I had a major infestation in my house when I bought it - it made my (100% house) cats very sick.
I got the cats injected with a drug (the name of which totally escapes me) tat stays resident for 6 months and renders fleas infertile if they feed.
I used permethrin based trigger spray on the carpets and bedding - at the time it was available freely in supermarkets, bt the law has canged in the past couple of years, and many products seem harder to get.
I found these links.
Safety Data
Some Products You Can Buy
University Of KY Guide to Flea Removal