As the Ebola outbreak simmers on in West Africa, researchers have shown the utility of a rapid test for the virus that could help contain another epidemic. The ReEBOV test, which needs only a fingerprick of blood and gives results in about 15 minutes, was granted Emergency Use Authorization by the World Health Organization (WHO) in February, based on laboratory assessments. Now, data collected from ReEBOV’s use on the ground in Africa have added further evidence of its accuracy.
“This is an important proof-of-principle that the test can really be used in a field setting,” says infectious disease doctor Charles Chiu of the University of California, San Francisco, who was not involved in the study.
Throughout the recent Ebola outbreak, clinicians have relied on PCR-based tests to diagnose cases of the viral disease. The tests require a full vial of blood to be drawn from a patient’s arm and transported to the nearest laboratory facility—which can take hours or days. In the lab, over the course of several hours, a PCR machine amplifies the genetic material in the blood until there is a sufficient amount to detect. In all, the process can take a few days—during which time a patient suspected of carrying Ebola must be quarantined or housed in holding units where they are at risk of infection—and costs about $100, according to WHO.
The newer ReEBOV test, currently manufactured by Colorado-based Corgenix, is like the fingerprick tests used by diabetics to test their blood sugar. Within a few minutes after a drop of blood is placed on a paper strip, a line appears signaling a positive or negative result. Unlike PCR-based tests, which look for the presence of the virus’s genetic material, the ReEBOV test detects antigens: proteins made by the body in response to an Ebola infection. It’s estimated to cost about $15 per test and can easily be performed under tough field conditions.
Over a 2-week span in February, researchers used both the ReEBOV test and a classic PCR-based test on 106 patients who showed up at two clinics in Sierra Leone with suspected Ebola symptoms. In addition, the scientists compared the tests’ performances on 284 previously collected blood samples. The ReEBOV antigen test detected every case of Ebola that was diagnosed using the slower PCR-based test, giving it what the researchers believed was a sensitivity of 100%, they report online today in The Lancet. The test also had a handful of false positives, however, making its specificity 92%.
“We were surprised by the performance,” says Nira Pollock, an infectious disease doctor at Boston Children’s Hospital and an author of the new study. “It was more sensitive than I expected for a rapid antigen diagnostic test.”
But Pollock admits the numbers may be misleading. After the collection of the initial data, the scientists used a second PCR-based test to look at some of the samples. The PCR test they’d been using as a “gold standard,” it turned out, wasn’t itself 100% sensitive, not only highlighting the discrepancy between different PCR-based tests but also casting doubts on their new results. In retrospect, “we think we probably overestimated the sensitivity and underestimated the specificity,” Pollock says. More data are needed to illuminate these numbers, she adds.
A fast, cheap, transportable Ebola test can’t come too soon, researchers say. “This test can be done in very austere environments, even off the back of a truck; it doesn’t require electricity or a sophisticated lab or an experienced technician,” points out Robert Garry, a virologist at Tulane University in New Orleans, Louisiana, who helped develop the technology the test is based on but was not involved in the new trial. “We need to be better prepared for the next Ebola outbreak and I think with this test we will be.”
“Having a rapid diagnostic test in the field would enable earlier identification of an Ebola outbreak,” Chiu adds. “And that could prevent further spread, especially in areas which really don’t have the resources to contain an outbreak.”
*The Ebola Files: Science and Science Translational Medicine have made a collection of research and news articles on the Ebola virus and the current outbreak freely available to researchers and the general public.