Came across this with some organizers of protests in SC testing positive and requesting others who attended to get tested. Also an article mentioning about 1% (give or take) of people who decided to get tested and attended protests tested positive. Probably hard to say if that's how they got it if the percentage is that low and your'e not testing everyone.
From one of the articles:
Of the 3,200 people tested so far at the four popup sites across the metro, 1.8 percent have tested positive for Covid-19, says Ehresmann. HealthPartners, one of the largest health care providers in Minnesota, also reported to the state that it had tested about 8,500 people who indicated that attendance at a mass gathering was the reason they wanted a test. Among them, 0.99 percent tested positive. These numbers have been one of the few pleasant surprises since the outbreak began, says Ehresmann. “Right now, with the data available to us, it appears there was very little transmission at protest events,” she says. “We’re just absolutely relieved.”
In a handful of other US cities that have rolled out free testing for protest-goers, the first round of results look similarly encouraging. In Seattle, fewer than 1 percent of the 3,000 people tested after attending protests were positive for coronavirus, according to
a statement put out by the city’s mayor last Friday. This week, Boston officials
announced that 14 out of 1,288 people tested so far were positive for coronavirus, or 1.1 percent. Of course, these are only three cities out of hundreds that have been enveloped in large-scale protests against police brutality and institutionalized racism. Many are not conducting widespread public testing, and so signals of protest-related spikes may take longer to emerge. Additionally, the peak of protests in some cities, like New York City, San Francisco, and Washington, DC, arrived several days after actions in Minneapolis, where the response to Floyd’s death was swift and furious.
Still, these early numbers are welcome news to Roger Shapiro, a professor of immunology and infectious diseases at Harvard’s T.H. Chan School of Public Health. “When I hear a 1 percent positivity rate, that’s encouraging to me that these protests are not representing new hot spots,” he says. That’s because 1 percent is around the background level of community transmission that might be expected if one were to test a large sample of randomly selected people.
https://www.wired.com/story/what-minnesotas-protests-are-revealing-about-covid-19-spread/
https://www.thestate.com/news/local/article243694592.html