Accuracy of ICD-9-CM codes in identifying reportable communicable diseases.

Billing records from the outpatient clinics of a university medical center were used to identify reportable communicable diseases. Patient charts were reviewed to check the accuracy of all cases of communicable diseases not reported to the local health department. Thirty-three percent of the cases identified as one of 20 communicable diseases, using the ICD-9-CM system, were found to be incorrectly coded. This study documents a lack of specificity (numerous false positives) when using encounter form data and ICD-9-CM codes to identify communicable diseases in an outpatient setting.