title: Air pollution and daily emergency department visits for headache in Montreal, Canada.
abstract: BACKGROUND
  Many studies have indicated that weather can trigger headache. Here we propose a new methodological approach to assess the relationship between weather, ambient air pollution, and emergency department (ED) visits for this condition.
  
  
  OBJECTIVE
  To examine the associations between ED visits for headache and selected meteorological and air pollution factors.
  
  
  METHODS
  A hierarchical clusters design was used to study 10,497 ED visits for headache (ICD-9: 784) that occurred at a Montreal hospital between 1997 and 2002. The generalized linear mixed models technique was applied to create Poisson models for the clustered counts of visits for headache.
  
  
  RESULTS
  Statistically significant positive associations were observed between the number of ED visits for headache and the atmospheric pressure for all and for female visits for 1-day and 2-day lagged exposures. The percentage increase in daily ED female visits was 4.1% (95% CI: 2.0, 6.2), 3.4% (95% CI: 1.4, 5.6), and 2.2% (95% CI: 1.4, 5.6) for current day, 1-day and 2-day lagged exposure to SO(2), respectively, for an increase of an interquartile range (IQR) of 2.4 ppb. The percentage increase was also statistically significant for current day and 1-day lagged exposure to NO(2) and CO for all and for female visits.
  
  
  CONCLUSIONS
  Presented findings provide support for the hypothesis that ED visits for headache are correlated to weather conditions and ambient air pollution - to atmospheric pressure and exposure to SO(2), NO(2), CO, and PM(2.5). An increase in levels of these factors is associated with an increase in the number of ED visits for headache.
authors.affiliation: Air Health Effects Division, Health Canada, Ottawa, Ontario, Canada.
authors.forename: Mieczyslaw
authors.initials: M
authors.lastname: Szyszkowicz
mesh_terms: D000393:Air Pollutants / Q000009:adverse effects; D000397:Air Pollution / Q000009:adverse effects* / Q000706:statistics & numerical data*; D001274:Atmospheric Pressure; D002170:Canada; D002248:Carbon Monoxide / Q000009:adverse effects; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D005260:Female; D006261:Headache / Q000209:etiology*; D006801:Humans; D016014:Linear Models; D008297:Male; D009585:Nitrogen Dioxide / Q000009:adverse effects
chemical_list: D000393:Air Pollutants; D002248:Carbon Monoxide; D009585:Nitrogen Dioxide