Tech entrepreneur Elon Musk says he "most likely" has a "moderate case" of Covid-19 but has been "getting wildly different results from different labs".
The boss of Tesla and SpaceX, who is 49, tweeted his symptoms were those of a "minor cold". On Friday he said he had been tested four times, with two positive and two negative results.
Mr Musk appeared to play down concerns about the pandemic when it first hit.
Covid-19 has now infected nearly 10.9 million people in the US.
More than 245,000 people have died there, and more than 67,000 people are currently in hospital.
Some 35 US states now require face coverings to be worn in public and many are urging residents to stick to social distancing amid fears their health care systems will be swamped with infected patients.
Am getting wildly different results from different labs, but most likely I have a moderate case of covid. My symptoms are that of a minor cold, which is no surprise, since a coronavirus is a type of cold.— Elon Musk (@elonmusk) November 14, 2020
Mr Musk, who has 40 million followers on Twitter, said about his symptoms that he was "a little up & down. Feels just like a regular cold, but more body achy & cloudy head than coughing/sneezing".
On Friday, he had questioned the veracity of rapid antigen testing, tweeting: "Something extremely bogus is going on. Was tested for covid four times today. Two tests came back negative, two came back positive. Same machine, same test, same nurse."
He said he was awaiting the results of PCR (polymerase chain reaction) tests, which are regarded as the gold standard by epidemiologists and the one used most around the world.
Back in March, Mr Musk had tweeted to his 32 million followers on Twitter: "My guess is that the panic will cause more harm than the virus."
Two months later he threatened to move his electric car firm's headquarters out of California after his Tesla factory was ordered to stay shut because of lockdown measures.
Mr Musk's SpaceX firm is set to launch four astronauts to the International Space Station on Sunday. Nasa chief Jim Bridenstine on Friday ruled out the presence of anyone who tested positive for Covid-19 at the Kennedy Space Center.