title: How well do discharge diagnoses identify hospitalised patients with community-acquired infections?--a validation study.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Emergency Medicine, Odense University Hospital, Odense, Denmark.
authors.forename: Daniel Pilsgaard
authors.initials: DP
authors.lastname: Henriksen
authors.affiliation: Department of Infectious Diseases, Odense University Hospital, Odense, Denmark.
authors.forename: Stig Lønberg
authors.initials: SL
authors.lastname: Nielsen
authors.affiliation: Department of Respiratory Medicine, Odense University Hospital, Odense, Denmark.
authors.forename: Christian Borbjerg
authors.initials: CB
authors.lastname: Laursen
authors.affiliation: Department of Clinical Pharmacology, University of Southern Denmark, Odense, Denmark.
authors.forename: Jesper
authors.initials: J
authors.lastname: Hallas
authors.affiliation: Department of Infectious Diseases, Odense University Hospital, Odense, Denmark.
authors.forename: Court
authors.initials: C
authors.lastname: Pedersen
authors.affiliation: Department of Emergency Medicine, Odense University Hospital, Odense, Denmark.
authors.forename: Annmarie Touborg
authors.initials: AT
authors.lastname: Lassen
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D003141:Communicable Diseases / Q000175:diagnosis / Q000401:mortality / Q000628:therapy; D003718:Denmark; D004636:Emergency Service, Hospital; D005260:Female; D006801:Humans; D008297:Male; D015588:Observer Variation; D010351:Patient Discharge; D012042:Registries; D012720:Severity of Illness Index