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 4 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 19902007 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 19901995, 19962001 and 20032007 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 2 mg/l as compared to only 62.6% in the last period. In the last period 21.5% of the isolates had MICs 4 mg/l. The proportion of MICs 2 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 4 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 4 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 name:||18th European Congress of Clinical Microbiology and Infectious Diseases|
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