Turn the tables here. Imagine you're a patient's partner or parent, and you find out that an employee of the hospital just may be infectious. Not guaranteed, but definitely came up positive at least once. How would you feel? Would you be inclined to hit the hospital with a lawsuit?
Or scenario two - for some reason there's a string of false NEGATIVES, and your friend is infectious and causes someone else to get ill. And he's working in your hospital. What would you do?
In cases like this, there can be no excuse for being anything less than 100% careful, and there will be an inquiry into how one or other set of results was false. Your friend will not be allowed back until the facts are found, and this may mean him enjoying some free paid leave.