Is it traffic type, volume, or distance? Wheezing in infants living near truck and bus traffic.

BACKGROUND: Previous studies of air pollution have not examined the association between exposure to varying types, distance, and amounts of traffic and wheezing in very young infants. OBJECTIVE: We sought to determine the relationship between types of traffic, traffic volume, and distance and wheezing among infants less than 1 year of age. METHODS: A geographic information system and a classification scheme were developed to categorize infants enrolled in the study as living near moving truck and bus traffic (highway >50 miles per hour, >1000 trucks daily, <400 m), stop-and-go truck and bus traffic (<50 miles per hour, <100 m), or unexposed and not residing near either. Symptom data were based on health questionnaires administered to parents when the infants were 6 months of age and monthly health diaries. RESULTS: Infants living very near (<100 m) stop-and-go bus and truck traffic had a significantly increased prevalence of wheezing (adjusted odds ratio, 2.50; 95% CI, 1.15-5.42) when compared with unexposed infants. The prevalence of wheezing among nonwhite infants was at least twice that of white infants, regardless of exposure. Infants living less than 400 m from a high volume of moving traffic, however, did not have an increased prevalence of wheezing. CONCLUSION: These results suggest that the distance from and type of traffic exposures are more significant risk factors than traffic volume for wheezing in early infancy.