GLASGOW, Scotland — In a gathering with more than 20,000 people from nearly every country, one of the biggest major international summits since the pandemic began, a coronavirus outbreak was always going to be a danger.

So far, organizers have not revealed the number of positive coronavirus test results. But on Saturday, the State Department confirmed that a member of the U.S. delegation had tested positive. Earlier, Mayor Eric Garcetti of Los Angeles tested positive days after arriving in Scotland.

The State Department statement Saturday declined to identify the person but said the official had been fully vaccinated and was quarantining. The statement also said John Kerry, the U.S. presidential envoy for climate change who is leading the negotiations at the summit, had received several negative coronavirus results, including daily lateral flow tests and a PCR test, since the delegate tested positive.

Asked about the number of positive tests at the conference, Alok Sharma, the British president of the talks, said the numbers were lower than in the rest of Scotland. “At this point, we’re comfortable where we are,” he said.

Still, delegates expressed concern.

“You are being exposed to more COVID than you would want,” said Marcelo Mena Carrasco, a scientist and former environment minister of Chile.

At the venue, the percentage of people wearing high-quality, certified masks indoors is low, he said. Air circulation in the meeting rooms was so poor that when he measured it with an air quality monitor, levels were much higher than is recommended for indoor settings.

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“This is supposed to be the COP based on science, and we’re supposed to be the ones who are basing decisions on science,” he said, “and this has shown that even the most basic things we’ve been hearing over the past two years haven’t really come through.”

The conference comes at a time when coronavirus cases in Britain are high. When asked about incidences of the coronavirus and the illness it causes, COVID-19, at COP26, a spokesperson for Police Scotland also said the force would not be making numbers public.

On Tuesday, a National Security Council aide who had traveled abroad with President Joe Biden’s delegation tested positive in Scotland and entered quarantine, a White House official said. The aide, who had not been in close contact with Biden, tested positive Tuesday with a rapid test but later tested negative through a PCR test, and was no longer in quarantine as of Saturday, the official added.

The United Nations has put in place rules to limit the virus’s spread. All attendees are required to take a coronavirus test, although the system is based on the honor code, since results are self-reported. Masks are required almost everywhere, and there are limits on the number of people allowed to gather in meeting rooms.

But inside the venue, social distancing is limited or nonexistent, and many attendees have their masks lowered. There are lines for food, bathrooms and crowds of people in the conference venue halls.

John Swinney, Scotland’s deputy first minister, said this week that a rise in cases in Scotland was “very unsettling” and warned of a possible increase as a result of the climate summit.