Higher exposure to traffic-related air pollution dramatically increases the odds of readmission to the hospital for asthma – but only for white children, according to a new study from Cincinnati Children’s.

The study shows that white children exposed to high levels of traffic-related air pollution (TRAP) are three times more likely to be readmitted for asthma than white children with low exposure. However, traffic pollution did not increase the risk for black children despite their having overall higher rates of asthma readmission than white children.

Detailed findings were published online March 27, 2014, in The Journal of Pediatrics.

“Although black children in our study had a higher rate of asthma readmission overall, TRAP exposure was not a discernible factor for these children. This suggests that other factors such as social stress or other environmental factors may be particularly relevant in this population,” says Nicholas Newman, DO, a pediatrician at Cincinnati Children’s and lead author of the study.

“For example, caregivers of black children reported significantly higher rates of psychological distress and were more likely to live in poorer housing conditions, with visible cockroaches or holes or cracks in the walls. These other factors may mask or overwhelm the impact of TRAP in black children.”

The researchers studied 758 children, ages 1 to 16, who were admitted to Cincinnati Children’s for asthma or wheezing. Fifty-eight percent were black and 32 percent white. Nineteen percent of all children were readmitted within the 12-month period.

Traffic-related pollution is a complex mixture of chemicals and particles including a significant amount of diesel particulate matter. The tiny size of diesel particles makes them more likely to be inhaled into the lungs where they can cause swelling that blocks airways.

Pollution exposure was estimated using a previously developed model that sampled ambient air at 27 sites in the Cincinnati area between 2001 and 2006. This model was used to estimate exposure for children enrolled in the study based on their home address.

The study is the most recent to be published as part of the Greater Cincinnati Asthma Risks Study (GCARS), which seeks to understand the causes of hospital readmission, particularly for low-income and minority children.

“This study adds to the evidence that TRAP exposure worsens the health of children with asthma,” says Robert Kahn MD, MPH, Associate Director of General and Community Pediatrics at Cincinnati Children’s and senior author of the study. “We hope that this study can inform public policy. It may also suggest ways to personalize patient care based on environmental risks.”