Centers for Disease Control
Assessment of testing for and completeness reporting of vancomycin-
resistant enterococci -- Connecticut, 1994
Morb Mortal Weekly Rep
(Apr) 45:No. 14 1996
The full text article is below:
From 1989 through 1993, the proportion of enterococcal
isolates resistant to vancomycin (VRE) reported to CDC's National
Nosocomial Infections Surveillance (NNIS) system increased from
0.3% to 7.9% (1). Since January 1994, clinical laboratories in
Connecticut have been required to report all sterile-site VRE
isolates to the Connecticut Department of Public Health (CDPH) to
determine the epidemiology of VRE infection in the state. In 1995,
CDPH surveyed all clinical laboratories in the state to identify
microbiologic methods used to determine antimicrobial
susceptibility of enterococcal isolates and to assess the
completeness of reporting in 1994. This report summarizes the
survey findings and the assessment of reporting for VRE, which
confirmed for the first time that VRE infections were occurring
statewide in Connecticut.
During April 1995, CDPH mailed questionnaires to the
laboratory directors at the 125 clinical laboratories in
Connecticut and received completed questionnaires from the 46 (37%)
laboratories with the capacity to identify enterococcal isolates
and perform vancomycin-susceptibility testing of enterococci. A
total of 37 laboratories were hospital-affiliated; nine were
commercial. Of the 46 laboratories, 33 (72%) tested all
enterococcal isolates for vancomycin resistance, and 13 (28%)
tested isolates from sterile sites only.
In 1994, these 46 laboratories processed 11,290 enterococcal
isolates from both sterile (e.g., blood) and nonsterile (e.g.,
stool) sites (median: 286 isolates, range: two-1109 isolates per
laboratory); of these, 517 (5%) were reported to be vancomycin
resistant. A total of 24 (52%) laboratories also performed
speciation of enterococci. Of the 3202 isolates identified to
species, 2556 (80%) were Enterococcus faecalis, and 646 (20%) were
E. faecium; of these, 12 (less than 0.1%) and 120 (19%),
respectively, were reported to be vancomycin resistant.
Methods of vancomycin-susceptibility testing varied among
laboratories: 25 (54%) used the Kirby-Bauer method; 15 (33%), the
automated Microscan (Dade International, West Sacramento,
California)* system; nine (20%), the automated Vitek (bioMerieux,
Hazlewood, Missouri) system; six (13%), vancomycin screen agar;
four (9%), minimum inhibitory concentration panels; two (4%), the
automated Sensititre (Accumed International, West Lake, Ohio)
system; and two (4%), the automated Uniscept (bioMerieux,
Hazlewood, Missouri) system. Nineteen (41%) laboratories used at
least one duplicate test. Six laboratories using the Microscan and
seven using the Vitek used a second method because of reports of
failure to accurately detect antimicrobial resistance in
enterococci with these systems (2,3).
To assess completeness of VRE reporting to the state health
department, during May-July 1995, CDPH contacted laboratory and
infection-control personnel from the 37 hospital-affiliated
laboratories to identify sterile-site VRE isolates not previously
reported in 1994. Passive reporting identified 34 sterile-site VRE
isolates in 1994; the CDPH survey identified an additional 27
isolates, indicating that passive laboratory reporting identified
34 (56%) of 61 sterile-site VRE isolates. Of the 61 sterile-site
VRE isolates identified through passive surveillance and the CDPH
survey, 47 (77%) were from blood, representing 0.02% of the 238,937
bloodstream pathogens isolated by these laboratories in 1994.
Reported by: ZF Dembek, PhD, ML Cartter, MD, JL Hadler, MD, State
Epidemiologist, Connecticut Dept of Public Health. Hospital
Infections Program, National Center for Infectious Diseases, CDC.
Editorial Note: Because enterococci commonly are resistant to
vancomycin and other widely used antimicrobials, infections with
these organisms are virtually untreatable (4). Laboratory-based
surveillance is critical in programs to detect, control, and
prevent antimicrobial resistance in enterococci and other organisms
(5). Connecticut is the first state to require statewide
laboratory-based reporting of VRE isolates obtained from sterile
During 1994, only 56% of all sterile-site VRE isolates
initially were reported to CDPH. Efforts to increase laboratory
reporting in Connecticut have included dissemination to all
laboratory directors of CDPH publications that emphasize the
importance of reporting and regular communication between CDPH and
laboratory directors. These findings also underscore the importance
of periodic validation of completeness of reporting of
Since the first isolation of VRE in 1988, prevalence of
infection has increased in both hospitalized patients and residents
of long-term-care facilities (LTCFs), resulting in management and
treatment problems (6). Although nosocomial transmission of VRE has
been well documented, it is unclear whether the increase in the
number of VRE isolates from patients of LTCFs (7) reflects changes
in the epidemiology of VRE or increases in admission to LTCFs of
patients who have been hospitalized in acute-care hospitals in
which VRE is endemic. In response to concerns about admission of
VRE-positive patients to LTCFs, CDPH has collaborated with
infection-control personnel to develop guidelines for prevention of
VRE infection and management of persons who are infected or
colonized with VRE.
This report also highlights two issues for laboratories.
First, because methods used to test vancomycin susceptibility in
enterococci vary widely, as in Connecticut, and some methods fail
to detect antimicrobial resistance (2,3), proficiency testing and
standardization of acceptable methods may be appropriate for
laboratories performing vancomycin-susceptibility testing of
enterococci. Second, laboratories that test for vancomycin
susceptibility should consider testing isolates to the species
level. In Connecticut, only 52% of the laboratories surveyed
performed species identification. Species identification is
important in assessing the accuracy of susceptibility
determinations, understanding the epidemiology of different
enterococci strains, and measuring the prevalence of previously
unknown clinical pathogens (e.g., E. galinerum, which is known to
intrinsically have at least intermediate resistance to vancomycin
1. CDC. Nosocomial enterococci resistant to vancomycin--United
States, 1989-1993. MMWR 1993;42:597-9.
2. Tenover FC, Tokars J, Swenson J, Paul S, Spitalny K, Jarvis B.
Ability of clinical laboratories to detect antimicrobial
agent-resistant enterococci. J Clin Microbiol 1993;31:1695-9.
3. Zabransky RJ, DiNuzzo AR, Huber MB, Woods GL. Detection of
vancomycin resistance in enterococci by the Vitek AMS system. Diagn
Microbiol Infect Dis 1994;20:113-6.
4. Spera RV, Farber BF. Multiply resistant Enterococcus faecium:
the nosocomial pathogen of the 1990's. JAMA 1992;268:2563-4.
5. CDC. Statewide surveillance for antibiotic-resistant bacteria--New Jersey,
6. Kaplan AH, Gilligan PH, Facklarn RR. Recovery of resistant
enterococci during vancomycin prophylaxis. J Clin Microbiol
7. Korten V, Murray BE. The nosocomial transmission of enterococci.
Current Opinion in Infectious Diseases 1993;6:498-505.
* Use of trade names and commercial sources is for identification
only and does not imply endorsement by the Public Health Service or
the U.S. Department of Health and Human Services.