A surveillance program designed to help determine the prevalence of novel coronavirus infections across King County has been put on hold because of concerns by the U.S. Food and Drug Administration (FDA), leaving some participants in the dark about their test results.

The SCAN program, launched March 23, relies on home-testing kits that allow volunteers to swab their own noses and send the specimens to a central lab for analysis.

The technique was allowed by the Washington state Department of Health under an emergency-use authorization(EUA), but now the FDA says a federal EUA is also required before the program can notify participants of their test results, according to a statement posted Wednesday on the SCAN website.

The statement says the study team has been sharing information about the safety and reliability of the self-swab system with the FDA over the past two months as part of their application for federal authorization and in response to questions from the agency. On May 11, they received a notice from the FDA directing them to “discontinue patient testing and return of diagnostic results to patients until proper authorization is obtained.”

“The concern is in regards to at-home collection,” an FDA spokesperson said Thursday. The agency needs to determine whether people can safely and properly collect their own specimens, whether the media used to transport the specimens are safe and whether the specimens remain stable during shipment, no matter the temperature, the spokesperson added.

Seattle resident Rochelle Kochin, who sent in her swab on Monday, was frustrated to discover the project is suspended.

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“They told us: ‘We will call you if you’re positive,’ ” Kochin said Thursday. She’s worried some people who might have tested positive will assume they are negative because no one is now making those calls. “I find it outrageous that I will not be given the result of a test that I took as I was promised because of the FDA,” she said.

Kochin said she doesn’t have symptoms, but she and her husband recently returned home from  Pennsylvania. “I don’t have any known exposure, but we were on an airplane.”

A spokesperson for SCAN said the project hopes to resume testing and notification of results soon. The project was never intended to substitute for medical services, and any participants who suspect they may be infected should stay at home and consult their health-care provider, the spokesperson added.

The self-swab approach was pioneered by a project called the Seattle Flu Study, which had been using it for nearly two years to track the spread of flu and other respiratory diseases.

The SCAN program has tested more than 8,500 specimens from volunteers so far, with a 1.3% positive rate among people with symptoms. At least five people with no symptoms also tested positive. The results confirmed that many infections are not being diagnosed and that the number of known cases represents the tip of a much bigger iceberg.

In combination with the Seattle Flu Study, more than 17,000 self-swabs have been collected and analyzed with only one “minor adverse event” — a person who reported discomfort after using the swab. The SCAN statement also says the team has shown that the technique is reliable and that specimens don’t degrade during shipping.

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The FDA has also questioned the project’s testing of people with no symptoms, but the statement says that’s important in order to understand the role of asymptomatic people in spreading the disease.

Companies are rushing to develop home-testing for coronavirus, but the FDA in late March blocked sales of commercial kits, arguing that they might be unreliable. The agency has since offered new guidelines for home-testing that say: “Any COVID-19 test intended for at-home testing, including self-collection of a specimen at home … requires an authorized EUA.”

The Seattle Flu Study also ran into regulatory problems early in the epidemic. Researchers developed their own test for the new virus and detected some of the state’s first infections and evidence of community transmission in samples from volunteers. But the project was temporarily suspended because, while approved for research testing, it lacked FDA approval for clinical testing.

Both SCAN and the Seattle Flu Study are funded by Gates Ventures, Microsoft co-founder Bill Gates’ private office. The Bill & Melinda Gates Foundation has also been funding research to determine the reliability and usefulness of self-swabbing systems for widespread coronavirus testing.

It’s not clear when the SCAN program will resume testing.

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