I have 3 indoor cats and still get flea infestations. It's ME bringing them in from outside! So I have to have Animal Reg come in and trap the racoons, possums and skunks that cruise through my yard every night, dropping their fleas as they come to fish in my pond!
Any flea within 100 yards will beat feet to get to me!
And vacuuming every day does help, but unfortunately I don't have time for that