Performance of PCR/Electrospray Ionization-Mass Spectrometry on Whole Blood for Detection of Bloodstream Microorganisms in Patients with Suspected Sepsis

Abstract

Blood culture (BC) often fails to detect bloodstream microorganisms in sepsis. However, molecular diagnostics hold great potential. The molecular method PCR/electrospray ionization-mass spectrometry (PCR/ESI-MS) can detect DNA from hundreds of different microorganisms in whole blood. The aim of the present study was to evaluate the performance of this method in a multicenter study including 16 teaching hospitals in the United States (n = 13) and Europe (n = 3). First, on testing of 2,754 contrived whole blood samples, with or without spiked microorganisms, PCR/ESI-MS produced 99.1% true-positive and 97.2% true-negative results. Second, among 1,460 patients with suspected sepsis (sepsis-2 definition), BC and PCR/ESI-MS on whole blood were positive in 14.6% and 25.6% of cases, respectively, with the following result combinations: BC positive and PCR/ESI-MS negative, 4.3%; BC positive and PCR/ESI-MS positive, 10.3%; BC negative and PCR/ESI-MS positive, 15.3%; and BC negative and PCR/ESI-MS negative, 70.1%. Compared with BC, PCR/ESI-MS showed the following sensitivities (coagulase-negative staphylococci not included): Gram-positive bacteria, 58%; Gram-negative bacteria, 78%; and Candida species, 83%. The specificities were >94% for all individual species. Patients who had received prior antimicrobial medications (n = 603) had significantly higher PCR/ESI-MS positivity rates than patients without prior antimicrobial treatment-31% versus 22% (P < 0.0001)-with pronounced differences for Gram-negative bacteria and Candida species. In conclusion, PCR/ESI-MS showed excellent performance on contrived samples. On clinical samples, it showed high specificities, moderately high sensitivities for Gram-negative bacteria and Candida species, and elevated positivity rates during antimicrobial treatment. These promising results encourage further development of molecular diagnostics to be used with whole blood for detection of bloodstream microorganisms in sepsis.

Keywords: PCR/ESI-MS; bacteremia; direct detection; sepsis.

FIG 1

Flow chart of study population.

FIG 2

Proportion of patients positive by BC and/or PCR/ESI-MS altogether (A) and among patients with two sets and one set of BC bottles (B).

FIG 3

Proportion of patients positive by BC and/or PCR/ESI-MS for Gram-positive and Gram-negative bacteria.

FIG 4

Individual organisms detected by BC and PCR/ESI-MS.

FIG 5

Proportion of cases positive by BC and/or PCR/ESI-MS in patients without (n = 857) and with (n = 603) prior antimicrobial treatment, overall (A) and broken down by detection of Gram-positive (B) and Gram-negative (C) organisms.

FIG 6

Proportions of patients without (A) and with (B) any prior antimicrobials and positive for major individual bacteria. An asterisk indicates significant (P < 0.05) differences regarding total proportion of positives (BC and/or PCR/ESI-MS) between cases without and with prior antimicrobials.

FIG 7

Proportion of patients positive for Candida species by BC and/or PCR/ESI-MS, in relation to prior antimicrobial medication.

FIG 8

Semiquantitative levels for Staphylococcus aureus DNA (A) and Escherichia coli DNA (B) related to BC results in patients with PCR/ESI-MS positive for S. aureus and E. coli.