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Update: Staphylococcus aureus with reduced susceptibility to vancomycin -- United States, 1997

Morb Mort Weekly Rep (Sep) 46:No.35 1997

Reproduced from MMWR:

Update: 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 infection worldwide. Since the emergence of methicillin-resistant S. aureus (MRSA) in the 1980s in the United States, vancomycin has been the antimicrobial agent of choice for serious MRSA infections. S. aureus with reduced susceptibility to vancomycin (minimum inhibitory concentration [MIC]=8 u/mL) was first reported to have caused infection in a patient in Japan in May 1996 (1). In August 1997, the first S. aureus isolate intermediately resistant to vancomycin (VISA; MIC=8 u/mL) in the United States was reported in Michigan (2). This report updates the ongoing investigation in Michigan and describes preliminary findings of the ongoing investigation of a second case of VISA infection in a patient in New Jersey.

Case 1.
In July 1997, VISA-associated peritonitis was diagnosed in a Michigan resident who was being treated with long-term ambulatory peritoneal dialysis (2). During January-June, the patient had been treated with multiple courses of both intraperitoneal and intravenous vancomycin for repeated episodes of vancomycin-susceptible, MRSA-associated peritonitis. Although intermediately resistant to vancomycin, the VISA isolate was susceptible to chloramphenicol, rifampin, trimethoprim-sulfamethoxazole, and tetracycline. The patient continues to receive antimicrobial therapy at home. As a part of the investigation, cultures were obtained from the hands and nares of the index patient's household contacts, hospital roommates, and health-care providers. Although S. aureus was isolated from 13 (25.4%) of 51 hand cultures and eight (15.6%) of 51 nares cultures, none of these cultures were positive for VISA.

Case 2.
In August 1997, a VISA-associated bloodstream infection was diagnosed in a New Jersey resident with long-term MRSA colonization and repeated MRSA infections since February. The patient was not receiving chronic dialysis. In addition, since February, the patient has had vancomycin-resistant enterococcal (VRE) colonization. During March-August, the patient had been treated with multiple courses of vancomycin for repeated MRSA bloodstream infections. In August, a blood culture from the patient grew an MRSA strain with intermediate resistance to vancomycin (MIC=8 u/mL); all previous MRSA strains had been vancomycin susceptible. This VISA isolate was sent to CDC, where the intermediate resistance was confirmed; the isolate was susceptible to gentamicin, trimethoprim-sulfamethoxazole, tetracycline, and imipenem. The patient continues to receive antimicrobial therapy at home.

Reported by: R Martin, DrPH, KR Wilcox, MD, State Epidemiologist, Michigan Dept of Community Health. C Campbell, DVM, H Ellis, MD, State Epidemiologist, New Jersey Dept of Health and Senior Svcs. Div of Applied Public Health Training (proposed), Epidemiology Program Office; Hospital Infections Program, National Center for Infectious Diseases, CDC.

Editorial Note:
Since the 1980s (when MRSA emerged in the United States), vancomycin has been the last uniformly effective antimicrobial available for treatming serious S. aureus infections. The findings in this report document two VISA infections in the United States within a 1-month period. Widespread use of antimicrobials, such as vancomycin, is a major contributing factor for the emergence of VRE and other vancomycin-resistant organisms. In the first case in the United States (case 1), spread of VISA to other patients and health-care workers probably was prevented by prompt identification of the isolate and its susceptibility pattern, isolation of the patient while hospitalized, and implementation of recommended infection-control practices (3). In both Michigan and New Jersey, VISA was detected by using a 24-hour MIC dilutional method that had not changed over the period during which these patients had repeated S. aureus infections. The detection of a second U.S. strain of VISA with a different antimicrobial susceptibility pattern from those isolated previously suggests that these strains are developing de novo secondary to vancomycin exposure. Further studies are under way to determine VISA genotypes and to identify the mechanism(s) of resistance.

The emergence of VISA in the United States suggests that S. aureus strains with full resistance to vancomycin may eventually emerge. These episodes emphasize the need to enhance laboratory capacity at the hospital and state levels to recognize these strains, the importance of prudent use of antimicrobials, and the requirement for full implementation of recommended infection-control measures to prevent transmission of these strains. To prevent spread of these organisms within and between facilities, health-care providers and facilities are advised to 1) use a quantitative method (broth dilution, agar dilution, or agar gradient diffusion) to identify these strains; 2) ensure appropriate use of vancomycin, including the review of antibiograms for alternative antibiotics (4); 3) educate health-care personnel about the epidemiologic implications of emergence of such strains and the appropriate infection-control precautions necessary to prevent their spread; 4) strictly adhere to and monitor compliance with contact-isolation precautions and other recommended infection-control practices; and 5) conduct surveillance to monitor for the emergence of resistant strains. Detailed recommendations to prevent, detect, and control S. aureus with reduced susceptibility to vancomycin have been published (3).

The isolation of S. aureus with confirmed or "presumptive" reduced vancomycin susceptibility should be reported immediately through state and local health departments to CDC's Investigation and Prevention Branch, Hospital Infections Program, National Center for Infectious Diseases, Mailstop E-69, 1600 Clifton Road, N.E., 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, Center for Drug Evaluation and Research, telephone (301) 827-2120.

References

1. CDC. Reduced susceptibility of Staphylococcus aureus to vancomycin--Japan, 1996. MMWR 1997;46:624-4.

2. CDC. Staphylococcus aureus with reduced susceptibility to vancomycin--United States, 1997. MMWR 1997;46:765-6.

3. CDC. Interim guideline for prevention and control of staphylococcal infection associated with reduced susceptibility to vancomycin. MMWR 1997;46:626-8,635-6.

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

Erratum: Vol. 46, No. 35

In the article, Staphylococcus aureus with Reduced Susceptibility to Vancomycin--United States, 1997," an error appears in the second sentence of the second paragraph. The sentence should read, "During January-June 1997, the patient had been treated ..."