Are we closer to a rapid test for Ebola?
In the early stages of infection, it's easy to mistake Ebola for other diseases, and sorting out which patients carry the virus is a delicate and dangerous task. Happily, there's new evidence that a simple test from Corgenix, a company based in Colorado, could make that job a lot easier.
It looks like a pregnancy test, gives results in 15 minutes and works just as well as the current gold-standard method for detecting Ebola – at least in the two Sierra Leone clinics where it was tested this past February. An analysis of this test was published on Thursday in the medical journal, The Lancet.
For more on the challenges of diagnosing Ebola, check out science correspondent Miles O'Brien's report from Sierra Leone:
The current method of checking for Ebola involves a test called PCR, short for polymerase chain reaction, which looks for the virus' genetic material. While PCR is well established, it calls for expensive, carefully calibrated machinery and experienced technicians. The test itself takes several hours to run, and a bigger problem is the scarcity of equipment and trained lab personnel in Sierra Leone and other West African countries. Since late last year, foreign governments and aid groups have eased the crisis by setting up a number of mobile laboratories, but it still often takes days to get results. Blood samples must be packaged, transported (usually on motorbikes) and then unsealed before the test can be run. Careful safety precautions are required at every step. On top of that, there are frequent delays in communicating results back to the clinic or hospital where the unfortunate patient waits.
The new study compared PCR to the Corgenix rapid test, in which a drop of blood from a pricked finger is prepared and dropped onto a paper strip. If a specific protein from the Ebola virus is present, it is captured by antibodies that are infused into the paper; gold nanoparticles on the resulting combination produce a reddish stripe.
In the two clinics where the trial was run, suspected Ebola patients gave blood that was tested by both methods, although doctors weren't told of the rapid test results, so they wouldn't influence patient care. As it turned out, everyone who tested positive for Ebola via PCR also tested positive with the rapid test. On the flip side, both tests missed the same proportion of cases – about 1 in 12 – as determined by subsequent re-testing in a more controlled environment.
The takeaway, according to Dr. Nira Pollock, who oversaw the study for the Boston-based group Partners in Health, is that the Corgenix test works "very well," but only in people who are already showing symptoms and have a high level of virus in their blood.
"It clearly can't be used on people who are asymptomatic," says Pollock, the Associate Medical Director of the Infectious Diseases Diagnostic Laboratory at Boston Children's Hospital. "People really want an ultra-sensitive fingerstick test, but that hasn't been developed yet."
Earlier this spring, Dr. Thomas Frieden, Director of the U.S. Centers for Disease Control and Prevention, said a rapid test could be especially useful in determining whether a person who died was a victim of Ebola, to flag whether family members and caregivers were at risk.
Others say the test could be extremely valuable when doctors are concerned about Ebola, but have no time to wait for test results. A sick woman giving birth, for example.
"If a woman presents in labor, or there's an emergency like a trauma case, a rapid result is really key in determining how to handle the patient," says Dr. Jana Broadhurst, the Lancet paper's lead author. "That's the most likely scenario for this, sooner than later."