TOKYO — An outbreak of infections among members of the South Africa men’s soccer team emerged as the first test of Olympic officials’ strategy of aggressive testing and swift isolation to prevent the spread of the coronavirus during the Tokyo Games.

Two dozen people affiliated with the South Africa soccer team, the vast majority of them athletes, are under individual quarantine after three team members tested positive, Olympic officials announced Monday. They were the first athletes to test positive from inside the Olympic Village, where thousands of players and staff reside and dine.

Later Monday, the U.S. Olympic and Paralympic Committee announced that an alternate for its women’s gymnastics team had tested positive, and another was considered a close contact. USA Basketball also announced Monday that Katie Lou Samuelson would be unable to compete in women’s three-on-three basketball after being placed under health and safety protocols Saturday. She’ll be replaced by Jackie Young.

Coming four days before the Opening Ceremonies, the incidents underscored growing fears about whether the Games would end up a superspreader event. The rise of the delta variant around the world and coronavirus infections in Tokyo have raised concerns about the thousands of foreign visitors entering Japan.

Yet Olympic organizers have remained steadfast that their testing-and-quarantining regimen is effective. Officials say their approach is designed to ensure a “covid-safe,” not necessarily a “covid-free,” Games.

“There will be, of course, a certain number of positive cases to be found in the lead-up to the Games. But once again, the most important thing is the response to the positive cases,” Tokyo 2020 Organizing Committee spokesman Masa Takaya said during a news conference Monday.

Vaccines are not required of anyone entering Japan, but visitors and returning residents are required to have two negative test results within 96 hours of departure and another negative result upon landing.

Every member of the soccer team followed those protocols, the team’s chief medical officer, Phatho Zondi, said in a news release. The three team members tested positive during regular daily screening from inside the Olympic Village two to three days after their arrival in Tokyo.

“The timing of the positive results suggests that the PCR test in these individuals was done during the incubation period of the infection, which is how they could be negative in South Africa and then positive in Japan,” Zondi said. “They are now in isolation where they will continue to be monitored and will not be allowed to train or have any physical contact with the rest of the squad.”

A fourth member of the South African delegation, a rugby coach, tested positive Sunday.

Information about where the infected and exposed team members traveled within the Olympic Village was not immediately available Monday.

Six athletes and two staff members of the British delegation are self-quarantining after being exposed as close contacts of someone who tested positive upon arrival and was not a member of the delegation, the BBC reported.

Athletes are screened daily, and those who test positive or are exposed must isolate or quarantine in individual rooms, get meals delivered, ride transportation individually and refrain from training or playing until they are cleared by medical staff.

The South African team is unable to practice ahead of its scheduled match Thursday against Japan. Takaya said Tokyo 2020 officials will discuss whether the match will take place.

Public support for the Olympics remains lukewarm, and some of the anxiety has seeped into some sponsorships. Toyota, a top sponsor of the Games, announced Monday it will not air any Olympics-related television advertisements in Japan and that its officials will no longer attend any of the events, including the Opening Ceremonies, according to media reports.

Japan has barred all spectators from Olympic events in and around Tokyo in an effort to curb the spread of the virus. Olympic officials noted that the opportunity for residents of the Olympic Village and the general Japanese public to interact is “incredibly limited” and that the Games would not pose a risk to residents unaffiliated with the Olympics.

More than 22,000 athletes, Games personnel and journalists have entered Japan since July 1. So far, 61 people have tested positive for the coronavirus, and 28 of them were overseas arrivals — or about one-tenth of 1 percent, Takaya noted.