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Journal of Clinical Microbiology, July 1999, p. 2148-2152, Vol. 37, No. 7
Hospital Infections Program, Centers for
Disease Control and Prevention, Atlanta, Georgia
30333,1 and Consejeria de Servicios
Sociales, Oviedo, Principado de Asturias, 33005, Spain2
Received 23 December 1998/Returned for modification 1 February
1999/Accepted 25 March 1999
Studies in a variety of U.S. clinical laboratories have
demonstrated difficulty in detecting intermediate and low-level
vancomycin-resistant enterococci (VRE). The misclassification of "at
least intermediate resistant isolates" as vancomycin susceptible may
have both clinical implications and a negative impact on measures to
control the spread of VRE. No published study has assessed the ability
of clinical laboratories in Europe to detect VRE. So, the apparent low
prevalence of VRE in European hospitals may be, in part, secondary to
the inability of these laboratories to detect all VRE. In an effort to
assess European laboratories' proficiency in detecting VRE, we
identified 22 laboratories in Spain and asked them to test four VRE
strains and one susceptible enterococcal strain from the Centers for
Disease Control and Prevention collection. Each organism was tested by
the routine antimicrobial susceptibility testing method used by each
laboratory. Overall, VRE were correctly identified in 61 of 88 (69.1%)
instances. The accuracy of VRE detection varied with the level of
resistance and the antimicrobial susceptibility method. The
high-level-resistant strain (Enterococcus faecium; MIC, 512 µg/ml) was accurately detected in 20 of 22 (91.3%) instances,
whereas the intermediate-resistant isolate (Enterococcus gallinarum; MIC, 8 µg/ml) was accurately detected in only 11 of 22 (50%) instances. Classification errors occurred in 27 of 88 (30.9%) instances. Misclassification as vancomycin susceptible was the
most common error (16 of 27 [59.3%] instances). Our study shows that
the participating Spanish laboratories had an overall acceptable
proficiency in detecting VRE but that a substantial proportion of
VRE isolates with low or intermediate levels of resistance were
not detected. We recommend that studies be conducted to validate
laboratory proficiency testing as an important step in the prevention
and control of the spread of antimicrobial resistance.
0095-1137/99/$04.00+0
Proficiency of Clinical Laboratories in Spain in
Detecting Vancomycin-Resistant Enterococcus spp.
*
Corresponding author. Mailing address: Hospital
Infections Program, Centers for Disease Control and Prevention MS E69,
1600 Clifton Rd., Atlanta, GA 30333. Phone: (404) 639-6413. Fax: (404) 639-6459. E-mail: wrj1{at}cdc.gov.
The investigators participating in The Spanish VRE Study Group are
listed in the appendix.
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