title: Can an etiologic agent be identified in adults who are hospitalized for community-acquired pneumonia: results of a one-year study.
abstract: BACKGROUND
  Determining the cause of community-acquired pneumonia (CAP) remains problematic. In this observational study, we systematically applied currently approved diagnostic techniques in patients hospitalized for CAP in order to determine the proportion in which an etiological agent could be identified.
  
  
  METHODS
  All patients admitted with findings consistent with CAP were included. Sputum and blood cultures, urine tests for pneumococcal and Legionella antigens, nasopharyngeal swab for viral PCR, and serum procalcitonin were obtained in nearly every case. Admission-related electronic medical records were reviewed in entirety.
  
  
  RESULTS
  By final clinical diagnosis, 44 patients (17.0%) were uninfected. A causative bacterium was identified in only 60 (23.2%) cases. PCR identified a respiratory virus in 42 (16.2%), 12 with documented bacterial coinfection. In 119 (45.9%), no cause for CAP was found; 69 (26.6%) of these had a syndrome indistinguishable from bacterial pneumonia. Procalcitonin was elevated in patients with bacterial infection and low in uninfected patients or those with viral infection, but with substantial overlap.
  
  
  CONCLUSIONS
  Only 23.2% of 259 patients admitted with a CAP syndrome had documented bacterial infection; another 26.6% had no identified bacterial etiology, but findings closely resembled those of bacterial infection. Nevertheless, all 259 received antibacterial therapy. Careful attention to the clinical picture may identify uninfected patients or those with viral infection, perhaps with reassurance by a non-elevated procalcitonin. Determining an etiologic diagnosis remains elusive. Better discriminators of bacterial infection are sorely needed.
authors.affiliation: Medical Care Line (Infectious Disease Section), Michael E. DeBakey Veterans Affairs Medical Center, Houston, TX, USA. dmusher@bcm.edu
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Musher
authors.forename: Ingrid L
authors.initials: IL
authors.lastname: Roig
authors.forename: Guillermo
authors.initials: G
authors.lastname: Cazares
authors.forename: Charles E
authors.initials: CE
authors.lastname: Stager
authors.forename: Nancy
authors.initials: N
authors.lastname: Logan
authors.forename: Hossam
authors.initials: H
authors.lastname: Safar
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D001419:Bacteria / Q000145:classification / Q000302:isolation & purification*; D017714:Community-Acquired Infections / Q000175:diagnosis / Q000209:etiology* / Q000382:microbiology / Q000821:virology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011014:Pneumonia / Q000175:diagnosis / Q000209:etiology* / Q000382:microbiology / Q000821:virology; D014780:Viruses / Q000145:classification / Q000302:isolation & purification*
chemical_list: D000900:Anti-Bacterial Agents