Blazej Spychalski wrote on Twitter that the conservative leader was tested the day before and his result was positive. He said the president felt well and is in isolation.
Duda's diagnosis comes amid a huge surge in the number of confirmed cases of Covid-19 and deaths in Poland, a nation that saw only very low numbers in the spring.
The spiking infection rates are pushing the country's strained health system to the breaking point. Doctors say patients are now dying not only from Covid-19, but from other illnesses that overwhelmed hospitals are not able to treat.
The government is preparing to open field hospitals but it is not sure where it will find the doctors and nurses to staff them.
Duda, 48, visited the National Stadium in Warsaw, which is being transformed into one of the field hospitals, on Friday. He also met with Iga Swiatek, the 19-year-old Polish tennis player who won the French Open earlier this month.
The Polish government imposed new restrictions on Saturday that are just short of a lockdown, in hopes of bringing the country's outbreak under control.
Hundreds gathered on the streets of the capital at the end of the week, to protest legal restrictions on abortions after a court ruling, in the largely Catholic country.
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Prime Minister Mateusz Morawiecki appealed Friday to Poles to strictly observe these “serious restrictions” in order to protect lives. The appeal came as the nation of 38 million hit another daily record of new infections, over 13,600, with 153 new deaths.
Overall, Poland has recorded 4,172 virus-related deaths in the pandemic.
Duda's key constitutional roles include guiding foreign policy and signing legislation. But most of the day-to-day governance is the responsibility of Prime Minister Morawiecki and his cabinet.
In nearby Slovenia, Foreign Minister Anze Logar also tested positive for the coronavirus. The Foreign Ministry said Logar was self-isolating for the next 10 days.
The official STA news agency said Logar was on a tour of the Baltics earlier this week and attended a session of European Union foreign ministers in Luxembourg earlier this month.