Blood Test May Catch Deadly Fungal Infection Quickly
Test for Candida in bloodstream is not yet on market
Wednesday, April 24, 2013
The test, which is not yet on the market, looks for Candida infection in the blood. The fungus is best known for causing common vaginal yeast infections, but when it gets into the bloodstream it can cause serious infections of organs and tissue throughout the body.
Candida blood infections -- known as candidemia -- are very rare in healthy people, but they are the fourth most common type of blood infection among U.S. hospital patients, according to the U.S. Centers for Disease Control and Prevention.
The infection is typically transmitted through contaminated catheters, and seen in seriously ill patients -- such as those in the intensive care unit, or with weakened immune systems.
The symptoms of candidemia are vague, and include fever and chills, so doctors use blood cultures to diagnose it. That means putting a blood sample in a special broth that feeds the yeast organism until it grows enough to be detected.
But Candida "is a slow grower," and it takes a few days to get blood culture results back, said Thomas Lowery of T2 Biosystems, the Lexington, Mass.-based company developing the new test.
By that time, it may be too late for the patient. About 40 percent of people with Candida blood infections die, and delayed diagnosis bears part of the blame, Lowery and his colleagues write in the April 24 issue of the journal Science Translational Medicine.
Getting a precise diagnosis is vital, Lowery said, both to confirm that it's Candida, and to pinpoint which type it is. "You need to know the specific Candida so you can use the right antifungal drug," he said.
In the new study, Lowery's team found that the test they've developed can reliably detect the five most common species of Candida within about three hours.
The researchers used blood samples from healthy people and "spiked" them with Candida yeast. They then analyzed the samples with the new test and with standard blood cultures. The two tests were in agreement on "positives" 98 percent of the time.
An expert not involved in the research said the test's sensitivity is "very, very good."
"This is preliminary, but the technology looks extremely promising," said Christine Ginocchio, chief of infectious disease diagnostics at North Shore-LIJ Health System in Lake Success, N.Y.
What's particularly "exciting" is that the technology could potentially be used to test for other pathogens that cause serious bloodstream infections, according to Ginocchio, who is also a member of the Infectious Diseases Society of America's Diagnostics Task Force.
Ideally, Ginocchio explained, when doctors suspect a patient has a bloodstream infection, they would be able to take a blood sample, directly test it, then have a result in a few hours. The problem right now is that a blood sample would normally not contain enough of the culprit bug -- be it a fungus or bacterium -- to detect.
Plus, Ginocchio noted, the blood contains a lot of other genetic material that gets in the way of spotting that bit of foreign-invader DNA. That's why blood cultures are done.
The new test, which is based on so-called magnetic resonance technology, essentially removes the "noise" coming from other material in the blood sample, allowing it to zero in on the pathogen.
There is still more work to be done. "Now you'd like to see this tested in a larger, multicenter trial," Ginocchio said.
The process would also need to be automated, she noted, to be feasible for smaller community hospitals. T2 Biosystems' Lowery said the researchers are working on making the method "fully automated."
Exactly what it would all cost is not known. But both Ginocchio and Lowery said that if the test gets more patients on the right drug quickly, the cost would likely be worth it.
According to Lowery's team, research suggests that with Candida infections, starting the right antifungal drug within 12 hours can cut the death rate from 40 percent to 11 percent.
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