Rapid MRSA test gets FDA OK

As incidence rates increase, infectious disease and public health experts praise decreases in the time needed to detect these bacteria.

By Victoria Stagg Elliott — Posted Jan. 28, 2008

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Those working to control the spread of methicillin-resistant Staphylococcus aureus say this task is about to get easier. In January, the Food and Drug Administration approved the first blood test that can differentiate it from the methicillin-susceptible variant in two hours, rather than the 24 to 48 hours or longer that currently available technology takes.

"[This] test is good news for the public health community," said Daniel G. Schultz, MD, director of the FDA's Center for Devices and Radiological Health.

The BD GeneOhm StaphSR Assay assesses a blood sample for genetic material specific to the two main forms of these bacteria. Studies leading to the test's approval found that it could identify 100% of MRSA samples and 98% of the susceptible types. According to an FDA statement, this test should be used in patients already suspected of having a staph infection but not to monitor treatment or initially detect it. Doctors still might have to conduct follow-up testing to pin down precisely what will kill particular bacteria, but physicians say the information provided by this product will be enough to narrow down treatment choices early on.

"Compared to what we have now, this is terrific. It's enough information to get you started," said Ed Septimus, MD, a board member of the Infectious Diseases Society of America.

Physicians expect to use it to identify more quickly which antibiotic is most likely to work and which patients need to be isolated from others. Experts hope that this will interrupt MRSA's spread and reduce the use of broad spectrum antibiotics. In turn, this may slow the development of more resistant organisms.

"We will be able to get appropriate treatment to the patient much faster, and we will be able to intervene at a much earlier time so transmission does not occur," said Dr. Septimus, also an infectious disease physician in Houston.

Initially, this test most likely will be used on the sickest, hospitalized patients but also may trickle down to other practice settings for less-critical infections. MRSA has long been a problem in the health care setting, but it is increasingly a community problem as well.

This test previously was given FDA approval to identify colonized patients.

The product's manufacturer, BD (Becton, Dickinson and Co.), is pursuing U.S. approvals for it to be used for nasal swabbing and the detection of MRSA in wounds. These versions were launched in Europe at the end of 2007.

But although there is a lot of hope for the test's potential, there are also concerns. Experts, for instance, expect there may be a lag between this test becoming available and doctors becoming comfortable enough with it to use it for decision-making.

"Having more tools is good, but there's going to be a certain learning curve," said Thomas Fekete, MD, professor of medicine and an infectious disease specialist at Temple University in Philadelphia. "And I don't know if laboratories will be financially prepared to take on this new technology. I'm not saying it's not worth it, but there's a price to pay."

Experts say getting a better handle on MRSA is key, because evidence is accumulating that it may be far more common than previously thought.

A paper in the June 2005 Emerging Infectious Diseases suggested that MRSA could be found in 3.95 of every 1,000 hospitalized patients.

But a study in the December 2007 American Journal of Infection Control found that nationally, 46.3 per 1,000 inpatients carried the bacteria. Of these, at least 34 were infected and 12 were colonized. The remainder of cases were unclassified. Approximately 70% of cases appear to have been contracted in the health care setting.

The authors suspect that the true numbers may be much higher. Only 29% of institutions surveyed actively hunted for these bacteria, and most did not use highly sensitive means to do it.

"This is the minimum estimate, because the majority are not doing screening and [are] testing by less sensitive methods. It's a much bigger problem than anyone had predicted," said William Jarvis, MD, lead author on that paper and a consultant with Jason & Jarvis Associates, a private firm that provides expertise on public health, infection control and patient safety.

Other papers have documented MRSA's impact. One in the Oct. 17, 2007, Journal of the American Medical Association estimated that there were 94,360 cases of invasive MRSA infections and 18,650 deaths in 2005. Patients older than 65 were particularly vulnerable.

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The wide reach of MRSA

[download pdf]

Methicillin-resistant Staphylococcus aureus may be far more common in hospitals than previously thought. Researchers asked infection-control officers to report MRSA cases for one day in fall 2006. Previous data suggested a national infection rate of 3.95 per 1,000 patients, but this survey found 46.3 per 1,000.

MRSA patients
per 1,000
Alabama 52.9
Alaska 36.7
Arizona 39.6
Arkansas 57.9
California 45.9
Colorado 39.1
Connecticut 37.9
Delaware 79.8
District of Columbia 12.3
Florida 55.3
Georgia 44.6
Hawaii 91.0
Idaho 25.7
Illinois 37.1
Indiana 42.7
Iowa 41.0
Kansas 48.2
Kentucky 32.9
Louisiana 33.0
Maine 68.7
Maryland 53.8
Massachusetts 59.0
Michigan 49.2
Minnesota 30.7
Mississippi 16.3
Missouri 47.8
Montana 25.9
Nebraska 59.6
Nevada 37.8
New Hampshire 60.9
New Jersey 30.2
New Mexico 26.0
New York 63.5
North Carolina 58.3
North Dakota 23.5
Ohio 37.5
Oklahoma 48.1
Oregon 36.6
Pennsylvania 56.0
Rhode Island 83.5
South Carolina 64.8
South Dakota 0.0
Tennessee 59.8
Texas 41.4
Utah 21.9
Vermont 46.5
Virginia 39.6
Washington 36.1
West Virginia 51.8
Wisconsin 39.3
Wyoming 10.0

Source: American Journal of Infection Control, December 2007

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External links

"National prevalence of methicillin-resistant Staphylococcus aureus in inpatients at U.S. health care facilities, 2006," abstract, American Journal of Infection Control, December 2007 (link)

Centers for Disease Control and Prevention on health care-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) (link)

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