• Akerke Baibergenova, Lehana Thabane, Noori Akhtar-Danesh, Mitchell Levine, Amiram Gafni, Rahim Moineddin, and Indra Pulcins.
• Department of Clinical Epidemiology and Biostatistics, McMaster University, Faculty of Health Sciences, L8N 3Z5, Hamilton, ON, Canada. baibera@mcmaster.ca
• Eur. J. Epidemiol. 2005 Jan 1;20(11):947-56.

ObjectiveTo examine the pattern and strength of seasonal fluctuations in emergency department (ED) visits due to asthma, by month and day of the week, by the patient's age, gender, and severity of asthma attack.MethodsTime series analysis of ED visits was conducted among patients with asthma aged from 18 to 55 years who visited Ontario EDs between April 1, 2001 and March 31, 2004. Autoregressive regression models with months and days of the week as predictors were fitted for (1) all patients; (2) females and males separately; (3) each combination of gender and age group, and (4) each combination of gender and level of severity. The strength of seasonality in each group of patients was estimated from the R2-statistic derived from autoregression models.ResultsFor all patient groups, the highest number of ED visits occurred in October and December, and on Sundays and Mondays. Month of January and Fridays were associated with a decreased number of visits. The strength of seasonality was similar in men and women (R2 = 0.52), was the highest in young patients and decreased with age, in men more rapidly than in women. Severe cases of asthma attacks exhibited weaker seasonality (R2 = 0.30) compared to mild (R2 = 0.45) or moderate (R2 = 0.53) cases.ConclusionThe strength of seasonal patterns of asthma ED visits is influenced by age and the severity of attack, and to a lesser extent, gender. Understanding the significance of seasonal precipitants of asthma in different patients subgroups could lead to better management strategies.

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