Effect of Antimicrobial Treatment Duration on recovery of Bacteria in Sterile Specimens Submitted for Culture
Early initiation of antibiotics results in cultures that are unrevealing, resulting in potentail over use of broad-spectrum antibiotics. We performed a prospective study of PCR & electrospray ionization mass spectrometry (PCR/ESI-MS) assay in development for detection of bacteria directly from sterile surgical specimens obtained after antibiotic treatment had been initiated.
We prospectively identified 111 cases of suspected bacterial infection in which sterile specimens were submitted for culture after the initiation of antibiotics. Patients were stratified based on days of antibiotic treatment (DOT). Conventional aerobic and anaerobic culture results were compared to PCR/ESI-MS. Agreement was assessed by Kappa score.
PCR/ESI-MS detected pathogens more often than conventional culture: 71% (79/111) vs. 32% (36/111). The overall Kappa score was 0.294, consistent with poor agreement. Culture and PCR/ESI-MS had strong agreeement (Kappa = 0.73) for patients with < 2 days of antibiotic treatment (Table 1). For patients in the two longer treatment groups, PCR/ESI-MS was more likely to detect bacterial pathogens, and the discordance between culture and PCR/ESI-MS results as measured by Kappa was more than would be expected by chance.
Table 1. PCR&ESI-MS vs Culture results Stratified by DOT (N=111)
N PCR&ESIMS-/Culture- PCR&ESIMS-/Culture+ PCR&ESIMS+/Culture+ PCR&ESIMS+/Culture- Kappa (95% CI)
DOT < 2 45 16 1 23 5 0.73 (0.53 – 0.93)
DOT 3 - 7 37 8 0 7 22 0.12 (0.01 – 0.23)
DOT > 8 29 7 0 5 17 0.12 (-0.005 – 0.25)
In patients treated with > 2 days of antimicrobial treatment prior to collection of samples, PCR-ESI/MS was significantly more likely than conventional culture to detect pathogic bacteria directly from sterile surgical specimens. PCR/ESI-MS results were not significantly different from conventional culture for specimens collected within 48 hours of initiation of antibiotics. The advantage with antibiotic treatment durations > 2 days does not appear to demonstrate a dose response relationship. PCR/ESI-MS may provide future opportunities to target antimicrobial therapy and salvage both individual treatment regimens and institutional antimicrobial stewardship efforts when patients have received more than 2 days of antimicrobial treatment prior to diagnostic testing.
R. Bonomo, AstraZeneca: Grant Investigator, Grant recipient
Merck: Grant Investigator, Grant recipient
Rib-X: Grant Investigator, Grant recipient
Steris: Grant Investigator, Grant recipient
TetraPhase: Scientific Advisor, nothing
NIH: Grant Investigator, Grant recipient
VA Merit Review: Grant Investigator, Grant recipient