Giardia….

Those of you who have had animals that have had Giardia…. How often did they get reinfected? Can it completely go away or does it stay with them for good? My two cats got it for the second time within a two month span. I adopted them in mid June & one of them (unbeknownst to me & the shelter) had it & gave it to the other cat I adopted with her….
I have cleaned my apartment top to bottom the first time, washed everything I had on high, steam cleaned my carpets, etc. How did you guys get rid of it & keep it away????