My sister has only indoor kitties but she still has to dose them. I have 1 outdoor kitty and 1 indoor kitty and for whatever reason my outdoor kitty doesn't get fleas. I dose her just the same with Advantage as I was able to find it at our local Bomgaards store. I'll dose the indoor kitty this year too just to be safe. When I lived in Florida my daughter brought her animals with her when she came to live with me and they had fleas terribly. My 2 dogs who get dosed got their fleas as well as my house. My exterminator had to come every month and still I had those pesky fleas from her animals. After a year of trying I tried another brand of flea stuff for my dogs and after 1 month I had no more fleas. My little dog I couldn't put anything on him as he had a skin condition but by putting it on my larger dog that took care of it. Wish I could remember what I used as it was great stuff.
NOTE: I got rid of my daughter's animals as she didn't want to take care of them properly so found them good homes that would.