If the event is that you've found sick tribespeople, they may or may not be diseased.  If that chance comes up (I don't know the odds), they'll disappear again after a few turns.  I think there's an event notification, but I don't recall; it's been a few weeks since I've had that on pop up.

Thank for your interest. I am sorry I did not pay attention if the spawned unit was sick or not. However, I do not think so, because it has disappeared just the next turn, twice, at each time. And I am sure there was no game information for this disappearance, twice, at each time.