title: Air pollution and emergency department visits for conjunctivitis: A case-crossover study.
abstract: OBJECTIVE
  The purpose of this study was to examine the associations between emergency department (ED) visits for conjunctivitis and ambient air pollution levels in urban regions across the province of Ontario, Canada.
  
  
  METHODS
  Information from the National Ambulatory Care Reporting System was used to create time-series records, for the period of April 2004 to December 2011, on emergency department visits of patients suffering from conjunctivitis. A total of 77 439 emergency department visits for conjunctivitis were analyzed. A time-stratified case-crossover design was applied, completed with meta-analysis in order to pool inter-city results. Odds ratio (OR) for an emergency department visit was calculated in different population strata per one-unit increase (one interquartile range - IQR increase in a pollutant's daily level) while controlling for the impacts of temperature and relative humidity.
  
  
  RESULTS
  Statistically significant positive results were observed in the female population sample, for nitrogen dioxide (NO2) exposure lagged 5-8 days, with the highest result for the 7-day lag (OR = 1.035, 95% CI: 1.018-1.052) and for fine particulate matter with a median aerodynamic diameter of less than 2.5 μm (PM2.5), for lags 6 and 7 days, with the highest result for lag 7 (OR = 1.017, 95% CI: 1.003-1.031). In the male population sample, statistically significant positive results were observed for NO2; at lag 5 days (OR = 1.024, 95% CI: 1.004-1.045) and for ozone (O3), at lags 0-3 and 7 days, with the highest result for lag 0 (OR = 1.038, 95% CI: 1.012-1.056). Also for males, statistically significant results were observed in the case of PM2.5 exposure lagged by 5 days (OR = 1.003, 95% CI: 1.000-1.038) and sulfur dioxide (SO2) exposure lagged by 1 and 2 days (OR = 1.016, 95% CI: 1.000-1.031 and OR = 1.018, 95% CI: 1.002-1.033).
  
  
  CONCLUSIONS
  The findings of this study suggest that there are associations between levels of air pollution and ED visits for conjunctivitis, with different temporal trends and strength of association by age, sex, and season.
authors.affiliation: Health Canada, Ottawa, Canada (Population Studies Division). mietek.szyszkowicz@canada.ca.
authors.forename: Mieczysław
authors.initials: M
authors.lastname: Szyszkowicz
authors.affiliation: University of Ottawa, Ottawa, Canada (Department of Mathematics and Statistics). termeh.kousha@hc-sc.gc.ca.
authors.forename: Termeh
authors.initials: T
authors.lastname: Kousha
authors.affiliation: University at Buffalo, Buffalo, United States of America (School of Nursing). jcastner@buffalo.edu.
authors.forename: Jessica
authors.initials: J
authors.lastname: Castner
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000706:statistics & numerical data*; D002648:Child; D002675:Child, Preschool; D002947:Cities / Q000453:epidemiology; D003231:Conjunctivitis / Q000175:diagnosis / Q000453:epidemiology*; D018592:Cross-Over Studies; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D009585:Nitrogen Dioxide / Q000032:analysis; D009864:Ontario / Q000453:epidemiology; D010126:Ozone / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis; D013458:Sulfur Dioxide / Q000032:analysis; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D013458:Sulfur Dioxide; D010126:Ozone; D009585:Nitrogen Dioxide
keywords: air pollution; case-crossover; conjunctivitis; emergency department visit; exposure; multi-city study