title: Clinical impact of combined viral and bacterial infection in patients with community-acquired pneumonia.
abstract: BACKGROUND
  New methods for identifying respiratory pathogens have led to several reports of a high yield of mixed infections in patients with community-acquired pneumonia (CAP). The clinical impact of these findings has, however, not been fully evaluated. We aimed to compare patients with a pure bacterial etiology with those with findings of both bacteria and virus regarding severity of illness and length of hospital stay.
  
  
  METHODS
  Adults with CAP admitted to Karolinska University Hospital were studied prospectively (N = 184). Microbiological methods included cultures from blood, sputum and nasopharyngeal secretions; sputum samples analyzed with quantitative real-time polymerase chain reaction for Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis; nasopharyngeal specimens analyzed with polymerase chain reaction and serology for Mycoplasma pneumoniae, Chlamydophila pneumoniae and viruses common in the respiratory tract; and urine antigen assays for detecting pneumococcal and Legionella pneumophila antigens. The pneumonia severity index (PSI) was used to assess the severity of illness.
  
  
  RESULTS
  The likelihood of getting a score corresponding to PSI classes IV or V was higher in patients with findings of both bacteria and virus than in those with a bacterial pathogen alone (odds ratio 4.98, 95% confidence interval 2.09-11.89; p < 0.001). The median length of hospital stay was 7 days among patients with mixed infections and 4 days among those with a bacterial etiology alone (p = 0.018).
  
  
  CONCLUSIONS
  Patients infected with a virus and a bacterial pathogen more often develop severe CAP and have a longer hospitalization than those with a bacterial etiology alone.
authors.affiliation: Karolinska Institutet, Department of Medicine, Solna, Infectious Diseases Unit, Karolinska University Hospital, Stockholm, Sweden. niclas.johansson@karolinska.se
authors.forename: Niclas
authors.initials: N
authors.lastname: Johansson
authors.forename: Mats
authors.initials: M
authors.lastname: Kalin
authors.forename: Jonas
authors.initials: J
authors.lastname: Hedlund
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D016009:Chi-Square Distribution; D017714:Community-Acquired Infections / Q000453:epidemiology / Q000382:microbiology* / Q000821:virology; D005260:Female; D006801:Humans; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D018410:Pneumonia, Bacterial / Q000453:epidemiology / Q000382:microbiology* / Q000821:virology; D011024:Pneumonia, Viral / Q000453:epidemiology / Q000382:microbiology* / Q000821:virology; D011379:Prognosis; D011446:Prospective Studies; D060888:Real-Time Polymerase Chain Reaction; D014780:Viruses / Q000145:classification / Q000302:isolation & purification