I think it's the person's hygiene/grooming, and not the cat's. I have a friend that does rescue, and she has between 6-10 cats in her home, at any time, and she and her house smell fine. She keeps all of the litter boxes in the basement and garage, and she, her husband and stepdaughter all scoop them out several times a day. If any of the cats have an accident, it gets cleaned up as soon as possible, so there won't be any lingering smells.