But Tore Steen, the doctor in charge of infection control in Oslo, said that there was no sign that the demo had been a superspeader event.
“It's been a lot of days now, and so far it looks like there was very little infection during the demonstration in Oslo, but we can't say that for sure yet,” he told Norway's state broadcaster NRK.
“If a lot of people had been infected it could have been serious, but nothing indicates that it has led to any major outbreak.”
He said it was likely that the person had been infected during the protest.
“We are aware of a case where a person who participated in the demonstration in Oslo tested positive for the virus at the end of last week,” he said.
“As the person took part in the demonstration, the probability is that that is where the infection originated, but that's only an assumption. The person may have been infected somewhere completely different, it's not easy to say.”
The Oslo authorities are not, however, asking all those who took part in the protest to get tested, as health authorities in Denmark did when someone tested positive for coronavirus after a similar protest in Copenhagen.
“It would be a bit much if everyone went and got tested because of one possible infection,” he said. “But if it turns out that more participants have been infected, we'll look again at the situation.”
Police decided not to intervene to enforce social distancing rules at the Oslo Black Lives Matter protest on June 5th, meaning many of the protestors were crowded closely together.