How Well Do Discharge Diagnoses Identify Hospitalised Patients with Community-Acquired Infections? – A Validation Study Daniel Pilsgaard Henriksen 1 *, Stig Lønberg Nielsen 2 , Christian Borbjerg Laursen 3 , Jesper Hallas 4 , Court Pedersen 2 , Annmarie Touborg Lassen 1 1 Department of Emergency Medicine, Odense University Hospital, Odense, Denmark, 2 Department of Infectious Diseases, Odense University Hospital, Odense, Denmark, 3 Department of Respiratory Medicine, Odense University Hospital, Odense, Denmark, 4 Department of Clinical Pharmacology, University of Southern Denmark, Odense, Denmark Abstract Background: Credible measures of disease incidence, trends and mortality can be obtained through surveillance using manual chart review, but this is both time-consuming and expensive. ICD-10 discharge diagnoses are used as surrogate markers of infection, but knowledge on the validity of infections in general is sparse. The aim of the study was to determine how well ICD-10 discharge diagnoses identify patients with community-acquired infections in a medical emergency department (ED), overall and related to sites of infection and patient characteristics. Methods: We manually reviewed 5977 patients admitted to a medical ED in a one-year period (September 2010-August 2011), to establish if they were hospitalised with community-acquired infection. Using the manual review as gold standard, we calculated the sensitivity, specificity, predictive values, and likelihood ratios of discharge diagnoses indicating infection. Results: Two thousand five hundred eleven patients were identified with community-acquired infection according to chart review (42.0%, 95% confidence interval [95%CI]: 40.8–43.3%) compared to 2550 patients identified by ICD-10 diagnoses (42.8%, 95%CI: 41.6–44.1%). Sensitivity of the ICD-10 diagnoses was 79.9% (95%CI: 78.1–81.3%), specificity 83.9% (95%CI: 82.6–85.1%), positive likelihood ratio 4.95 (95%CI: 4.58–5.36) and negative likelihood ratio 0.24 (95%CI: 0.22–0.26). The two most common sites of infection, the lower respiratory tract and urinary tract, had positive likelihood ratios of 8.3 (95%CI: 7.5–9.2) and 11.3 (95%CI: 10.2–12.9) respectively. We identified significant variation in diagnostic validity related to age, comorbidity and disease severity. Conclusion: ICD-10 discharge diagnoses identify specific sites of infection with a high degree of validity, but only a moderate degree when identifying infections in general. Citation: Henriksen DP, Nielsen SL, Laursen CB, Hallas J, Pedersen C, et al. (2014) How Well Do Discharge Diagnoses Identify Hospitalised Patients with Community-Acquired Infections? – A Validation Study. PLoS ONE 9(3): e92891. doi:10.1371/journal.pone.0092891 Editor: Felipe Dal Pizzol, Universidade do Extremo Sul Catarinense, Brazil Received November 27, 2013; Accepted February 26, 2014; Published March 24, 2014 Copyright: ß 2014 Henriksen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The study was funded as a part of the corresponding authors PhD study: A stipend for PhD students from the Faculty of Health Sciences, Odense University Hospital, as well as a stipend from the Research Foundation of Odense University Hospital, University of Southern Denmark and an unrestricted grant from the private philanthropic fund TrygFonden given to the University of Southern Denmark. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: In 2010 Dr. Laursen had travel expenses, hotel accommodations and course/conference fees for a meeting for future respiratory specialists covered by AstraZeneca. ATL was supported by an unrestricted grant from the private philanthropic fund TrygFonden given to the University of Southern Denmark. DPH, JH, SLN and CP declare no conflicts of interest. This does not alter the authors’ adherence to PLOS ONE policies on sharing data and materials. DPH, JH, SLN and CP declare no conflicts of interest. * E-mail: dphenriksen@health.sdu.dk Introduction Credible measures of disease incidence, trends and mortality are critical for a proper public healthcare management. This information can be obtained through surveillance using manual chart review, but this is both time-consuming and expensive [1]. Surveillance of infections often depends on notifications from the physicians. However, because patients are registered with diagnose codes at their discharge or transfer from department to department, it is possible to use discharge diagnoses as surrogate markers of infection. Studies examining the validity of discharge diagnoses identifying infections have previously to a large extent only focused on specific sites of infection, with varying results. The validity depends on which infection the patient presents with, the patient population, and setting examined [2]. Only a few studies have assessed the validity of ICD-10 codes for infections in general [3–5], and it is unknown if the validity changes in specific patient subgroups. The aims of this study were to determine, to which degree discharge diagnoses of infection could accurately identify commu- nity-acquired infections in an emergency department (ED) setting; and to assess if the sites of infection, baseline patient characteristics and disease severity affect the validity of the discharge diagnoses. PLOS ONE | www.plosone.org 1 March 2014 | Volume 9 | Issue 3 | e92891