Second VISA case appears as bloodstream infection

Following rapidly on the heels of the first U.S. case of vancomycin intermediate-resistant Staphylococcus aureus (VISA) infection in Michigan, a second case of VISA infection has occurred in a patient in New Jersey, the Centers for Disease Control and Prevention reports.1,2

While the location of the Michigan case has not been released, Our Lady of Lourdes Medical Center in Camden, NJ, confirmed that the second patient was treated there. While emphasizing that both the privacy of the patient and family will be protected, the medical center released a brief statement that noted in part: "One community member who was already infected with S. aureus presented to the hospital. Suspicion of the presence of this organism was raised as a result of [our] standard microbiology protocols. . . . The patient has been successfully treated and shows no further signs of S. aureus infection. . . . Patients, staff and visitors are at no risk for contracting this organism through contact with the hospital or its workers. As always, [our] staff will continue to practice standard precautions to protect our patients and themselves from all types of exposure."

According to the CDC report on the case, in August 1997 a VISA-associated bloodstream infection was diagnosed in a patient who had long-term methicillin-resistant S. aureus (MRSA) colonization and repeated MRSA infections since February. The patient was ot receiving chronic dialysis like the first U.S. case, but had undergone a similar pattern of intermittent exposure to vancomycin. In addition, since February, the patient has had vancomycin-resistant enterococcal (VRE) colonization. From March to August of 1997, the patient had been treated with multiple courses of vancomycin for repeated MRSA bloodstream infections. A blood culture from the patient grew an MRSA strain with intermediate resistance to vancomycin, with a minimum inhibitory concentration of 8. The New Jersey patient continues to receive antimicrobial therapy at home. Though few additional details were released on the case, the CDC did confirm that an investigation is under way to determine if any additional transmission occurred.

"This patient is primarily an outpatient, but has been hospitalized for MRSA infections, particularly since some of the MRSA infections were bloodstream infections," says Michelle Pearson, MD, medical epidemiologist in the CDC hospital infections branch. "Similar to the case in Michigan — because the [New Jersey] patient was known to have MRSA and VRE — the patient had been placed on isolation precautions. We don’t have any preliminary evidence to suggest that any transmission has occurred."

The VISA isolate was sent to the CDC, where intermediate resistance to vancomycin was confirmed and drug susceptibility was found to gentamicin, trimethoprim-sulfamethoxazole, and tetracycline. The Michigan VISA strain was susceptible to four drugs — including trimethoprim-sulfamethoxazole and tetracycline — but there is some question of whether the susceptibility pattern had much clinical value. (See related story on the Michigan case, p. 145.) The CDC recommends that clinicians determine such susceptibility patterns. However, despite the two VISA cases, the agency has not yet recommended that patients with long-term MRSA infection undergoing vancomycin therapy be routinely reassessed for possible treatment with other antimicrobials.

"[Clinicians] may have been able to use some of those other drugs, either alone or perhaps in combination with lower doses of vancomycin," Pearson says. "It is very difficult to say how those antibiograms may translate to clinical response. It is a message to health care providers that there may be some utility to examining the antibiograms and looking at alternative therapies to vancomycin."

References

1. Centers for Disease Control and Prevention. Staphylococcus aureus with reduced susceptibility to vancomycin — United States, 1997. MMWR 1997; 46:765-766.

2. Centers for Disease Control and Prevention. Update: Staphylococcus aureus with reduced susceptibility to vancomycin — United States, 1997. MMWR 1997; 46:813-814.