Academic journal article Environmental Health Perspectives

Winter Temperature Inversions and Emergency Department Visits for Asthma in Salt Lake County, Utah, 2003-2008

Academic journal article Environmental Health Perspectives

Winter Temperature Inversions and Emergency Department Visits for Asthma in Salt Lake County, Utah, 2003-2008

Article excerpt

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.

KEY WORDS: asthma, case-crossover, emergency department, interaction, inversion, winter. Environ Health Perspect 120:1385-1390 (2012). http://dx.doi.org/10.1289/ehp.1104349 [Online 11 July 2012]

Weather patterns and topographical features in Salt Lake County, Utah, are optimal for the formation of winter temperature inversions (hereafter referred to as inversions) (Gillies et al. 2010), which occur when cold air becomes trapped at the earth's surface beneath a layer of warmer air above the surface. Bailey et al. (2011) estimated that Salt Lake City experienced daytime inversions on 57% of winter days from 1994 through 2008, although the number of inversion days varied greatly from year to year. Inversions can result in stagnant air masses and in the accumulation of air pollutants (Wallace and Kanaroglou 2009; Wallace et al. 2010), primarily particulate matter (Gillies et al. 2010; Monn et al. 1995; Silva et al. 2007; Tran and Molders 2011) that can exceed health-based National Ambient Air Quality Standards (NAAQS) [U.S. Environmental Protection Agency (EPA) 2009b]. Salt Lake County, which covers 742 square miles and is located in a valley surrounded by mountains, is home to an estimated 1.03 million people (U.S. Census Bureau 2011) who may be involuntarily exposed to inversions and associated build-up of air pollutants.

Several studies have evaluated associations between air pollutants and adverse respiratory symptoms, including nonadmitting emergency department (ED) visits, among asthmatics (U.S. EPA 2006, 2009a).

Abdul-Wahab et al. (2005) conducted an ecologic study of < 2,500 ED visits for diseases associated with air pollution (in aggregate) that occurred during a 1-year period in Oman. They found an association between the monthly number of inversion days and the monthly mean daily number of ED visits. Wallace et al. (2010) found a cross-sectional association between inversions and airway inflammation, which was measured by sputum cell counts, among 674 persons with asthma who resided in Hamilton, Ontario, Canada, but they found no associations with individual pollutants. Previous studies have not considered inversions or days on which inversions occurred as independent variables contributing to rates of ED visits for asthma. …

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