Severity of pneumococcal pneumonia associated with genomic bacterial load

Chest. 2009 Sep;136(3):832-840. doi: 10.1378/chest.09-0258. Epub 2009 May 11.


Background: There is a clinical need for more objective methods of identifying patients at risk for septic shock and poorer outcomes among those with community-acquired pneumonia (CAP). As viral load is useful in viral infections, we hypothesized that bacterial load may be associated with outcomes in patients with pneumococcal pneumonia.

Methods: Quantification of Streptococcus pneumoniae DNA level by real-time polymerase chain reaction (rt-PCR) was prospectively conducted on whole-blood samples from a cohort of 353 patients who were displaying CAP symptoms upon their admission to the ED.

Results: CAP caused by S pneumoniae was documented in 93 patients (36.5% with positive blood culture findings). A positive S pneumoniae rt-PCR assay finding was associated with a statistically significant higher mortality (odds ratio [OR], 7.08), risk for shock (OR, 6.29), and the need for mechanical ventilation (MV) [OR, 7.96]. Logistic regression, adjusted for age, sex, comorbidities, and pneumonia severity index class, revealed bacterial load as independently associated with septic shock (adjusted odds ratio [aOR], 2.42; 95% CI, 1.10 to 5.80) and the need for MV (aOR, 2.71; 95% CI, 1.17 to 6.27). An S pneumoniae bacterial load of >or= 10(3) copies per milliliter occurred in 29.0% of patients (27 of 93 patients; 95% CI, 20.8 to 38.9%) being associated with a statistically significant higher risk for septic shock (OR, 8.00), the need for MV (OR, 10.50), and hospital mortality (OR, 5.43).

Conclusion: In patients with pneumococcal pneumonia, bacterial load is associated with the likelihood of death, the risk of septic shock, and the need for MV. High genomic bacterial load for S pneumoniae may be a useful tool for severity assessment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • DNA, Bacterial / analysis*
  • DNA, Bacterial / genetics
  • Data Interpretation, Statistical
  • Female
  • Humans
  • Male
  • Middle Aged
  • Pneumonia, Pneumococcal / microbiology*
  • Pneumonia, Pneumococcal / mortality
  • Prospective Studies
  • Reverse Transcriptase Polymerase Chain Reaction
  • Risk Factors
  • Severity of Illness Index
  • Streptococcus pneumoniae / isolation & purification*


  • DNA, Bacterial