So, it's the city spirits that bring people here? [That's news to chaos; he's been told and has been telling others that no one knew what brought them here.]

If it was something in the air, I think we'd have seen effects in here from the breach by now - but the probe transmitted air samples, so we'll know soon enough regardless. If it does turn out to be something airborne, Nova City has environmental suit technology that should be protection enough if we can establish a clean zone - say, by adding airlocks to your safehouses.