Microbial and clinical determinants of time-to-positivity in patients with bacteraemia

Use of PCR coupled with electrospray ionization mass spectrometry for rapid identification of bacterial and yeast bloodstream pathogens from blood culture bottles

Sepsis is among the top 10 causes of mortality in the United States. Rapid administration of antibiotics is one of the most important contributors to patient survival, yet only a limited number of methods exist for rapid identification of microbes cultivated from bloodstream infections, which can lead to sepsis. While traditional single-target molecular methods have been shown to greatly improve survival for septic patients by enabling rapid deescalation of broad-spectrum antibiotics, multiplex methods offer even greater possibilities. A novel multiplex method, PCR coupled to electrospray ionization mass spectrometry (PCR/ESI-MS), was used to identify the genus and species of microorganisms found to cause human bloodstream infections. DNA was directly extracted from 234 BacT-Alert blood culture bottles, and results were compared to those obtained by clinical reference standard methods. The study results demonstrated 98.7% and 96.6% concordance at the genus and species levels, respectively. Mixtures of microbes were identified in 29 blood culture bottles, including mixed species of the same genus, as well as mixtures containing Gram-positive and Gram-negative organisms, exemplifying the PCR/ESI-MS capability to identify multiple organisms simultaneously without the need for cultivation. This study demonstrates high analytical accuracy in comparison to routine subculture of blood culture bottles and phenotypic identification of microbes. Without foreknowledge of the microorganisms potentially present, the PCR/ESI-MS methods can deliver accurate results in as little as 5 to 6 h after a positive alarm from the automated blood culture system; however, current batch mode testing limits the method's clinical utility at this time.

Correlation between time to positivity of blood cultures with clinical presentation and outcomes in patients with Klebsiella pneumoniae bacteraemia: prospective cohort study

Time to positivity (TTP) of blood cultures in patients with bacteraemia is considered to be a predictor of outcome for some bacterial species. Two hundred and thirty-one patients with Klebsiella pneumoniae monomicrobial bacteraemia at a hospital from 1 January to 31 December 2007 were prospectively enrolled. TTP <7 h (46 patients, 19.9%) was associated with a higher Pittsburg bacteraemia score (6.2 +/- 5.5 vs. 3.7 +/- 4.3, p 0.002), fewer non-fatal diseases by the McCabe classification (39.1% vs. 64.9%, p 0.002), a higher percentage of patients with liver cirrhosis, active malignancy, and chemotherapy within 3 months (28.3% vs. 11.9%, p 0.007; 28.3% vs. 14.6%, p 0.031; 23.9% vs. 5.4%, p <0.001), more primary bacteraemia (45.7% vs. 22.2%, p 0.002), and a higher 30-day mortality rate (47.8% vs. 21.1%, p <0.001). Risk factors for 30-day mortality in the univariate analysis included higher Pittsburg bacteraemia score (5.8 +/- 5.3 vs. 3.7 +/- 4.3, p 0.002), primary bacteraemia (41.0% vs. 21.8%, p 0.004), TTP <7 h (36.1% vs. 14.1%, p <0.001), and the presence of active malignancy (29.5% vs. 12.9%, p 0.004). In the multivariate analysis, higher Pittsburg bacteraemia score (OR 1.07; 95% CI 1.01-1.14), TTP <7 h (OR 2.46; 95% CI 1.20-5.05) and active malignancy (OR 2.21; 95% CI 1.03-4.73) were the significant factors associated with 30-day mortality. In the Kaplan-Meier survival curve, short TTP was significantly associated with mortality at all time-points after admission. TTP of blood cultures, interpreted with a cut-off point of <7 h, in patients with K. pneumoniae bacteraemia can provide useful prognostic information.