HIV (Human Immunodeficiency Virus) leads to AIDS if left untreated. With modern therapy (cART), HIV is now a chronic, easily controllable infection: with complete viral suppression, the person is no longer contagious ("U=U" - Undetectable = Untransmittable).
Prevention: condoms, PrEP (preventive tablet), PEP (emergency medication within 48-72 hours of possible contact). Swiss contact points: AIDS Help Switzerland, checkpoints, HIV consultation hours at university hospitals.