Well, my cats got fleas from the first and second stories of our house! As Nata wrote, they can come into your house via your shoes. I'd also add, clothing that may have been laid down in an office or store where an opportune flea decided to jump... or produce or a plant from a farmer's market or nursery. read more
Fleas In An Apartment Most bombs of the market (especially the ones you buy in the store and not from a vet) kill only living adult fleas, and not their eggs or young. You'll need to re-bomb or spray with a high quality product from the vet. read more