I suspect someone else can come up with a more formal equation but I would say look at the local estimate of R-0 and then perhaps consider the old 6 degrees of separation claim.
However, I think a slightly different, non-quantitative way is carefully associating and knowing something about how those you associate are acting in this context. As soon as you start feeling like your exposure may no longer be based on secondary or tertiary sources it would be time to self quarantine.
[Edit—I think it might be worth defining your population as well. Might not need to be the entire urban area/city/county but closer to neighborhood or apartment complex.)
I suspect someone else can come up with a more formal equation but I would say look at the local estimate of R-0 and then perhaps consider the old 6 degrees of separation claim.
However, I think a slightly different, non-quantitative way is carefully associating and knowing something about how those you associate are acting in this context. As soon as you start feeling like your exposure may no longer be based on secondary or tertiary sources it would be time to self quarantine.
[Edit—I think it might be worth defining your population as well. Might not need to be the entire urban area/city/county but closer to neighborhood or apartment complex.)