A woman working as a tour bus guide in Japan has tested positive for the new coronavirus for a second time, Osaka's prefectural government said.
It is the first known reinfection of Covid-19 in Japan, however, second positive tests have been reported in China, where the outbreak started in late December.
The woman, a resident of Osaka, in western Japan, tested positive on Wednesday after developing a sore throat and chest pains, according to a statement, describing her as being in her forties.
She first tested positive in late January and was discharged from hospital after recovering on February 1.
Health Minister Katsunobu Kato said in parliament the central government would need to review patient lists and keep tabs on the condition of those previously discharged, as health experts analysed the implications of testing positive for the virus after an initial recovery.
"Once you have the infection, it could remain dormant and with minimal symptoms, and then you can get an exacerbation if it finds its way into the lungs," said Philip Tierno Jr., Professor of Microbiology and Pathology at NYU School of Medicine.
Tierno said much remains unknown about the virus. "I'm not certain that this is not bi-phasic, like anthrax," he said, meaning the disease appears to go away before recurring.
Asked to comment on prospects for the Olympic Games going ahead in Tokyo this summer, Tierno said, "The Olympics should be postponed if this continues ... There are many people who don't understand how easy it is to spread this infection from one person to another."
Japan has changed its strategy in combating the contagion, seeking to slow its spread and minimise the number of deaths.
Around the world, health experts say more than 82,000 people have now been infected with the virus.
Of those, 32,878 have fully recovered while there have been 2,804 deaths. More than 46,000 people remain infected.
China remains the worst affected country overall, with almost 78,500 cases and 2,747 deaths.
However, new infections are soaring elsewhere, including in South Korea, which had 1,595 cases on Thursday, an increase of 334 in one day.
Cases are also growing in Japan, where there were 186 confirmed infections on Thursday, compared to 170 the day before.
Tokyo has said large gatherings and sports events should be scrapped or curtailed for two weeks to contain the virus, while pledging the 2020 Olympic Games will still go ahead in the city in the summer.
