A laboratory test using the so-called PCR method on Monday revealed that the president was positive for the virus, despite an antigen test having come out negative earlier in the day, his office first reported. The president then took two more PCR tests, one on Monday evening and another one on Tuesday, and both of them were negative.
False positive results in PCR tests, although rare, can occur.
As the head of state, the president is largely a figurehead in Portugal, where the prime minister and his Cabinet are in charge of day-to-day affairs. He wields large influence nevertheless, and he holds the authority to appoint the prime minister and dissolve parliament.
The Portuguese Cabinet is meeting Wednesday to decide on a new set of restrictions, and possibly a full lockdown, to combat the strong and steady resurgence of virus infections during the past few weeks.
Health authorities on Tuesday reported 155 new confirmed deaths for COVID-19, the highest single-day number since the beginning of the pandemic, bringing the total death toll in Portugal over the 8,000 mark.
There were also 7,259 new infections, bringing the southern European country of 10 million closer to 500,000 recorded cases.