Asthma morbidity and ambient air pollution: effect modification by residential traffic-related air pollution.
BACKGROUND
Ambient air pollution has been associated with asthma-related hospital admissions and emergency department visits (hospital encounters). We hypothesized that higher individual exposure to residential traffic-related air pollutants would enhance these associations.


METHODS
We studied 11,390 asthma-related hospital encounters among 7492 subjects 0-18 years of age living in Orange County, California. Ambient exposures were measured at regional air monitoring stations. Seasonal average traffic-related exposures (PM2.5, ultrafine particles, NOx, and CO) were estimated near subjects' geocoded residences for 6-month warm and cool seasonal periods, using dispersion models based on local traffic within 500 m radii. Associations were tested in case-crossover conditional logistic regression models adjusted for temperature and humidity. We assessed effect modification by seasonal residential traffic-related air pollution exposures above and below median dispersion-modeled exposures. Secondary analyses considered effect modification by traffic exposures within race/ethnicity and insurance group strata.


RESULTS
Asthma morbidity was positively associated with daily ambient O3 and PM2.5 in warm seasons and with CO, NOx, and PM2.5 in cool seasons. Associations with CO, NOx, and PM2.5 were stronger among subjects living at residences with above-median traffic-related exposures, especially in cool seasons. Secondary analyses showed no consistent differences in association, and 95% confidence intervals were wide, indicating a lack of precision for estimating these highly stratified associations.


CONCLUSIONS
Associations of asthma with ambient air pollution were enhanced among subjects living in homes with high traffic-related air pollution. This may be because of increased susceptibility (greater asthma severity) or increased vulnerability (meteorologic amplification of local vs. correlated ambient exposures).
From the aDepartment of Epidemiology, School of Medicine, University of California, Irvine, Irvine, CA; bProgram in Public Health, College of Health Sciences, University of California, Irvine, Irvine, CA; cDepartment of Statistics, School of Information and Computer Sciences, University of California, Irvine, Irvine, CA; and dDivision of Pulmonary Medicine, Children's Hospital of Orange County, Orange, CA.
Ralph J
RJ
Delfino
Jun
J
Wu
Thomas
T
Tjoa
Sevan K
SK
Gullesserian
Bruce
B
Nickerson
Daniel L
DL
Gillen
D000293:Adolescent; D000397:Air Pollution / Q000032:analysis / Q000706:statistics & numerical data*; D001249:Asthma / Q000453:epidemiology*; D002140:California / Q000453:epidemiology; D002248:Carbon Monoxide / Q000032:analysis; D002648:Child; D002675:Child, Preschool; D015987:Effect Modifier, Epidemiologic; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D004781:Environmental Exposure; D005260:Female; D062305:Geographic Mapping; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D008297:Male; D009589:Nitrogen Oxides / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis; D012307:Risk Factors; D001335:Vehicle Emissions / Q000032:analysis
D009589:Nitrogen Oxides; D052638:Particulate Matter; D001335:Vehicle Emissions; D002248:Carbon Monoxide