By Alex Leary and Daniela Hernandez
WASHINGTON -- President Trump tested negative for Covid-19 on consecutive days, White House physician Sean Conley said in a memo released Monday as Mr. Trump traveled to Florida for his first campaign rally since being treated for the virus.
Dr. Conley said tests and other measurements "have informed our medical team's assessment that the president is not infectious to others." The memo didn't specify when Mr. Trump was tested.
Mr. Trump was tested using Abbott Laboratories' BinaxNOW Covid-19 Ag Card, the memo said. The U.S. Food and Drug Administration has granted emergency-use authorization to Abbott Laboratories for a $5 rapid-response Covid-19 antigen test that is roughly the size of a credit card.
Infectious-disease experts have cautioned against relying too much on results from rapid tests, especially early during an infection, because of sometimes unreliable results.
"It is important to note that this test was not used in isolation for the determination of the president's current negative status," the doctor's memo said, adding that other data were used.
Dr. Conley said Mr. Trump's medical team relied on data including viral load, viral culture data and so-called polymerase chain reaction (PCR) cycle measurements to clear Mr. Trump for travel.
PCR tests work by amplifying parts of the virus's genetic material. The higher the viral load -- meaning the more virus there is in a sample -- the fewer cycles of amplification that need to be done to hit a certain threshold. Scientists use that cycle count as a proxy for viral load and infectivity, but it isn't a direct test, said Abraar Karan, a global health physician at Brigham and Women's Hospital and Harvard Medical School.
Dr. Karan and others said the gold standard to measure infectiousness is viral culture, which Dr. Conley cited without detail. It is a test that aims to see whether the virus in a patient sample can infect other cells. To do those tests requires specialized facilities that have heightened biosafety protections and are only available at certain research or government institutions.
"This comprehensive data, in concert with the CDC's guidelines for removal of transmission-based precautions," informed the team's assessment, the White House memo said.
The White House has faced pressure to disclose more information about Mr. Trump's testing, and it has declined to say when the president last tested negative before disclosing his positive result around 1 a.m. on Oct. 2, only days after his first debate with Democratic presidential nominee Joe Biden. Mr. Trump didn't disclose a previous positive test, while awaiting the findings from a more thorough coronavirus screening, The Wall Street Journal reported.
Concerns over Mr. Trump's condition led to a decision to cancel a second debate with Mr. Biden, the former vice president, on Thursday in Miami after the president declined to participate virtually.
Mr. Trump left the White House on Monday afternoon and boarded Air Force One without wearing a mask. He was due to speak in the evening to a crowd in Sanford, Fla., near Orlando.
It would mark his second public remarks since undergoing treatment for the virus. On Saturday, Mr. Trump spoke to hundreds of pro-police activists gathered on the White House lawn.
Dr. Conley on Saturday had also said that diagnostic tests showed there was "no longer evidence of actively replicating virus."
People infected with Covid-19 can stop isolating after 10 days have passed since the onset of symptoms, as long as they haven't had a fever in 24 hours and their other symptoms are improving, according to Centers for Disease Control and Prevention guidelines. For severe cases, the CDC says a person can be contagious for up to 20 days.
Mr. Trump was given a steroid, dexamethasone, typically recommended for severe cases of Covid-19. He has lauded the use of an experimental Covid-19 drug from Regeneron Pharmaceuticals Inc.
Mr. Trump also said in a tweet Sunday that he was now immune. Twitter Inc. attached a warning to the president's tweet, saying it violated the platform's rules on spreading misleading or harmful information about Covid-19.
Write to Alex Leary at email@example.com
(END) Dow Jones Newswires