Abstract
BackgroundEpidemiologic studies of skin and soft tissue infections (SSTIs) depend upon accurate case identification. Our objective was to evaluate the positive predictive value (PPV) of electronic medical record data for identification of SSTIs in a primary care setting.MethodsA validation study was conducted among primary care outpatients in an academic healthcare system. Encounters during four non-consecutive months in 2010 were included if any of the following were present in the electronic health record: International Classification of Diseases, Ninth Revision (ICD-9) code for an SSTI, Current Procedural Terminology (CPT) code for incision and drainage, or a positive wound culture. Detailed chart review was performed to establish presence and type of SSTI. PPVs and 95% confidence intervals (CI) were calculated among all encounters, initial encounters, and cellulitis/abscess cases.ResultsOf the 731 encounters included, 514 (70.3%) were initial encounters and 448 (61.3%) were cellulitis/abscess cases. When the presence of an ICD-9 code, CPT code, or positive culture was used to identify SSTIs, 617 encounters were true positives, yielding a PPV of 84.4% [95% CI: 81.8–87.0%]. The PPV for using ICD-9 codes alone to identify SSTIs was 90.7% [95 % CI: 88.5–92.9%]. For encounters with cellulitis/abscess codes, the PPV was 91.5% [95% CI: 88.9–94.1%].ConclusionsICD-9 codes may be used to retrospectively identify SSTIs with a high PPV. Broadening SSTI case identification with microbiology data and CPT codes attenuates the PPV. Further work is needed to estimate the sensitivity of this method.
Highlights
Epidemiologic studies of skin and soft tissue infections (SSTIs) depend upon accurate case identification
Patient encounters were included if any of the following criteria were present in the electronic health records (EHR): an SSTI International classification of diseases- Ninth Revision (ICD-9) diagnosis code [erysipelas: 035; carbuncle and furuncle: 680.x; cellulitis and abscess: 681.0, 681.00, 681.01, 681.10, 681.9, 682.x; acute lymphadenitis: 683.x; impetigo: 684.x; other local infections of skin and subcutaneous tissue: 686.x; other specified diseases of hair and hair follicles: 704.8], Current Procedural Terminology (CPT) code for incision and drainage (IND) [10060/1, 10080/1, 10120/1, 10140, 10160, 10180], or a positive wound or tissue microbiology culture
54.4% were for female patients and the mean patient age was 39.1 years; 70.3% of the encounters were the initial visit for diagnosis and treatment of the SSTI (Table 2)
Summary
Epidemiologic studies of skin and soft tissue infections (SSTIs) depend upon accurate case identification. ICD-9 diagnosis codes have been more commonly used for retrospective identification and classification of SSTIs from administrative and electronic health records (EHR).[1,2,3,4,5,6] this is a simple and straightforward method for case identification, these data are not collected for research purposes and may be subject to misclassification. Since valid methods of case ascertainment are critical to minimize the effects of misclassification in epidemiologic and outcomes studies of SSTIs, our primary objectives in this study were to (1) estimate the PPV of ICD-9 diagnosis codes for the retrospective identification of SSTIs in an outpatient primary care setting and (2) determine whether modifying the SSTI identification algorithm to include additional diagnostic indicators (i.e., wound culture and incision and drainage) would improve the precision of prediction results
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