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Microbial aetiology of community-acquired pneumonia and its relation to severity
  1. Catia Cillóniz1,5,
  2. Santiago Ewig2,
  3. Eva Polverino1,5,
  4. Maria Angeles Marcos3,
  5. Cristina Esquinas1,
  6. Albert Gabarrús1,
  7. Josep Mensa4,
  8. Antoni Torres1,5
  1. 1Servei de Pneumologia, Institut del Tòrax, Hospital Clinic, IDIBAPS, Universitat de Barcelona, Barcelona, Spain
  2. 2Department of Pneumology, Thoraxzentrum Ruhrgebiet, Herne und Bochum, Germany
  3. 3Department of Microbiology, Hospital Clínic, Barcelona, Spain
  4. 4Department of Infectious Diseases, Hospital Clínic, Barcelona, IDIBAPS, Spain
  5. 5Centro de Investigación Biomédica En Red-Enfermedades Respiratorias (CibeRes, CB06/06/0028), Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación, Spain
  1. Correspondence to Antoni Torres, Servei de Pneumologia, Institut Clínic de Pneumologia i Cirurgia Toràcica, Hospital Clinic, Villarroel 170, Barcelona 08036, Spain; atorres{at}


Background The distribution of the microbial aetiology and mortality of community-acquired pneumonia (CAP) was investigated in relation to the clinical setting and severity scores (pneumonia severity index (PSI) and confusion, blood urea nitrogen, respiratory rate, blood pressure, age (CURB-65)).

Methods 3523 patients with CAP were included (15% outpatients, 85% inpatients). The distribution of the microbial aetiology in relation to the clinical setting and severity scores (PSI, CURB-65) and the relative mortality of different aetiologies across the severity scores were analysed.

Results The aetiology was established in 1463 patients (42%), of whom 257 died (7%). The ranking of aetiologies varied according to site of care, with increasing frequency of Streptococcus pneumoniae and mixed aetiologies and decreasing frequency of atypical pathogens in hospitalised patients and those in ICUs. The distribution of aetiologies according to severity scores showed corresponding patterns; however, the severity scores were more sensitive to Gram-negative enteric bacilli (GNEB) and Pseudomonas aeruginosa and less sensitive in identifying mixed aetiologies as moderate- and high-risk conditions. Mortality rates according to aetiology and severity scoring showed increasing mortality rates for all pathogens except atypical pathogens. S pneumoniae had the highest number of deaths while GNEB, P aeruginosa, Staphylococcus aureus and mixed aetiologies had the highest mortality rates. Legionella pneumophila was similarly distributed according to site of care and prognostic scores.

Conclusions CAP due to atypical bacterial pathogens is recognised both clinically and by severity scoring as a low-risk condition. Severity scores are more sensitive in identifying patients with GNEB and P aeruginosa as moderate- and high-risk aetiologies whereas mixed aetiologies may be underestimated.

  • Community-acquired pneumonia
  • microbial aetiology
  • severity assessment
  • bacterial infection
  • clinical epidemiology
  • pneumonia
  • respiratory infection

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  • Funding CibeRes (CB06/06/0028)-ISCiii, 2009 SGR 911 and IDIBAPS.

  • Competing interests None.

  • Ethics approval It was not considered necessary to obtain ethical approval as this is a non-interventional study based on an epidemiological database of prospectively and routinely collected data.

  • Provenance and peer review Not commissioned; externally peer reviewed.