title: Myocardial infarction on snow days: incidence, procedure, use and outcomes.
abstract: BACKGROUND
  Snowfall can cause chaos in urban centres and put considerable stress on health care systems. Given that myocardial infarction (MI) is a condition that may be triggered or aggravated by stress, and that health system stress could influence the typical care provided to patients with MI, a study was conducted comparing 'snow days' with 'nonsnow days', specifically assessing the incidence of MI, the use of acute procedures and in-hospital mortality.
  
  
  METHODS
  Hospital discharge data were used on all patients discharged after MI. These data were merged with data from Environment Canada to determine the amount of snowfall that occurred on any given day. The use of acute procedures was determined by linking to data from the Alberta Provincial PRoject for Outcomes Assessment in Coronary Heart disease (APPROACH). Snow days were defined as days when at least 5 cm of snow fell, and the two subsequent days were included because of the lingering effect of 'urban chaos' that can ensue after significant snowfall. The average incidence of MIs on snow days versus nonsnow days was then determined. Risk-adjusted odds ratios for the use of direct percutaneous coronary intervention and in-hospital mortality were also determined.
  
  
  RESULTS
  There were 61 snow days and 575 nonsnow days. The incidence of MI (incidence density ratio of 1.08, 95% CI 0.82 to 3.10) and the use of direct percutaneous coronary intervention (adjusted OR=1.07, 95% CI 0.74 to 1.54) were slightly higher on snow days. In-hospital mortality trended toward being lower (adjusted OR=0.54, 95% CI 0.28 to 1.04) for patients admitted on snow days, although none of these differences were statistically significant.
  
  
  CONCLUSIONS
  Despite the potential for the significant adverse effects of snow days on the incidence of MI, the use of acute procedures and outcomes, these findings suggest only minor effects, if any.
authors.affiliation: Department of community Health Sciences, University of Calgary, Alberta.
authors.forename: Danielle A
authors.initials: DA
authors.lastname: Southern
authors.forename: Merril L
authors.initials: ML
authors.lastname: Knudtson
authors.forename: William A
authors.initials: WA
authors.lastname: Ghali
mesh_terms: D000368:Aged; D000416:Alberta / Q000453:epidemiology; D015906:Angioplasty, Balloon, Coronary / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D017052:Hospital Mortality / Q000639:trends; D006801:Humans; D015994:Incidence; D008297:Male; D009203:Myocardial Infarction / Q000453:epidemiology* / Q000209:etiology / Q000628:therapy; D016017:Odds Ratio; D012189:Retrospective Studies; D012914:Snow