Keep your house clean and use Advantage or Revolution once a month on
your cats. Don't use insecticide foggers because they are toxic to
cats.

Also, stop using the Ultraguard Plus immediatly. Like I said, keep the
house clean and give the cats Revolution once a month.

http://www.hartzvictims.org/modules.php?name=News&file=article&sid=1446

Buy revolution. Your vet will stock it, but you can usually get it cheaper
at an online vet supplies store. Google 'pet supplies' and see what comes
up. Revolution is a treatment you put on the back of their neck once a
month. It kills fleas, ear mites, worms (except tapeworm) heartworm and
ticks. Each treatment lasts one month, can be used on kittens over 6 weeks
of age and you get 3 treatments per pack, about $30-$40 per pack. There are
other similar products like advantage, they all do pretty much the same.
Treat your cat first, then flea bomb your carpets. Keeping them inside will
stop them bringing more in. Fleas they catch outside will die on them as
long as they are protected by revolution, but will still jump off into your
carpet, so keep them in if possible so this doesn't happen.