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
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