VRSA arises again with genetic transfer from VRE
CDC warns other cases are likely to occur
For the second time this year, a case of vancomycin-resistant Staphylococcus aureus (VRSA) has occurred in the United States due to transfer of resistance genes from vancomycin-resistant enterococci, the Centers for Disease Control and Prevention (CDC) reports.1 The case in Pennsylvania follows a previous report in Michigan of the first confirmed case of VRSA, suggesting that long-feared superbug is beginning to emerge as new ominous drug-resistant pathogen.2 (See Hospital Infection Control, August 2002, under archives at www.HIConline.com.)
The mechanism of resistance in both cases this year has been a "conjugation event": genetic transfer from VRE to MRSA. The vancomycin-resistance determinant vanA, typically found in VRE but never in a clinical staph strain, was found in the VRSA isolates in both cases. Researchers in England proved such a genetic transfer could occur a decade ago in controversial laboratory studies that produced a fully resistant strain in vitro.3
"Development of this VRSA appears to be unrelated to the previous VRSA identified in Michigan," the CDC states. "However, because both were probably the result of conjugation events, additional VRSA infections are likely to occur. . . . The presence of vanA in this VRSA suggests that the resistance determinate was acquired from a vancomycin-resistant enterococcus. Therefore, clinical microbiology laboratories must ensure that they are using susceptibility testing methods that will detect VRSA and that they are saving potential VRSA for confirmatory testing."
Similar to the Michigan patient, the second VRSA patient had chronic foot ulcers. The patient was admitted to a hospital in Pennsylvania and evaluated for a chronic foot ulcer and possible osteomyelitis on Sept 20, 2002. An infecting isolate was forwarded to CDC, where it was confirmed to be VRSA (vancomycin MIC=32 mcg/mL by broth microdilution testing). The isolate contained both the mecA and vanA genes mediating oxacillin and vancomycin resistance, respectively.
The isolate was susceptible to chloramphenicol, linezolid, minocycline, quinupristin-dalfopristin, rifampin, and trimethoprim-sulfamethoxazole. The patient has been discharged from the hospital and is responding to antimicrobial treatment. The patient is receiving home health care. The CDC is assisting health care providers investigating the case of VRSA.
"The goals of this investigation include assessment of infection control practices in the hospital and home setting and the possibility of transmission of the organism to other patients, health care providers, and family or social contacts," the CDC reports. "Previous investigations of VRSA and vancomycin-intermediate S. aureus in the home setting demonstrated no transmission among family or home health care contacts."
The CDC recommends contact precautions when caring for patients with VRSA infections. That includes placing the patient in a private room, wearing gloves and a gown during patient contact, washing hands after contact with the patient and infectious body tissues or fluids, and not sharing patient-care items with other patients. For guidelines on preventing spread of VRSA, go to www. cdc.gov/ncidod/hip/10_20.pdf. Isolation of S. aureus with confirmed or "presumptive" vancomycin resistance should be saved and reported via state and local health departments to CDC’s Division of Healthcare Quality Promotion, National Center for Infectious Diseases at (800) 893-0485.
References
1. Centers for Disease Control and Prevention. Public health dispatch: Vancomycin-resistant Staphylococcus aureus — Pennsylvania, 2002. MMWR 2002; 51:902.
2. Centers for Disease Control and Prevention. Staphylo- coccus aureus resistant to vancomycin, United States, 2002. MMWR 2002; 51:565-567.
3. Noble WC, Virani Z, Cree RG. Co-transfer of vancomycin and other resistance genes from Enterococcus faecalis NCTC 12201 to Staphylococcus aureus. FEMS Microbiol Lett 1992; 93:195-198.