Severity of pneumococcal pneumonia associated with genomic bacterial load.

Abstract

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. 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. 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). 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.