title: Ambient ozone concentrations and the risk of perforated and nonperforated appendicitis: a multicity case-crossover study.
abstract: BACKGROUND
  Environmental determinants of appendicitis are poorly understood. Past work suggests that air pollution may increase the risk of appendicitis.
  
  
  OBJECTIVE
  We investigated whether ambient ground-level ozone (O3) concentrations were associated with appendicitis and whether these associations varied between perforated and nonperforated appendicitis.
  
  
  METHODS
  We based this time-stratified case-crossover study on 35,811 patients hospitalized with appendicitis from 2004 to 2008 in 12 Canadian cities. Data from a national network of fixed-site monitors were used to calculate daily maximum O3 concentrations for each city. Conditional logistic regression was used to estimate city-specific odds ratios (ORs) relative to an interquartile range (IQR) increase in O3 adjusted for temperature and relative humidity. A random-effects meta-analysis was used to derive a pooled risk estimate. Stratified analyses were used to estimate associations separately for perforated and nonperforated appendicitis.
  
  
  RESULTS
  Overall, a 16-ppb increase in the 7-day cumulative average daily maximum O3 concentration was associated with all appendicitis cases across the 12 cities (pooled OR = 1.07; 95% CI: 1.02, 1.13). The association was stronger among patients presenting with perforated appendicitis for the 7-day average (pooled OR = 1.22; 95% CI: 1.09, 1.36) when compared with the corresponding estimate for nonperforated appendicitis [7-day average (pooled OR = 1.02, 95% CI: 0.95, 1.09)]. Heterogeneity was not statistically significant across cities for either perforated or nonperforated appendicitis (p > 0.20).
  
  
  CONCLUSIONS
  Higher levels of ambient O3 exposure may increase the risk of perforated appendicitis.
authors.affiliation: Department of Medicine, Environmental Health Research Group, Institute of Public Health, University of Calgary, Calgary, Alberta, Canada. ggkaplan@ucalgary.ca
authors.forename: Gilaad G
authors.initials: GG
authors.lastname: Kaplan
authors.forename: Divine
authors.initials: D
authors.lastname: Tanyingoh
authors.forename: Elijah
authors.initials: E
authors.lastname: Dixon
authors.forename: Markey
authors.initials: M
authors.lastname: Johnson
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Wheeler
authors.forename: Robert P
authors.initials: RP
authors.lastname: Myers
authors.forename: Stefania
authors.initials: S
authors.lastname: Bertazzon
authors.forename: Vineet
authors.initials: V
authors.lastname: Saini
authors.forename: Karen
authors.initials: K
authors.lastname: Madsen
authors.forename: Subrata
authors.initials: S
authors.lastname: Ghosh
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Villeneuve
mesh_terms: D000328:Adult; D000393:Air Pollutants / Q000032:analysis / Q000633:toxicity*; D001064:Appendicitis / Q000139:chemically induced* / Q000145:classification / Q000453:epidemiology*; D002170:Canada / Q000453:epidemiology; D002947:Cities; D018592:Cross-Over Studies; D004781:Environmental Exposure; D004784:Environmental Monitoring; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D010126:Ozone / Q000032:analysis / Q000633:toxicity*; D012189:Retrospective Studies; D012621:Seasons; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D010126:Ozone