Impact of rapid in situ hybridization testing on coagulase-negative staphylococci positive blood cultures

OBJECTIVES: To evaluate the impact of the rapid differentiation of Staphylococcus aureus from coagulase-negative staphylococci (CoNS) in blood cultures using peptide nucleic acid fluorescence in situ hybridization (PNA FISH) on vancomycin usage, length of patient hospital stay and hospital costs. DESIGN: This was a retrospective, cost-effective analysis of PNA FISH in its initial 3 month implementation period in 2004 in a 650 bed academic medical centre. Blood cultures with Gram-positive cocci in clusters (GPCC) that were negative for S. aureus using the PNA FISH assay were compared with an untested control group in the same period that had similar illness severity and location. We evaluated the effectiveness of the early identification of CoNS by ruling out S. aureus in conjunction with an antimicrobial team (AMT) on antimicrobial therapy, patient length of stay and hospital costs. RESULTS: A total of 139 blood cultures positive with GPCC had PNA FISH results while 84 in the control group did not. Evaluable criteria were met in 53 patients in the PNA FISH group and 34 in the control group. When comparing the results obtained from using the PNA FISH assay with those for the control group, there was a significant reduction in median length of hospital stay from 6 to 4 days (P < 0.05, CI 0.95-1.87) and a trend towards less vancomycin usage with a decrease in associated hospital costs of approximately Dollars 4000 per patient. CONCLUSIONS: The PNA FISH assay is rapid, accurate and reliable and in association with an AMT could decrease hospital length of stay in patients with CoNS bacteraemia in non-intensive care unit settings and prevent excessive vancomycin usage.