Staphylococcus aureus with Reduced Susceptibility to Vancomycin -- United States, 1997

Staphylococcus aureus is one of the most common causes of both hospital- and community-acquired infections worldwide, and the antimicrobial agent vancomycin has been used to treat many S. aureus infections, particularly those caused by methicillin-resistant S. aureus (MRSA). In 1996, the first documented case of infection caused by a strain of S. aureus with intermediate levels of resistance to vancomycin (VISA; minimum inhibitory concentration {MIC}=8 ug/mL) was reported from Japan (1). This report describes the first isolation of VISA from a patient in the United States, which may be an early warning that S. aureus strains with full resistance to vancomycin will emerge.

In July 1997, VISA-associated peritonitis was diagnosed in a patient who was being treated with long-term ambulatory peritoneal dialysis. During January 1996-June 1997, the patient had been treated with multiple courses of both intraperitoneal and intravenous vancomycin for repeated episodes of MRSA-associated peritonitis. The patient received medical care primarily at home; when hospitalized, the patient had been placed on contact isolation precautions because of known MRSA.

Six isolates of S. aureus obtained from one specimen from this patient in July were sent to CDC for species confirmation and antimicrobial susceptibility testing. The identity of these isolates was confirmed, and of the six, one demonstrated a vanco-mycin MIC of 8 ug/mL (National Committee for Clinical Laboratory Standards breakpoints for susceptibility: susceptible, less than or equal to 4 ug/mL; intermediate, 8-16 ug/mL; and resistant, greater than or equal to 32 ug/mL) (2). The VISA isolate was susceptible to rifampin, chloramphenicol, trimethoprim-sulfamethoxazole, and tetracycline. The patient is continuing to receive antimicrobial therapy. Epidemiologic and laboratory investigations are under way to assess the risk for person-to-person transmission of VISA and to determine the mechanism(s) by which these strains develop resistance.

Reported by: R Martin, DrPH, KR Wilcox, MD, State Epidemiologist, Michigan Dept of Community Health. Div of Applied Public Health Training (proposed), Epidemiology Program Office; Hospital Infections Program, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Since the 1980s, when MRSA emerged in the United States, vancomycin has been the last uniformly effective antimicrobial available for treatment of serious S. aureus infections. This report documents the emergence of VISA in the United States and may signal the eventual emergence of S. aureus strains with full resistance to vancomycin. Widespread use of antimicrobials, such as vancomycin, is a major contributing factor for the emergence of vancomycin-resistant organisms, including vancomycin-resistant enterococci.

To accurately detect staphylococci with reduced susceptibility to vancomycin, antimicrobial susceptibility should be determined with a quantitative method (broth dilution, agar dilution, or agar gradient diffusion) using a full 24 hours of incubation at 95 F (35 C). Strains of staphylococci with vancomycin MICs of 8 ug/mL were not detected using disk-diffusion procedures.

To prevent the spread of these organisms within and between facilities, health-care providers and facilities are advised to 1) ensure the appropriate use of vancomycin (3); 2) educate those personnel who provide direct patient care about the epidemiologic implications of such strains and the infection-control precautions necessary for containment; 3) strictly adhere to and monitor compliance with contact isolation precautions and other recommended infection-control practices, and 4) conduct surveillance to monitor the emergence of resistant strains. Detailed recommendations for the prevention, detection, and control of S. aureus strains with reduced susceptibility to vancomycin are outlined in "Interim Guidelines for Prevention and Control of Staphylococcal Infection Associated with Reduced Susceptibility to Vancomycin," published previously in MMWR (4).

The isolation of S. aureus with confirmed or "presumptive" reduced vancomycin susceptibility should be reported through state and local health departments to CDC's Investigation and Prevention Branch, Hospital Infections Program, National Center for Infectious Diseases, Mailstop E69, 1600 Clifton Road, NE, Atlanta, GA 30333; telephone (404) 639-6413. Physicians treating patients with infections caused by staphylococci with reduced susceptibility to vancomycin can obtain information about investigational drug therapies from the Food and Drug Administration's Division of Anti-Infective Drug Products, telephone (301) 827-2120.

References

1. CDC. Reduced susceptibility of Staphylococcus aureus to vancomycin -- Japan, 1996. MMWR 1997;46:624-6.

2. National Committee for Clinical Laboratory Standards. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically -- fourth edition: approved standard, M7-A4. Villanova, Pennsylvania: National Committee for Clinical Laboratory Standards, 1997.

3. CDC. Recommendations for preventing the spread of vancomycin resistance: recommendations of the Hospital Infection Control Practices Advisory Committee (HICPAC). MMWR 1995; 44(no. RR-12).

4. CDC. Interim guidelines for prevention and control of staphylococcal infection associated with reduced susceptibility to vancomycin. MMWR 1997;46:626-8,635.

   
   

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