Seasonal modification of the association between temperature and adult emergency department visits for asthma: a case-crossover study
The objective of this study is to characterize the effect of temperature on emergency department visits for asthma and modification of this association by season. This association is of interest in its own right, and also important to understand because temperature may be an important confounder in analyses of associations between other environmental exposures and asthma. For example, the case-crossover study design is commonly used to investigate associations between air pollution and respiratory outcomes, such as asthma. This approach controls for confounding by month and season by design, and permits adjustment for potential confounding by temperature through regression modeling. However, such models may fail to adequately control for confounding if temperature effects are seasonal, since case-crossover analyses rarely account for interactions between matching factors (such as calendar month) and temperature.
We conducted a case-crossover study to determine whether the association between temperature and emergency department visits for asthma varies by season or month. Asthma emergency department visits among North Carolina adults during 2007–2008 were identified using a statewide surveillance system. Marginal as well as season- and month-specific associations between asthma visits and temperature were estimated with conditional logistic regression.
The association between temperature and adult emergency department visits for asthma is near null when the overall association is examined [odds ratio (OR) per 5 degrees Celsius = 1.01, 95% confidence interval (CI): 1.00, 1.02]. However, significant variation in temperature-asthma associations was observed by season (chi-square = 18.94, 3 degrees of freedom, p <0.001) and by month of the year (chi-square = 45.46, 11 degrees of freedom, p <0.001). ORs per 5 degrees Celsius were increased in February (OR = 1.06, 95% CI: 1.02, 1.10), July (OR = 1.16, 95% CI: 1.04, 1.29), and December (OR = 1.04, 95% CI: 1.01, 1.07) and decreased in September (OR = 0.92, 95% CI: 0.87, 0.97).
Our empirical example suggests that there is significant seasonal variation in temperature-asthma associations. Epidemiological studies rarely account for interactions between ambient temperature and temporal matching factors (such as month of year) in the case-crossover design. These findings suggest that greater attention should be given to seasonal modification of associations between temperature and respiratory outcomes in case-crossover analyses of other environmental asthma triggers.
- Janes H, Sheppard L, Lumley T: Case-crossover analyses of air pollution exposure data: referent selection strategies and their implications for bias. Epidemiology 2005, 16:717–726. CrossRef
- Mittleman MA: Optimal referent selection strategies in case-crossover studies: a settled issue. Epidemiology 2005, 16:715–716. CrossRef
- D’Ippoliti D, Forastiere F, Ancona C, Agabiti N, Fusco D, Michelozzi P, Perucci CA: Air pollution and myocardial infarction in Rome: a case-crossover analysis. Epidemiology 2003, 14:528–535. CrossRef
- Smargiassi A, Kosatsky T, Hicks J, Plante C, Armstrong B, Villeneuve PJ, Goudreau S: Risk of asthmatic episodes in children exposed to sulfur dioxide stack emissions from a refinery point source in Montreal, Canada. Environ Health Perspect 2009, 117:653–659.
- Stafoggia M, Schwartz J, Forastiere F, Perucci CA, Group S: Does temperature modify the association between air pollution and mortality? A multicity case-crossover analysis in Italy. Am J Epidemiol 2008, 167:1476–1485. CrossRef
- Zanobetti A, Schwartz J: Air pollution and emergency admissions in Boston, MA. J Epidemiol Community Health 2006, 60:890–895. CrossRef
- Levy D, Lumley T, Sheppard L, Kaufman J, Checkoway H: Referent selection in case-crossover analyses of acute health effects of air pollution. Epidemiology 2001, 12:186–192. CrossRef
- Abe T, Tokuda Y, Ohde S, Ishimatsu S, Nakamura T, Birrer RB: The relationship of short-term air pollution and weather to ED visits for asthma in Japan. Am J Emerg Med 2009, 27:153–159. CrossRef
- Chen CH, Xirasagar S, Lin HC: Seasonality in adult asthma admissions, air pollutant levels, and climate: a population-based study. J Asthma 2006, 43:287–292. CrossRef
- Garty BZ, Kosman E, Ganor E, Berger V, Garty L, Wietzen T, Waisman Y, Mimouni M, Waisel Y: Emergency room visits of asthmatic children, relation to air pollution, weather, and airborne allergens. Ann Allergy Asthma Immunol 1998, 81:563–570. CrossRef
- Gosai A, Salinger J, Dirks K: Climate and respiratory disease in Auckland, New Zealand. Aust N Z J Public Health 2009, 33:521–526. CrossRef
- Grech V, Balzan M, Asciak RP, Buhagiar A: Seasonal variations in hospital admissions for asthma in Malta. J Asthma 2002, 39:263–268. CrossRef
- Ivey MA, Simeon DT, Monteil MA: Climatic variables are associated with seasonal acute asthma admissions to accident and emergency room facilities in Trinidad, West Indies. Clin Exp Allergy 2003, 33:1526–1530. CrossRef
- Nastos PT, Paliatsos AG, Papadopoulos M, Bakoula C, Priftis KN: The effect of weather variability on pediatric asthma admissions in Athens, Greece. J Asthma 2008, 45:59–65. CrossRef
- Rossi OV, Kinnula VL, Tienari J, Huhti E: Association of severe asthma attacks with weather, pollen, and air pollutants. Thorax 1993, 48:244–248. CrossRef
- Chavarria JF: Short report: Asthma admissions and weather conditions in Costa Rica. Arch Dis Child 2001, 84:514–515. CrossRef
- Green RS, Basu R, Malig B, Broadwin R, Kim JJ, Ostro B: The effect of temperature on hospital admissions in nine California counties. Int J Public Health 2010, 55:113–121. CrossRef
- Khot A, Burn R, Evans N, Lenney W, Storr J: Biometeorological triggers in childhood asthma. Clin Allergy 1988, 18:351–358. CrossRef
- Priftis KN, Paliatsos AG, Panagiotopoulou-Gartagani P, Tapratzi-Potamianou P, Zachariadi-Xypolita A, Nicolaidou P, Saxoni-Papageorgiou P: Association of weather conditions with childhood admissions for wheezy bronchitis or asthma in Athens. Respiration 2006, 73:783–790. CrossRef
- Lin S, Luo M, Walker RJ, Liu X, Hwang SA, Chinery R: Extreme high temperatures and hospital admissions for respiratory and cardiovascular diseases. Epidemiology 2009, 20:738–746. CrossRef
- Villeneuve PJ, Leech J, Bourque D: Frequency of emergency room visits for childhood asthma in Ottawa, Canada: the role of weather. Int J Biometeorol 2005, 50:48–56. CrossRef
- Mohr LB, Luo S, Mathias E, Tobing R, Homan S, Sterling D: Influence of season and temperature on the relationship of elemental carbon air pollution to pediatric asthma emergency room visits. J Asthma 2008, 45:936–943. CrossRef
- Lu Y, Symons JM, Geyh AS, Zeger SL: An approach to checking case-crossover analyses based on equivalence with time-series methods. Epidemiology 2008, 19:169–175. CrossRef
- Schisterman EF, Cole SR, Platt RW: Overadjustment bias and unnecessary adjustment in epidemiologic studies. Epidemiology 2009, 20:488–495. CrossRef
- Kaufman JS, Maclehose RF, Kaufman S: A further critique of the analytic strategy of adjusting for covariates to identify biologic mediation. Epidemiol Perspect Innov 2004, 1:4. CrossRef
- Seasonal modification of the association between temperature and adult emergency department visits for asthma: a case-crossover study
- Open Access
- Available under Open Access This content is freely available online to anyone, anywhere at any time.
- Online Date
- August 2012
- Online ISSN
- BioMed Central
- Additional Links