Health and epidemics
Disease spreads through a settlement like fire through dry grass — and you will not see it until someone falls.
Outbreaks
Pathogens emerge from the conditions a colony lives in, and they spread person to person while nobody is looking. What you observe is symptoms, not the infection itself — by the time the first colonist is visibly sick, the honest question is how many others already are.
Detection, containment and treatment are separate problems. A Clinic and a capable Medic carry the medical response — and they carry it together: the building treats nobody until a qualified medic actually holds its position and staff are assigned to work it. There is no switch to flip in an emergency, which is the point. Quarantine decisions are yours, and they cost you exactly the people you quarantine.
Prevention
Prevention is a research posture, not a reaction: work like Immunization lowers the odds of emergence and blunts what does break out. It is the classic invest-or-risk dilemma — the turns spent on it are turns something else did not get, and its payoff is the epidemic that never happens.