Assessment of the usefulness of sputum culture for diagnosis of community-acquired pneumonia using the PORT predictive scoring system

Arch Intern Med. 2004 Sep 13;164(16):1807-11. doi: 10.1001/archinte.164.16.1807.


Background: The usefulness of sputum culture in guiding microbiological diagnosis of community-acquired pneumonia is controversial. We evaluate and assess it using the Patients Outcome Research Team (PORT) predictive scoring system.

Methods: A cohort of 1669 patients with community-acquired pneumonia was studied. Before administering antibiotic therapy, sputum was collected and its quality evaluated. Samples were gram stained and those of good quality were assessed for a predominant morphotype (PM). Sputum cultures were processed according to standard protocols.

Results: A sputum sample was obtained from 983 (59%) of the 1669 patients and 532 (54%) of the samples were of good quality. There was a PM in 240 (45%) of the latter samples (ie, for 14.4% of the 1669 patients) and there was no PM in 292 (55%). Culture yielded a microorganism in 207 (86%) of the 240 samples with PM and 57 (19.5%) of the 292 samples without PM (P<.05). Rates of sputum obtained, good-quality sputum specimens, PM identification, and positive culture were not significantly different among the PORT-score groups of patients (P>.05). The sensitivity and specificity of the gram-positive diplococci identification in the sputum culture of Streptococcus pneumoniae were 60% and 97.6%, and the positive and negative predictive values were 91% and 85.3%, respectively.

Conclusions: Good-quality sputum with PM could be obtained in only 14.4% of all patients. A PORT-score group in which sputum could be of greater usefulness in identifying the causative organism could not be identified. The presence of gram-positive diplococci in gram-stained sputum culture was highly specific for S pneumoniae.

Publication types

  • Comparative Study

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Anti-Bacterial Agents / therapeutic use
  • Cohort Studies
  • Colony Count, Microbial
  • Community-Acquired Infections / diagnosis
  • Community-Acquired Infections / drug therapy
  • Community-Acquired Infections / microbiology*
  • Cough
  • Female
  • Humans
  • Male
  • Microbial Sensitivity Tests
  • Middle Aged
  • Pneumonia / diagnosis
  • Pneumonia / drug therapy
  • Pneumonia / microbiology*
  • Sensitivity and Specificity
  • Sputum / microbiology*


  • Anti-Bacterial Agents