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Companies ditch plans for rapid spit tests at home

The technology for rapid saliva-based coronavirus tests that could be used at home is not panning out the way some have hoped.

E25Bio and OraSure, two companies trying to develop rapid at-home coronavirus tests, have abandoned efforts to use saliva samples with their products. Instead, their tests, which detect pieces of coronavirus proteins called antigens, will rely for now on shallow nose swabs.

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Public health experts are eagerly watching the companies trying to develop the technology, which they hope will greatly expand the number of people who are tested. Some experts have even said that the rapid antigen tests, which are aimed at delivering a result in a matter of minutes, could perform as well as a vaccine in curbing the spread of the coronavirus and paving a path back to normalcy.

“If I was placing a bet — which I am, because I’m leading an antigen-based testing company — I would say it’s going to be very difficult for antigen-based testing to work on saliva samples,” said Bobby Brooke Herrera, chief executive of E25Bio and one of its founders. He said the notion that the virus sets up shop in the mouth and produces enough antigen there to be detected by today’s technology “is far-fetched.”

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As they continued to tinker with their tests, researchers at both E25Bio and OraSure found saliva’s performance to be more lackluster than anticipated, and were forced to pivot. One problem is that spit differs vastly from one person to another, and can even change over the course of a single day.

Both E25Bio and OraSure now plan to seek authorization from the Food and Drug Administration to sell at-home antigen tests using nose swabs, a technique similar to the one used by the much-talked-about Abbott antigen test that takes about 15 minutes.

The E25Bio test would require people to swab their nose, stir the sample into a chemical soup, apply the mixture to a paper strip and wait up to half an hour for bands to appear. E25Bio’s test picks up on about 80 percent of the infections that ultrasensitive laboratory tests detect — the F.D.A.'s bare minimum for a regulatory greenlight. OraSure declined to give any details about its test’s methodology or accuracy.

Saliva does seem to be working when used in laboratory tests known as P.C.R., which look for bits of the virus’s genetic material, or RNA, rather than antigens. P.C.R. tests detect minute amounts of coronavirus RNA, making them far more sensitive than antigen tests. Research teams at Rutgers and Yale have been granted emergency authorization for these spit P.C.R. tests.

At the University of Illinois, some 10,000 of the institution’s in-house P.C.R. tests are performed each day on saliva from students, faculty and staff members — roughly 1 percent of the nation’s daily tests.

Standard P.C.R. tests, however, take hours to run and are subject to shortages of laboratory supplies, such as pipettes and chemicals, often leading to delays in getting results.

Other scientists, like Dr. Zev Williams of Columbia University, are working on variants of rapid saliva tests that, like P.C.R., detect RNA, but don’t require expensive laboratory machines.

His team’s prototype takes just 45 minutes. It uses an array of portable equipment, including two tissue-box-size heaters.

That’s too bulky and expensive for at-home testing. But he said the test could be deployed in places where crowds gather, like schools, offices and travel hubs, granting safe passage to those who test negative while sending the infected back home.

His team has submitted an application for emergency approval from the F.D.A. In the meantime, they’ve partnered with Sorrento Therapeutics, a San Diego-based company, to scale up production.

The Columbia saliva test relies on a technique called LAMP that’s generally faster but a bit less accurate than P.C.R. The spit sample is briefly boiled and mixed into a cocktail of chemicals that then gets incubated at 145 degrees Fahrenheit for half an hour. If the tube’s contents turn from red to yellow, the test is positive.

The latest data shows the Columbia test performs as well as a laboratory deep-nose swab test more than 96 percent of the time, even when using saliva from sick patients who gave messy samples.

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“Even if there was food or blood, we took it,” Dr. Williams said. That wouldn’t fly with most other saliva tests in use, he said, which ban eating, tooth-brushing and even gum chewing in the hour or so before depositing drool.

Another saliva LAMP test is being tested by David O’Connor at the University of Wisconsin-Madison. Their technique bears many similarities to the Columbia test, including a color-based readout, but takes slightly longer and involves a couple of extra steps. Early trials of the test on volunteers in Wisconsin have gone well, Dr. O’Connor said, and one school district in Illinois is using the test to screen about 1,400 students and teachers on a weekly basis.

But saliva LAMP tests face their own hurdles. Saliva tends to clump and stick, and can be a difficult substance to handle and transfer from tube to tube, said Jennifer Dien Bard, director of the clinical microbiology and virology laboratory at Children’s Hospital Los Angeles, where her team is working to roll out saliva-based testing for coronavirus RNA. And although color-based results are simple, interpreting them can get messy if a rainbow of hues comes out the other end.

“To me,” Dr. Dien Bard said, “something like this might still belong in a lab.”

c.2020 The New York Times Company

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