13 positive COVID-19 tests in one Major League Baseball clubhouse During the first week of the MLB season, the coronavirus spread through the Miami Marlins. Players have been quarantined, and their next two games postponed.

Three days into their season and the Miami Marlins have at least 11 players testing positive for the coronavirus. (Mitchell Leff/Getty Images)

Why can’t the Marlins keep playing?

Twelve Marlins players and two coaches have reportedly tested positive. How likely is it that other Marlins have contracted the virus, and haven’t yet tested positive, but will in the coming days?

“Very likely, unfortunately,” says Kathleen Bachynski, an epidemiologist at Muhlenberg College.

“Quite likely,” says Ron Waldman, an epidemiologist at George Washington University.

“Yeah,” says Jared Baeten, an epidemiologist at the University of Washington. “If it was one player, totally different. But clearly, to get to 13, there are not 13 separate introductions [of the virus] into the Marlins organization. There is transmission within the team. And if there is transmission in the team, there's great chance that there is still unrecognized transmission within the team.”

In other words, the three Marlins players who received positive test results Sunday morning spent Saturday with teammates while infectious. The seven players and two coaches whose tests came back positive Monday morning spent Sunday with teammates while infectious. If those teammates contracted the virus this past weekend, however, we won’t know whether they have or haven’t for at least another few days. We probably can’t be sure any of them isn’t infected until sometime next week. Because the virus takes time to incubate.

“You cannot assume that you have identified everybody who is infected,” Binney says.

Would super-frequent testing allow the Marlins to safely continue playing?

No, because even MLB’s expedited testing process comes with a lag time between test and result. “Even if you're doing regular testing,” Binney says, “you have this space, in between when somebody gets infectious and when you get a positive result back, where they can be spreading the virus.” The more frequent the testing, and the quicker the turnaround time, the smaller that space is. But it's impossible to eliminate it entirely.

So, if the Marlins continue to play, and continue to spend time in clubhouses together, and continue to have close contact with one another, they increase the probability that the virus will spread further – including to “taxi squad” players they’ve called up to replace those who’ve tested positive. Then the outbreak grows, and the Marlins struggle to field a team. Manfred said Monday that “a team losing a number of players that rendered it completely non-competitive” was the threshold for shutting that team down.

“You're going to be getting cases coming up over the next few days,” Binney says. “And if you keep playing, then the disease is not going to stop.”