Simple Test for Drug-Resistant Bacterium
A sensitive new diagnostic test for methicillin-resistant Staphylococcus aureus (MRSA)–a drug-resistant bacterium that can run rampant in hospitals–could help broaden access to fast, cheap testing. The test, being developed by Adnavance Technologies, a startup in San Diego, is simpler to perform than existing molecular diagnostics, potentially making it accessible to hospitals without sophisticated labs. Researchers hope that this will enhance surveillance efforts and help stem hospital-centered outbreaks.
MRSA, a variant of the bacterium that causes most staph infections, is commonly found in hospitals, where it can be passed between health-care workers and patients–often those with weak immune systems; it accounts for more than half of hospital-acquired infections in the United States. Not everyone who is infected with MRSA shows symptoms, making it difficult to determine who carries the potentially deadly bug.
In an effort to stop hospital outbreaks, a growing number of states require that hospitals test patients for MRSA before admitting them, or are considering legislation that would require them to do so. The entire Veterans Administration health system now requires patient screening, and the practice has been in place in Australia and some European countries for years.
To identify whether a patient is infected with MRSA, hospitals either culture bacteria collected from nasal and other samples, which can take several days, or perform newer molecular tests, which are much more expensive. Only about 35 percent of hospitals in the United States are certified to perform the newer type of testing. The others must send samples out for analysis, which can also take time. “If you’re going to isolate patients, the faster you can know who is colonized, the better,” says Phil Polgreen, director of the Infectious Disease Society of America’s Emerging Infections Network and an epidemiologist at the University of Iowa, in Iowa City. “With the culture studies, you don’t know a patient’s status for a few days. In that time, the infection could have spread.”
In states where hospital screening is required, patients must be quarantined until test results are in–a move that is both costly to hospitals and potentially dangerous for patients. Some studies also suggest that patients in isolation receive less attention from staff.
Adnavance is developing a new test that can detect MRSA bacteria directly, without requiring that the DNA be amplified, as is done in existing molecular tests. The central technology is a gold electrode coated with a proprietary marker that binds to the drug-resistant bacteria. As current flows through the electrode, it attracts negatively charged DNA, generating an easily detectable change in the surface charge of the electrode.
Randy White, Adnavance’s chief executive officer, says that in laboratory experiments, the test is 10 times more sensitive than existing tests, and it’s able to detect as few as 12,000 copies of bacterial DNA. He says that the company is now planning to test clinical samples from patients. Adnavance expects to launch the MRSA test in 2011, with an estimated price tag of $60 per test.
“It certainly sounds interesting,” says Carol Chenoweth, an epidemiologist at the University of Michigan Health System, in Ann Arbor. “But its success will depend on how well it functions in comparison to other tests out there, how much it costs, and how much technician time it requires to perform.”
Despite a growing interest in hospital surveillance, it’s not yet clear how effective patient testing is in reducing infection rates. Two conflicting studies were released last year: a large Swiss study found that surveillance had no effect, while a second U.S. study found that it significantly decreased infection rates. “I think the main benefit can be found in settings where there is outbreak occurring, either hospital-wide or in a unit,” says Daniel Diekema, a physician and epidemiologist who’s also at the University of Iowa. “Rapid tests provide an advantage in that setting because they give an answer in two to four hours, rather than 24 to 48 hours, during which time you’d have to decide whether to keep a patient isolated.”
If Adnavance can simplify the screening process even further, it may have a market among physicians’ offices. In addition to hospital-related strains, new strains of MRSA are emerging in community settings, such as gyms and day-care facilities. “The real mounting need is in the community,” says Stuart Levy, director of the Center for Adaptation Genetics and Drug Resistance at Tufts University School of Medicine, in Boston. “What you want is quick diagnostics you can do when you see the patient.”
But not everyone agrees that high-tech solutions are the best approach to controlling MRSA and other dangerous bugs that are springing up across the world. Diekema suggests that other drug-resistant bacteria are spreading more rapidly than MRSA, including strains of gram-negative bacteria, some of which can cause severe pneumonia. He says that simpler preventative measures that can stop the spread of all bacteria, such as increased hand washing, may be more effective.
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