The first US evacuee from China that tested positive for coronavirus was mistakenly released from a hospital in San Diego, according to health officials.
It marks the 13th case of the virus in the US, and the first positive case following the evacuation of a group of US citizens on a US State Department flight from Wuhan, China to a California air base.
The death toll from the flu-like respiratory illness has climbed to 1,000, with thousands of others falling ill in more than two dozen countries.
In San Diego, a woman was hospitalised with three other patients after showing potential symptoms following the flight from Wuhan, the outbreak's epicentre.
An initial test from the Centres for Disease Control and Prevention showed that all four patients did not have the virus. They were released on Sunday and placed into a two-week quarantine.
According to the CDC, further testing revealed that the woman did test positive for the virus.
"The confirmed positive patient was returned to UC San Diego Health for observation and isolation until cleared by the CDC for release", according to the University of California, San Diego Health.
Health officials are now investigating the patient "to determine contacts and to assess if those contacts had high risk exposures".
Another patient is also under medical investigation the hospital. Both patients are "doing well and have minimal symptoms", the hospital said in a statement.
Twelve other coronavirus cases in the cases have been confirmed in six states, including six other cases in California alone.
Medical experts have warned against Donald Trump's claims on Monday that the virus will "go away" in April because of the "heat", apparently conflating the flu season with the largely unpredictable viral behaviour of coronavirus.
His comments followed the recorded deaths of more than 100 people in China over the weekend and the ongoing quarantine of 3,700 passengers on cruise ship in Japan, where 135 people are confirmed to have the virus aboard the ship.
