Los Angeles County will stop using Curative COVID-19 tests at pop-up testing sites after a U.S. Food and Drug Administration advisory to patients and health care providers that the test could produce false negatives.

The county Department of Health Services said in a statement Sunday that the change to Fulgent Genetics tests will take place this week.

“We trust the FDA and I think it’s our obligation to follow their guidance wherever possible,” department director Dr. Christina Ghaly said during a media briefing on Monday.

She said health officials believe the Fulgent test is accurate, but warned all tests have a risk of false negatives. Faulty results pose a big risk from a health perspective because people who are erroneously told they don’t have the virus can unknowingly spread it.

“Even if you test negative, it is critically important to self-isolate for 14 days after exposure or 10 days after symptoms start. You may still have COVID-19 and spread it to others,” the county statement said.

Curative PCR tests used at the pop-up sites between Dec. 13 and Jan. 2 made up just 10% of all COVID-19 tests administered at county-supported test sites during that same time frame, the statement said.

The testing switch comes as California, and particularly Los Angeles County, copes with its worst surge of the pandemic and some of the highest levels of COVID-19 in the country.

Mayor Eric Garcetti, who embraced Curative and opened testing to everyone last spring when supply was short elsewhere, stood by the company last Thursday after the FDA advisory came out. He said a third of the city’s positive test results have been in asymptomatic people.

“That’s 92,000 people who otherwise might not have known, might have been spreading,” he said during a briefing last week. “That has helped us predict those surges in hospitalizations and deaths as a result. To me that proof is in the pudding.”

Curative has said it is working with the FDA to respond to concerns and would provide additional data to address test limitations and precautions highlighted by the agency. The California startup said its test was the most clinically sensitive available at scale and its performance had not changed.

Associated Press