title: Classification of emergency department chief complaints into 7 syndromes: a retrospective analysis of 527,228 patients.
abstract: OBJECTIVE
  Electronic surveillance systems often monitor triage chief complaints in hopes of detecting an outbreak earlier than can be accomplished with traditional reporting methods. We measured the accuracy of a Bayesian chief complaint classifier called CoCo that assigns patients 1 of 7 syndromic categories (respiratory, botulinic, gastrointestinal, neurologic, rash, constitutional, or hemorrhagic) based on free-text triage chief complaints.
  
  
  METHODS
  We compared CoCo's classifications with criterion syndromic classification based on International Classification of Diseases, Ninth Revision (ICD-9) discharge diagnoses. We assigned the criterion classification to a patient based on whether the patient's primary diagnosis was a member of a set of ICD-9 codes associated with CoCo's 7 syndromes. We tested CoCo's performance on a set of 527,228 chief complaints from patients registered at the University of Pittsburgh Medical Center emergency department (ED) between 1990 and 2003. We performed a sensitivity analysis by varying the ICD-9 codes in the criterion standard. We also tested CoCo on chief complaints from EDs in a second location (Utah).
  
  
  RESULTS
  Approximately 16% (85,569/527,228) of the patients were classified according to the criterion standard into 1 of the 7 syndromes. CoCo's classification performance (number of cases by criterion standard, sensitivity [95% confidence interval (CI)], and specificity [95% CI]) was respiratory (34,916, 63.1 [62.6 to 63.6], 94.3 [94.3 to 94.4]); botulinic (1,961, 30.1 [28.2 to 32.2], 99.3 [99.3 to 99.3]); gastrointestinal (20,431, 69.0 [68.4 to 69.6], 95.6 [95.6 to 95.7]); neurologic (7,393, 67.6 [66.6 to 68.7], 92.7 [92.6 to 92.8]); rash (2,232, 46.8 [44.8 to 48.9], 99.3 [99.3 to 99.3]); constitutional (10,603, 45.8 [44.9 to 46.8], 96.6 [96.6 to 96.7]); and hemorrhagic (8,033, 75.2 [74.3 to 76.2], 98.5 [98.4 to 98.5]). The sensitivity analysis showed that the results were not affected by the choice of ICD-9 codes in the criterion standard. Classification accuracy did not differ on chief complaints from the second location.
  
  
  CONCLUSIONS
  Our results suggest that, for most syndromes, our chief complaint classification system can identify about half of the patients with relevant syndromic presentations, with specificities higher than 90% and positive predictive values ranging from 12% to 44%.
authors.affiliation: Center for Biomedical Informatics, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA. chapman@cbmi.pitt.edu
authors.forename: Wendy W
authors.initials: WW
authors.lastname: Chapman
authors.forename: John N
authors.initials: JN
authors.lastname: Dowling
authors.forename: Michael M
authors.initials: MM
authors.lastname: Wagner
mesh_terms: D001499:Bayes Theorem; D002965:Classification / Q000379:methods*; D004636:Emergency Service, Hospital / Q000458:organization & administration* / Q000706:statistics & numerical data; D006801:Humans; D038801:International Classification of Diseases; D010414:Pennsylvania; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D009626:Terminology as Topic; D014218:Triage / Q000379:methods*