If the Cards are testing positive today, then surely the Twins have to go into Quarantine and wait for results over the next 3-5 days. And that takes out the Indians too as they played last night.
The Brewers are theoretically ok as they shouldn't have come into contact with the Cardinals yet, hopefully.
That would mean two outbreaks (Marlins and Cardinals) have stopped games for the Phillies, Yankees, Blue Jays, Nationals, Brewers, Twins and Indians. Thats almost 1/3rd of the league.
If they are serious about trying to finish the year they need to embrace the idea of a fluid schedule. Shut teams down for a week to 10 days upon a positive case, and anyone they played in the last 3 days. Make up the schedule as you go with any teams who are left without opponents. Hopefully you can get every team to ~45 games.
I know I hate imbalanced schedules but I don't see any other way they can get the games in without seriously risking the health of everyone involved. The alternative is shut it down now and start putting in contingency plans for a series of bubbles in 2021 in case there is no vaccine available. I wonder how difficult it would be to build a facility on an island somewhere similar to the UFC Fight island idea. You don't need stands, just a fence and facilities for TV cameras/lights.