AFB and sputum culture question

[Birdy2]

So with TB I've noticed that Drs will do an AFB smear and culture, along with many other things. If the smears are negative X3 they take patients out of isolation. My question is what about the culture that takes two weeks? I looked it up and often times the culture will come back positive when the smear is negative. Isn't it kind of stupid to take them off isolation and risk everyone getting TB? Do doctors know this about cultures? Surely they do. And what else are they going by when they make the decision to take them out of isolation? The particular patient I'm talking about had CT, bronch, and something else I can't remember. The ct showed tons of fluid, bronc showed large amounts of necrotic tissue. This person had all the symptoms of TB and stated his father actually passed away from it.