It gets into the homes by sick people visiting the home, who picked it up from visiting another sick person.cone said:
if homes are the major vector, it has to get into the homes somehow
In my sister's case, her friend caught it in the hospital. She then proceeded to infect everyone who visited her after her surgery. Then the people that visited her went home and spread it to their households (my sister's entire family caught it from her). So the original infection occurred in the hospital, but it spread to a bunch of households through in-home visits.
When you crunch the numbers - the vast majority of people in my sister's case got it from household spread, even if the original infection occurred in the hospital. I think this is where you get something like 80%+ transmission from household spread.