Fleas live outside in the dirt. The cats have fleas because of the yard LOL.
But anyway, spraying is all you can do. It's a pain. I do use diatomaceous earth and it helps a lot. I used it for ants, not for fleas. It must have helped the fleas too because this has been a good year all the way around flea wise. It's a white powder that is like fine glass shards to the fleas.
Diatomaceous earth is not poisonous to us. You can powder the floors and or carpets and it will help some.
Do you have pets? You'll need to use frontline on them if you do. Fleas have to have a blood source and usually humans only is not enough.
We've never had them bad enough to have to treat the inside of the house or to spray the yard. So long as we treat our dogs we do fine. Our cats never leave the house. They only get it if we don't treat the dogs fast enough. This year I've been super careful to treat the dogs and keep them flea free. So our cats have been perfect.