Assuming this isn't addressed, here would be my house rule:
If the same disease is effecting everyone, check divided by 2 (round down) determines how many you can treat. To spread yourself thinner, divide the result by 1, and after the division(lack of division), subtract 5 from the result to determine the effectiveness of your healing.
If everyone has a different disease (hospital situation), and thus different treatments for each person, divide your check by 5, and to spread thinner divide by 2 then subtract by 5, the same way.