Exposure to household
endotoxin levels poses a significant risk for asthma,
according to the first nationwide sampling of house dust.
The study appears in the first
issue for December 2005 of the American Journal of Respiratory
and Critical Care Medicine, published by the American
Endotoxins are toxic substances
associated with the outer membrane of certain gram-negative
bacteria. These molecules are bound to the bacterial cell
wall and are released when the bacterium ruptures or disintegrates.
According to the authors, inhalation exposure to endotoxins
is common in homes. Indoor sources include: dust, pets,
humidifiers, pests, and outdoor air.
Past studies have shown that exposure
can cause lung inflammation.
Peter S. Thorne, Ph.D., of the Environmental
Health Sciences Research Center at the University of Iowa,
Iowa City, and five associates, evaluated 2,456 residents
in 831 homes selected to represent the demographic characteristics
of the U.S. population. The investigators took 2,552 house
dust samples from five locations within the homes, including
bedroom floors, bedding, family room floors, sofa surfaces,
and kitchen floors.
"This study clearly demonstrates
significant relationships between household endotoxin
and diagnosed asthma, recent asthma symptoms, current
use of asthma medications, and wheezing," said Dr.
Thorne. "No effect was observed of allergy status
on the relationship between endotoxin and asthma outcomes.
This suggests that current endotoxin exposure may have
little impact on allergy status and that airway inflammation
is the most significant effect of endotoxin exposure in
a cross-section of the population."
The authors found the strongest
relationship between asthma, asthma medications, and wheezing
came from endotoxin levels in bedroom floor and bedding
dust. However, the effects were observed only in adults
and not in children.
Moreover, the investigators also
noted that the endotoxin concentrations were highest in
kitchen and living room floor dust, and lowest for bedding
(including mattress and pillow).
"The mean concentration of
endotoxin in the kitchen floor dust was 2.3-fold higher
than bedroom floor dust and 4.3-fold higher than bedding
dust," said Dr. Thorne.
Two field workers visited each household
and took answers from residents to detailed questionnaires,
conducted a home inspection, and vacuumed dust into an
The study yielded an 11.3 percent
prevalence rate for diagnosed asthma among the homes surveyed.
This figure compared favorably with the 11.1 percent prevalence
rate of diagnosed asthma associated with the 2002 National
Health Interview Survey.
The authors also noted that their
national survey demonstrated that U.S. household endotoxin
exposure levels were higher than those in Europe.