Study 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 (Cl)], and specificity [95% Cl]) 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. Conclusion: 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%.
