So far two M.L.S. clubs have been forced to withdraw from its tournament after multiple players tested positive after arriving at the site. FC Dallas had 10 players and one coach test positive before competition began. On Thursday, the second day of the tournament, Nashville SC was forced to pull out of the event after nine players on its team tested positive.
Binney said the coronavirus’s incubation period, which normally lasts around three to five days but can be up to two weeks, probably made it tough to catch cases over a short period of testing. It would be another few days before the league could be sure that the virus had not spread to others there.
That is why Briana Furch, an infectious disease specialist who has informally advised a number of N.B.A. players this summer, has urged athletes to continue to exercise caution even upon arrival in a bubblelike environment. She said they should wear masks, practice social distancing and wipe down surfaces, whenever possible.
“In a bubble it can still spread like wildfire,” she said.
Have semi-enclosed environments worked elsewhere?
The early success of the National Women’s Soccer League’s restricted campus might provide a sense of hope for other sports. The teams there have shown no positive cases since play began on June 27.
They have had a few factors working in their advantage. They did have an outbreak within a team, but were lucky that this cluster of infections — 10 positive cases among the players and staff of the Orlando Pride, which ruled the team out of the competition on June 22 — happened before the individuals arrived at the site in Utah. They have fewer people there, meaning there are fewer opportunities for infection. And the virus around the world, in general, seems to be hitting men harder than women.
But on a basic level, Binney said, “The N.W.S.L. bubble is a proof of concept that a bubble can work.”
What about the virus outbreaks outside sports’ sites?
Infections, particularly in the South and West, have been surging for the past month. And experts reiterated that no matter how tightly controlled a sports league’s restricted space might be, it will still exist within, and be affected by, a larger surrounding ecosystem.