Chest
Volume 136, Issue 3, September 2009, Pages 832-840
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Original Research
Community-Acquired Pneumonia
Severity of Pneumococcal Pneumonia Associated With Genomic Bacterial Load

https://doi.org/10.1378/chest.09-0258Get rights and content

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 ≥ 103 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.

Section snippets

Study Design

This was a prospective study of adult patients hospitalized with CAP. Data and blood samples were collected in the ED. Data were entered into an electronic database for analysis. Patients were observed for the development of the predefined end points of septic shock development and the need for MV from the time they were admitted to the ED until they were discharged from the hospital. Secondary outcomes were the development of AKI and ARDS, and in-hospital mortality.

Study Population

Adult patients admitted to

Study Population

A total of 353 white patients with CAP were included in the study, of whom 93 were documented as a having a diagnosis of definite CAP (n = 44) or probable CAP (n = 49) caused by S pneumoniae, and 260 patients had no evidence of S pneumoniae and a negative rt-PCR result. A description of the techniques used to detect S pneumoniae is shown in Table A1 (in the online supplemental material). Clinical characteristics of the 260 patients with negative bacterial load and no evidence of S pneumoniae

Discussion

This study confirms the association between a high quantitative bacterial genomic load of S pneumoniae in blood samples and increased mortality. It also reveals an association between bacterial load and the development of septic shock or the need for MV. The implication of these findings is that a sample obtained for bacterial load measurement will provide valuable prognostic information. Our observations also reveal some insight into the mechanisms that underlie the risk factors associated

Acknowledgments

Author contributions: Drs. Rello and Lisboa were responsible for analysis of data and writing the first draft of the article; all remaining authors contributed scientifically to the final version of the article. Drs. Rello, Gallego, Lujan, Lopez, and Lisboa enrolled patients, recorded variables, conducted the follow-up, and collected samples. Drs. Waterer and Kee, and Mr. Kay were responsible for performing the quantitative reverse transcription PCR assay.

Financial/nonfinancial disclosures: The

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Funding/Support: This study was funded by FIS 04/1500, Fondo de Investigaciones Sanitarias, CIBER Enfermedades Respiratorias (CIBERes 06/06/0036), and AGAUR (2005/SGR/920). Dr. Waterer is supported by the National Health and Medical Research Council of Australia.

Presented in part at the 2008 American Thoracic Society Conference, Toronto, ON, Canada.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).

*

A complete list of members of the DNA-Neumococo Study Group is located in the Appendix.

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