Martin Salia's friends in Sierra Leone celebrated when the doctor's Ebola test came back negative. But that celebration—in which friends hugged Salia—may have spread the disease to them, and Salia's belief in the negative finding may have cost him his life.
The test result, it turned out a few days later, was wrong. Salia died Monday at Nebraska Medical Center, in Omaha, after a desperate attempt to save his life.
His death shows the limitations of current Ebola testing, which takes time, money, electricity, and effort that is not practical in West Africa, where the needs are extraordinary and the infrastructure poor.
"What we want more than anything is a rapid diagnostic test to tell us if someone has Ebola right away, like you get a blood sugar reading from a drop of blood," said Winnie Romeril, a spokesperson for the World Health Organization in Sierra Leone.
The current gold-standard Ebola test can't detect the virus until 48-72 hours after symptoms first appear. Salia was probably tested too early the first time, and by the time he had a second test five days later, he was fighting for his life. It's also possible that the test itself was wrong, though that hasn't yet been determined.
Today's Ebola test is called PCR—for polymerase chain reaction—a Nobel Prize-winning method of analyzing genes in a blood sample. The same approach is used to screen for diseases like influenza, dengue, yellow fever, and HIV, the virus that causes AIDS.
PCR is reliable but can't detect low numbers of viruses. Plus, it requires electricity and running water, and tests take two to six hours and can cost upwards of $100. In Guinea, Liberia, and Sierra Leone, where the epidemic has raged since late last year—infecting more than 15,000 people and killing more than 5,400—poor roads and limited testing sites also slow results, the World Health Organization said in a Tuesday morning statement.
Although researchers are scrambling to develop faster, easier tests, the chances are slim that any will reach the market soon enough to help with the current epidemic.
Why Early Diagnosis Is So Difficult
Ebola copies itself exponentially: The first virus doubles, then that doubles and keeps doubling. So viral loads, the amount of virus in the bloodstream, stay low for the first few days and then almost literally explode.
Salia should have been retested within two to three days, and he and his caregivers should have assumed he might be infected despite the happy early test result, said Romeril, who is normally a flight paramedic in upstate New York.
So far during the outbreak, at least 129 health care workers in Sierra Leone have been infected and 100 have died, she said.
The high death rate among health care providers might reflect their professional culture, Romeril said, or simply that caregivers working 16-hour days are worn out and can't fight off the disease.
In Salia's case, there also might have been a mistake with the actual test, provided by the Chinese government.
"We don't know exactly how the Chinese assays work. We don't know enough about their instruments, their training," nor is there public information about many other countries' tests used in Africa, said Andrew Thompson, a senior analyst with GlobalData, a London-based business intelligence company for medical devices.
Across West Africa, various countries have provided laboratories, and they might all use different testing standards. In Sierra Leone, the U.S. government has built one major lab, Thompson said, and South Africa and China have each provided one mobile lab. The British recently arrived to set up a lab of their own.
The consequences of the current system are high.
A study published earlier this month in the New England Journal of Medicine found that quicker diagnostics could reduce deaths, because mortality rates are lower with early treatment.
"Lost time means that infected people may remain in the community, with a severe risk of unknowingly transmitting the virus to others," the WHO said in Tuesday's statement. What's more, the agency says, people who go to a hospital with malaria or other diseases with Ebola-like symptoms may be mistakenly held in Ebola centers and catch the disease there.
Finding a Faster, Cheaper Test
Researchers around the world are now racing to develop new technologies to diagnose Ebola faster, cheaper, more easily, with the same high level of accuracy, and—ideally—earlier in the disease.
Thompson, whose job it is to follow new technologies, says he's most excited about surface plasmon resonance, which involves measuring light as it reflects off the surface of a blood sample. Theoretically, he said, it could be used on a large scale and could produce results within minutes.
In early October, the WHO invited companies working on diagnostics to present their product's evidence; 16 did. Some of these products aim to be faster, or cheaper, or to detect Ebola with a simple finger prick instead of a full tube of blood.
Nanobiosym of Cambridge, Massachusetts, says its Gene-RADAR system can theoretically detect Ebola in under 30 minutes for under $20, within two to three days of infection.
In the short term, though, the most practical approach may simply be to tinker with PCR, Thompson said. Some companies have made useful advances, allowing chemicals to be stored at room temperature and tests to be done without heating and cooling samples, "ideal in countries where the power is not so reliable," he said.
"Most of the Western governments have spent a lot of money since 2001 on developing means to detect pathogens quickly," he said, but "there are always technical challenges and funding challenges."
So for the foreseeable future, PCR, imperfect as it is, remains the best available test.