Utility of International Classification of Diseases, Ninth Revision, Clinical Modification Codes for Communicable Disease Surveillance

International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes have been proposed as a method of public health surveillance and are widely used in public health and clinical research. However, ICD-9-CM codes have been found to have variable accuracy for both health-care billing and disease classification, and they have never been comprehensively validated for use in public health surveillance. Therefore, the authors undertook a comprehensive analysis of the positive predictive values (PPVs) of ICD-9-CM codes for communicable diseases in 6 North Carolina health-care systems for the year 2003. Stratified random samples of patient charts with ICD-9-CM diagnoses for communicable diseases were reviewed and evaluated for their concordance with the Centers for Disease Control and Prevention surveillance case definitions. Semi-Bayesian hierarchical regression techniques were employed on the ensemble of disease-specific PPVs in order to reduce the overall mean squared error. The authors found that for the majority for diseases with higher incidence and straightforward laboratory-based diagnoses, the PPVs were high (>80%), with the important exception of tuberculosis, which had a PPV of 28.6% (95% uncertainty interval: 15.6, 46.5).