Winter temperature inversions and emergency department visits for asthma in Salt Lake County, Utah, 2003-2008.
BACKGROUND
Winter temperature inversions-layers of air in which temperature increases with altitude-trap air pollutants and lead to higher pollutant concentrations. Previous studies have evaluated associations between pollutants and emergency department (ED) visits for asthma, but none have considered inversions as independent risk factors for ED visits for asthma.


OBJECTIVE
We aimed to assess associations between winter inversions and ED visits for asthma in Salt Lake County, Utah.


METHODS
We obtained electronic records of ED visits for asthma and data on inversions, weather, and air pollutants for Salt Lake County, Utah, during the winters of 2003 through 2004 to 2007 through 2008. We identified 3,425 ED visits using a primary diagnosis of asthma. We used a time-stratified case-crossover design, and conditional logistic regression models to calculate odds ratios (ORs) and 95% confidence intervals (CIs) to estimate rate ratios of ED visits for asthma in relation to inversions during a 4-day lag period and prolonged inversions. We evaluated interactions between inversions and weather and pollutants.


RESULTS
After adjusting for dew point and mean temperatures, the OR for ED visits for asthma associated with inversions 0-3 days before the visit compared with no inversions during the lag period was 1.14 (95% CI: 1.00, 1.30). The OR for each 1-day increase in the number of inversion days during the lag period was 1.03 (95% CI: 1.00, 1.07). Associations were only apparent when PM10 and maximum and mean temperatures were above median levels.


CONCLUSIONS
Our results provide evidence that winter inversions are associated with increased rates of ED visits for asthma.
Environmental Epidemiology Program, Utah Department of Health, Salt Lake City, Utah, USA. jdbeard@email.unc.edu
John D
JD
Beard
Celeste
C
Beck
Randall
R
Graham
Steven C
SC
Packham
Monica
M
Traphagan
Rebecca T
RT
Giles
John G
JG
Morgan
D000293:Adolescent; D000328:Adult; D000393:Air Pollutants / Q000032:analysis / Q000633:toxicity*; D001249:Asthma / Q000453:epidemiology* / Q000209:etiology; D002648:Child; D002675:Child, Preschool; D018592:Cross-Over Studies; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D005260:Female; D006358:Hot Temperature; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D016017:Odds Ratio; D012621:Seasons; D014589:Utah / Q000453:epidemiology; D014887:Weather; D055815:Young Adult
D000393:Air Pollutants