MRSA’s bold move has CDC gathering its forces

Community outbreaks, VRSA make bug a priority

Admittedly distracted by bioterrorism, public health officials are marshalling their forces to do battle with an old foe before it gets completely out of its cage. Methicillin-resistant Staphylococcus aureus (MRSA) is in the news too much for anyone’s good, spreading through communities and mutating into full-blown vancomycin-resistant S. aureus (VRSA).

"Once we are stabilized with bioterrorism, we want to have a major push on MRSA," says Steve Solomon, MD, acting director of the division of healthcare quality promotion at the Centers for Disease Control and Prevention (CDC).

"The two areas of interest that have pushed it, if you will, on the other side of the tipping point are certainly VRSA from last summer and what appears to be an increasing incidence of MRSA beyond health care venues. The recent episode in the jail in Los Angeles County got a lot of people interested, and there have been other smaller outbreaks and clusters in the community." (See Hospital Infection Control, March 2003 under archives at www.HIConline. com)

Currently the CDC is working with four states in a project to define the spectrum of disease, determine populations affected, and develop studies to define who is at particular risk for infection with MRSA.

The agency is working with state health departments to assist in the development of surveillance systems for tracking MRSA in the community. CDC laboratories also are working to characterize the unique features of MRSA strains from the community.

A potentially greater concern is that a once theoretical superbug became a reality last year — twice. In separate incidents last year, a case of VRSA occurred in the United States due to transfer of resistance genes from vancomycin-resistant enterococci.

The mechanism of resistance in both cases was a "conjugation event": a 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.

"The best way to solve the VRSA problem is to prevent MRSA," Solomon recently told members of the CDC’s Healthcare Infection Control Practices Advisory Committee (HICPAC). "And the best way to beat MRSA is to prevent health care-associated infections."

But there is not even agreement on the best way to do that. The CDC’s HICPAC committee is working on its fifth draft version of new infection control guidance for multidrug-resistant organisms such as MRSA.

One of the key areas of contention is the issue of recommending active surveillance cultures to detect colonized and infected patients. Advocates of this practice argue the drug-resistance problem will never be solved unless patients who are colonized or infected with MRSA can be identified and placed in contact isolation rather than serving as an undetected reservoir to spread the pathogen to other patients.

The current version of the HICPAC guideline recommends active surveillance cultures upon admission to high-risk areas but only as part of intensified interventions in the face of ongoing transmission.

"The struggle we are having is that we are trying to have recommendations that can be applied across the continuum of care," says Jane Siegel, MD, HICPAC member and professor of pediatrics at the University of Texas Southwestern Medical Center in Dallas.

"We have to separate out recommendations for acute care and for outside of acute care. We are still working with that," she adds.

Another draft infection control document under development by the Society for Healthcare Epi-demiology of America (SHEA) calls for more routine use of active surveillance. "The document basically supports use of aggressive surveillance not only in hospitals, but in all health care facilities," said James Steinberg, MD, a liaison HICPAC member representing SHEA. "They do make concessions that contact isolation could be modified in extended care facilities."

Public health officials would like to bring the CDC and SHEA documents into harmony, but it remains unclear if that is going to happen. How-ever, the recent reports of MRSA in the community and the rise of VRSA may pressure the CDC to move to more strenuous guidelines.

A long-time scourge of hospitals, MRSA seems to be arising in the community through a variety of means. A recently published meta-analysis by researchers at the University of Virginia in Charlottesville found that MRSA colonization can persist for months to years.1

The majority of colonized patients remain completely asymptomatic. Thus acquisition of MRSA, whether it occurs in the hospital or in the community, typically goes unnoticed unless clinical infection develops. In addition to these latent cases, MRSA can occur in the community through transfer of the MecA gene, which confers drug-resistance capabilities to susceptible staph strains.

The evolving epidemiology of MRSA could be compared with what has been described for penicillin-resistant S. aureus, the UVA researchers noted. Penicillin was introduced in 1941, and resistant S. aureus strains appeared in 1944.

"Initially, these resistant strains were associated with nosocomial infections, but dissemination into the community subsequently followed, seemingly, at a time when the rate of penicillin resistance among hospital patients with staphylococcal infections approached 50%," they warned.

MRSA currently accounts for about half of all staph infections. The "tipping point," to use Solomon’s term, appears to be at hand.

Reference

1. Salgado CD, Farr BM, Calfee DP. Community-acquired methicillin-resistant Staphylococcus aureus: A meta-analysis of prevalence and risk factors. Clin Infect Dis 2003; 36:131-139.