title: Importance of ICD-10 coding directive change for acute gastroenteritis (unspecified) for rotavirus vaccine impact studies: illustration from a population-based cohort study from Ontario, Canada.
abstract: BACKGROUND
  In Ontario, Canada, we conducted an evaluation of rotavirus (RV) vaccine on hospitalizations and Emergency Department (ED) visitations for acute gastroenteritis (AGE). In our original analysis, any one of the International Classification of Disease, Version 10 (ICD-10) codes was used for outcome ascertainment: RV-specific- (A08.0), viral- (A08.3, A08. 4, A08.5), and unspecified infectious- gastroenteritis (A09). Annual age-specific rates per 10,000 population were calculated.
  
  
  RESULTS
  The average monthly rate of AGE hospitalization for children under age two increased from 0.82 per 10,000 from January 2003 to March 2009, to 2.35 over the period of April 2009 to March 31, 2013. Similar trends were found for ED consultations and in other age groups. A rise in events corresponding to the A09 code was found when the outcome definition was disaggregated by ICD-10 code. Documentation obtained from the World Health Organization confirmed that a change in directive for the classification of unspecified gastroenteritis occurred with the release of ICD-10 in April 2009. AGE events previously classified under the code K52.9, are now classified under code A09.9.
  
  
  CONCLUSIONS
  Based on change in the classification of unspecified gastroenteritis we modified our outcome definition to also include unspecified non-infectious-gastroenteritis (K52.9). We recommend other investigators consider using both A09.9 and K52.9 ICD-10 codes for outcome ascertainment in future rotavirus vaccine impact studies to ensure that all unspecified cases of AGE are captured, especially if the study period spans 2009.
authors.affiliation: Public Health Ontario, 480 University Avenue, Suite 300, Toronto, ON, M5G 1V2, Canada. sarah.wilson@oahpp.ca.|Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada. sarah.wilson@oahpp.ca.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Wilson
authors.affiliation: Public Health Ontario, 480 University Avenue, Suite 300, Toronto, ON, M5G 1V2, Canada. shelley.deeks@oahpp.ca.|Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada. shelley.deeks@oahpp.ca.
authors.forename: Shelley L
authors.initials: SL
authors.lastname: Deeks
authors.affiliation: Public Health Ontario, 480 University Avenue, Suite 300, Toronto, ON, M5G 1V2, Canada. laura.rosella@utoronto.ca.|Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada. laura.rosella@utoronto.ca.|Institute for Clinical Evaluative Sciences, Toronto, ON, Canada. laura.rosella@utoronto.ca.
authors.forename: Laura C
authors.initials: LC
authors.lastname: Rosella
mesh_terms: D000208:Acute Disease; D002675:Child, Preschool; D015331:Cohort Studies; D005759:Gastroenteritis / Q000175:diagnosis* / Q000276:immunology*; D006760:Hospitalization; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D038801:International Classification of Diseases; D009864:Ontario; D022243:Rotavirus Vaccines / Q000276:immunology*; D012621:Seasons; D013997:Time Factors
chemical_list: D022243:Rotavirus Vaccines