical, and translational medical
research, and investigates the causes, treatments, and cures for both common
and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.