title: Predictors of positive or negative legionella urinary antigen test in community-acquired pneumonia.
abstract: BACKGROUND
  Legionella pneumonia remains a diagnostic challenge. The legionella urinary antigen test (LUT) primarily detects Legionella pneumophila serogroup 1, accounting for 64% of Danish cases, and is often the only legionella test performed. We aimed to identify variables predictive of a positive or negative test result and to explore how the LUT was used in clinical practice.
  
  
  METHODS
  The study was an audit-based cohort study. LUT-positive patients were compared with three randomly selected age- and gender-matched LUT-negative referent patients admitted at a Danish university hospital during 2003-2013. Data were extracted from charts and databases. Positive and negative likelihood ratios (LR+ and LR-) were calculated. For CURB-65 and sepsis, sensitivity analyses were made due to incomplete data.
  
  
  RESULTS
  In all, 25 cases were compared with 75 referents. Factors associated with LUT positivity included recent travel outside Scandinavia (LR + 5.3), Na(+) < 130 mEq/L (LR + 4.3), confusion (LR + 4.2), C-reactive protein (CRP) > 200 mg/L (LR + 3.5), temperature > 39 °C (LR + 3.5), and CURB-65 score ≥ 3 (LR + 3.0-15.0, depending on the model). Decreasing the likelihood of LUT positivity were CRP < 200 mg/L (LR- 0.1), absence of sepsis (LR- 0.1-0.2, depending on the model), absence of tachycardia (heart rate < 90) (LR- 0.2) and normal pulmonary auscultation (LR- 0.3). Additional legionella tests were performed in 60% of the cases and 13% of the referents.
  
  
  CONCLUSIONS
  Classical features of severe pneumonia are associated with a positive LUT. The LUT is often used inappropriately and should be accompanied by PCR analysis.
authors.affiliation: Department of Infectious Diseases, Aalborg University Hospital.
authors.forename: Torsten
authors.initials: T
authors.lastname: Roed
authors.forename: Henrik C
authors.initials: HC
authors.lastname: Schønheyder
authors.forename: Henrik
authors.initials: H
authors.lastname: Nielsen
mesh_terms: D000368:Aged; D000942:Antigens, Bacterial / Q000652:urine*; D015331:Cohort Studies; D017714:Community-Acquired Infections; D003718:Denmark; D005260:Female; D006801:Humans; D016952:Legionella pneumophila / Q000276:immunology*; D007877:Legionnaires' Disease / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D011014:Pneumonia / Q000382:microbiology* / Q000652:urine; D012307:Risk Factors
chemical_list: D000942:Antigens, Bacterial
keywords: Legionella; diagnosis; pneumonia; test