Are Frequent Asthma Symptoms Among Low-Income Individuals Related to Heavy Traffic Near Homes, Vulnerabilities, or Both?

Purpose To investigate whether frequent asthma symptoms (daily/weekly symptoms) can be attributed to traffic-related exposures, poverty, and/or vulnerabilities. Methods Annual average daily vehicle traffic density (TD) within 500 feet of 2001 California Health Interview Survey respondentsʹ residential cross streets was calculated. Logistic regression analyses were performed to evaluate the association between annual average TD and frequent asthma symptoms with income as a confounder and a modifier. Results After adjustment for age, sex, and race/ethnicity, a 92% increase in frequent asthma symptoms was observed among those in high TD and a 50% increase among those in medium TD compared to those in low TD. Adjustment for poverty did not change these estimates, but individuals in poverty were twice more likely to experience frequent symptoms. Furthermore, delays in care, a poor/fair health status, current/previous smoking, overweight/obese, or unemployment showed independent associations with frequent asthma symptoms. Analyses stratified on income indicated greater estimated traffic effects for asthmatics in poverty, whereas the estimates for asthmatics above the poverty level moved closer toward the null. Conclusions Traffic-related exposures, poverty and vulnerabilities all increased the risk of frequent asthma symptoms. Those in poverty appeared to be more strongly affected by heavy traffic near their residences.