MRSA's Threat Continues

It has become deadlier than AIDS. According to a recent report from the CDC, more people in the U.S. now die from methicillin-resistant Staphylococcus aureus (MRSA) than from the long-feared virus.

The report also revealed MRSA was responsible for an estimated 94,000 life-threatening infections and 18,650 deaths in 2005.¹ That same year, roughly 16,000 people in this country died from AIDS, cite CDC figures. The national estimate is more than double the invasive MRSA prevalence reported by CDC researchers 5 years earlier.¹

MRSA - first reported in the early 1960s - is now regarded as a major hospital-acquired pathogen worldwide. Nearly 35 percent of U.S. hospital strains of are resistant to methicillin or other penicillin antibiotics, and in recent years the emergence of vancomycin-resistant S. aureus (VRSA) has caused additional concern.²

Fortunately, the scientific community now has a better idea of MRSA prevalence rates.

"Until recently, we could only speculate about the number of cases occurring within and outside healthcare settings," said Mary Beth Minyard, MSCLS, M(ASCP), associate project leader, Microbiology, Southern Research Institute, Birmingham, AL. "The reality is that MRSA has steadily increased within our hospitals and nursing homes and is spreading into the community at an alarming rate."

Root Of The Problem
MRSA infections are becoming increasingly common. Some experts contend overuse and misuse of antibiotics by the public and prescribing physicians have created the problem.

Another contributing factor is personal sanitation and a fundamental failure to recognize the characteristics of the infectious process.

"The biggest contributor to the rise in MRSA cases is poor infection control and sanitation practices," declares James W. Snyder, PhD, D(ABMM), professor of Pathology, director, Microbiology, Department of Pathology and Laboratory Medicine, University of Louisville Hospital.

As a result, resistance has spread out of healthcare settings and into the community.

"Until recent years, MRSA has been overlooked and not addressed adequately, so healthcare settings have inadequate isolation procedures and guidelines in place," adds Minyard.

Healthcare Versus Community
There once were distinct differences between the nosocomial (HA-MRSA) and community acquired strains (CA-MRSA); however, CA-MRSA strains are now being transmitted within the hospital setting, say experts.

This presents a looming problem because CA-MRSA genes responsible for encoding resistance are more readily transferred to other S. aureus strains than genes from the typical nosocomial genotypes, says Minyard.

"This will potentially result in higher MRSA rates within our healthcare settings, which will ultimately result in higher infection rates and increased hospital stays and costs," she continued. "As well, CA-MRSA strains have the potential to cause more severe infections due to certain virulence characteristics."

Valid Identification
The clinical laboratory plays a critical role in determining susceptibility and diagnosing the particular type of MRSA. Antimicrobial susceptibility testing is mainly based on the method recommended by the Clinical and Laboratory Standards Institute (CLSI). A positive beta-lactamase test will indicate resistance to penicillin, while resistance to other antimicrobials, including methicillin, is usually tested using the disk diffusion test.³

Traditional MRSA screening is performed via plate-based methods. Surveys suggest this methodology group accounts for more than 90 percent of the screening tests performed.²

But isolation from screening swabs can be a lengthy procedure due to the number of contaminating organisms present in swabs from nonsterile sites.² Thus, an increasing number of surrogate methods - including chromogenic media, rapid screening kits, molecular assays and automated systems - are making their way into the clinical laboratory.²

Molecular Movement
While some say the most common method of MRSA detection - the culture - is a bit archaic, it remains the gold standard. The recent escalation in MRSA cases, however, is perhaps a strong indicator of a clear-cut need for faster, more accurate detection methodologies.

"There needs to be a more rapid and reliable method of detection, specifically to reduce turnaround time," Snyder concurs.

The culture is being supplemented - and perhaps groomed for replacement - by technique known as polymerase chain reaction (PCR) detection. The advantage of PCR is that it affords direct detection and is not dependent on a culture, allowing detection within 2 hours versus the overnight to 2-day timeframe of a culture.

Such molecular technologies will help determine which individuals need therapy, then streamline or plan that therapy on a personal basis. But the therapy, according to Snyder, is going to be a combination of antibiotics and whether the individual should be decolonized.

"You are reducing the time to detection, and by doing so you have identified the patient that needs the attention," he said. "But, ultimately, the clinician has to determine if he is dealing with an infectious process that requires further antibiotic therapy or a situation where the patient is colonized with the organism, which still indicates the need for the good practice of containment procedures."