• Daily asthma symptom score
  

• Unscheduled physician visits (including ER)
  
• Oral-cortico-steroid use
  

Between 1990- and 2003, we identified in Ontario, and subsequently across Canada, a striking increase in hospital admissions for asthma in children occurring predictably in the third week of September every year.1 In 2000 we undertook a retrospective case-control study comparing the clinical characteristics of children using local emergency rooms for asthma in September, with those of children presenting during the non-epidemic months of July-August. Based on that pilot study of 169 children, we developed a larger prospective case-control study of clinical and biological characteristics of children recruited as they presented to an emergency room for asthma during September 2001. The control group for this study were children recruited from the community who had symptomatic asthma but did not have a September exacerbation requiring emergency room utilization. We identified the presence of rhinovirus in the majority of children attending an ER with acute asthma, and also found rhinovirus in a substantial proportion of the community based controls. We also found a highly significant difference in use of medications for asthma, with the ER cases being much less likely to be receiving adequate anti-inflammatory medication. In September 2004 we conducted a pilot randomized controlled blinded clinical trial of the efficacy of montelukast in reducing morbidity caused by asthma exacerbations associated with respiratory viral infections (RVI) in children aged 2 to 14. We found a highly significant reduction in reported symptom free days in the montelukast group. The current study is a randomized placebo-controlled trial of montelukast, during September 2005 to confirm the results of our pilot study and to examine the effectiveness of montelukast in reducing asthma morbidity during RVIs in different age and sex groups with a range of risk of exacerbations. We also wish to compare the effectiveness of montelukast to placebo in reducing asthma morbidity during RVIs between groups of children concurrently taking no or other classes of asthma control medications.