Asthma - children at risk

Children who are exposed to high levels of traffic-related pollution and high levels of indoor endotoxin early in life have six times the risk of developing persistent wheezing by age three than children exposed to low levels of traffic and indoor-related pollutants, according to new research from the University of Cincinnati College of Medicine.

The research also suggests a synergistic effect between outdoor traffic-related pollution and indoor endotoxin, a component of certain bacteria, which appear to cause more harm to developing lungs together than would be predicted by the effect of either exposure alone.

The study was published in the December 1, 2009, edition of the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.

"There is a clear synergistic effect from co-exposure to traffic-related particles and endotoxin above and beyond what you would see with a single exposure that can be connected to persistent wheezing by age three," explained lead author Patrick Ryan, Ph.D., a research assistant professor of environmental health at the University of Cincinnati. "These two exposure sources—when simultaneously present at high levels—appear to work together to negatively impact the health of young children with developing lungs."

Endotoxin exposure alone appeared to have little effect

This is believed to be the first study to examine the combined effects of endotoxin and traffic-related particle exposures in a birth cohort.

In the study, 624 children at high risk for developing allergic disease— with at least one atopic parent—were enrolled and completed a clinical examination, exposure and symptoms questionnaires and skin prick tests for allergy at years one, two and three. The researchers used land-use regression modelling to calculate study participants' exposures to traffic-related particles, such as diesel exhaust and home visits to sample the levels of indoor endotoxin exposure.

Of the children studied who were exposed to high levels of both traffic-related pollution and indoor endotoxin, more than a third— 36%— demonstrated persistent wheezing at age three, an early warning sign of asthma and other pulmonary conditions. In contrast, in children exposed to low levels of both indoor and outdoor allergens, only 11% experienced wheezing. Among children exposed to low levels of indoor endotoxin but high levels of traffic-related particles, 18% demonstrated persistent wheezing, but endotoxin exposure alone appeared to have little effect.

Greater impact

"Traffic-related particles and endotoxin both seem to trigger an inflammatory response in the children monitored in this study. When put together, that effect is amplified to have a greater impact on the body's response," added Dr. Ryan. "The earlier in life this type of exposure occurs, the more impact it may have long term. Lung development occurs in children up through age 18 or 20. Exposure earlier in life to both endotoxin and traffic will have a greater impact on developing lungs compared to adults whose lungs are already developed."

www.thoracic.org/sections/publications/press-releases/resources/endotoxin_ed.pdf