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Biomedicine

New Test Spots Infections in Hours, Rather than Days

A startup has developed a device that uses magnetic particles to identify pathogens rapidly.

A startup called T2 Biosystems is developing a test that uses magnetic nanoparticles to detect blood-borne infections in hours—compared to the days it now takes using conventional lab methods. The company’s first device—about the size of a printer—will target Candida, a fungus that is the third-most-common cause of hospital-acquired infections. The detection system can identify Candida in human blood samples in about two hours. Clinical trials involving samples from actual patients are in the works.

Faster test: This instrument can let doctors know if a deadly fungus is present in a blood sample in about two hours.

The sooner a hospital lab can identify the cause of a patient’s infection, the faster that patient can be put on the right antibiotics. Today, microbiologists often try to grow the infectious agent in the lab and run various tests to identify it. This can take a few days, and some organisms, including Candida, grow more slowly than others. Tests based on amplifying genetic material are considerably faster, but require complicated processing equipment. Tests that use fluorescent labels to light up a target are also faster, but samples like blood are too cloudy for the light to pass through.

T2 Biosystems’s technology is based on work carried out by researchers at MIT, Harvard, and Massachusetts General Hospital on tailoring iron-oxide nanoparticles to bind to specific biomarkers, and then using a miniature magnetic system to detect the binding. The detector is essentially a tiny, simplified version of a nuclear magnetic resonance imaging system. Such systems usually require very large, expensive magnets, whereas T2 Biosystems’s device uses a magnetic detector about the size of a penny.

Company founder and MIT materials science professor Michael Cima says there are two main advantages to the magnetic particle approach: magnetic fields can travel through blood and other media that light can’t penetrate, and the magnetic detection system is very sensitive—so it can tell clinicians precisely how much of a particular pathogen is present.

T2 Biosystems’s nanoparticle labels can also be tailored to detect a wide variety of pathogens, as well as cancer cells and other biomarkers, including hormones. The company chose to target the infectious fungus Candida for its first product because it sees rapid detection as an unmet need that could motivate hospitals to invest in the instrument. The company has not yet disclosed the price of the device, which it plans to launch in 2012.

In the United States, about 60,000 patients a year contract candidemia—meaning Candida is present in the blood—and about 40 percent of these patients die from it. Studies have shown that intervening in 12 hours instead of a few days reduces candidemia mortality rates to 11 percent, says T2 Biosystems CEO John McDonough. He hopes that intervening in the two hours it takes to perform a test with his company’s device might have an even greater benefit. In tests on blood spiked with Candida, the T2 detection system detected the fungus 95 percent of the time and with a 98 percent specificity.

Candida is a bad player if you have it in your blood,” says Philip Norris, associate director of the Blood Systems Research Institute at the University of California, San Francisco Medical Center. Infections tend to happen in patients who are already very sick, including those with compromised immune systems and people undergoing chemotherapy. While Norris says it will be necessary to wait for the results of the clinical trial,  large hospitals are likely to invest in the instrument “if it speeds up the diagnosis of really bad diseases like candidemia.”

T2 Biosystems has raised $30 million in venture funding so far, and is partnering with other companies working on biomarker tests that could be adapted for the magnetic-detection platform. The company will finalize the detection system this summer and will seek approval for the machinery and the Candida test from the U.S. Food and Drug Administration next year.

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