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Decling susceptibility of S. aureus and coagulase-negative staphylococci to vancomycin during an 18-year period in Denmark

Abstract number: P1732

Nielsen L., Arpi M.

Objectives: Several authors have reported treatment failure with vancomycin for staphylococci with MICs geqslant R: gt-or-equal, slanted4 mg/l. and it has been proposed to lower the breakpoint for sensitivity to vancomycin for staphylococci from 4 mg/l to 2 mg/l. The aim of the present study was to elucidate the trend over time of the susceptibility of S.aureus and coagulase-negative staphylococci (CNS) to vancomycin at Herlev University Hospital.

Methods: Herlev University Hospital is receiving specimens from the primary and secondary sector from the former Copenhagen County. During the 18 year period 1990–2007 vancomycin susceptibility testing of S. aureus and CNS was performed either by a disc diffusion method using Oxoid discs or by MIC determination with E-test (Biodisc). The disc diffusion method was applied to 2173 isolates of S.aureus and 9857 isolates of CNS and MIC determination was done on 1245 isolates of S. aureus and 1989 isolates of CNS. Results from the three periods 1990–1995, 1996–2001 and 2003–2007 were compared.

Results: The mean vancomycin zone for S. aureus decreased from 20.6 to 16.0 mm (p < 0.001) from the first time period till the last. For CNS a decrease was observed from 21.8 mm to 16.8 mm (p < 0.001). In the first two periods all S. aureus isolates had MICs leqslant R: less-than-or-eq, slant2 mg/l as compared to only 62.6% in the last period. In the last period 21.5% of the isolates had MICs geqslant R: gt-or-equal, slanted4 mg/l. The proportion of MICs leqslant R: less-than-or-eq, slant2 mg/l for CSN decreased from 77.8% in the first time period to 41.0% in the last period. In the last period 40.0% of CNS had MICs geqslant R: gt-or-equal, slanted4 mg/l.

Conclusion: Both S. aureus and CNS showed a declining sensitivity to vancomycin during the 18 year period. A trend which is worrying considering the reported risk of treatment failure when the MIC to vancomycin is geqslant R: gt-or-equal, slanted4 mg/l. This applied to 40% of CNS and 20% of S.aureus investigated and may be a problem especially when treating infections in difficult accessible foci.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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