Accuracy of ICD-9-CM codes in identifying infections of pneumonia and herpes simplex virus in administrative data.

Purpose: Clinical epidemiology studies increasingly rely on electronic medical records data. The validity of International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis codes is crucial as they are often used to identify conditions of interest. We evaluated the use of archived ICD-9-CM codes to identify two representative infection-related conditions, pneumonia and herpes simplex virus (HSV), in a defined health system.

Methods: Records were obtained for a sample of 175 and 179 patients with ICD-9-CM codes for pneumonia and HSV, respectively. An adjudicated case status was assigned for each subject.

Results: The presence of a single ICD-9-CM code had a positive predictive value of 88% for pneumonia and 86% for HSV. False positives (noncases) accounted for less than 10% of records evaluated for each condition.

Conclusions: Our study demonstrates that ICD-9-CM codes for pneumonia and HSV were valid markers of a true history of these conditions, suggesting that ICD-9-CM codes can be used to successfully identify infection-related conditions in epidemiologic studies. However, validation studies for individual conditions may help identify condition-specific strategies to improve the performance of diagnostic codes.