What's the name of this star trek episode?

ok so, i know, first of all, it's not star trek from the 1960s or the new one form the 2000s...its where either enterprise or voyager try to save these humanoids on a planet who are suffering from a medical condition, while the other group of people, who are primitive, are the ones who will survive, now i THINK beverly crusher is in the episode i just can't remember which episode it was, anyone know?