Our two cats had massive flea infestation. The flea infestation have both been around for about 5 weeks in spite of applying Frontline Spot On. According to the description fleas should die like ticks after 2 days, I can not really say whether both bring always new fleas or whether they survived despite Frontline. Our apartment has been cleaned several times thoroughly steam cleaned and misted with anti insect repellent from the pharmacy. Nevertheless, the flea infestation is still going on.