I have had over 5000 cats through my doors and can truthfully say that includes some of the worst fleabags imaginable as well as wormy bellies.
I do not have a problem, I believe because I do treat all cats/kittens monthly in order to protect them from fleas.
Kittens are wormed at least monthly with panacur and when age and weight allow get Milbemax at least every 3 months,even monthly if any doubts exist.Adult cats get Milbemax at least every 3 months.
I think people forget the length of time flea larvae can hide in carpets,furnishings etc.
I think possibly those of us in rescue have very sadly seen death as a result of flea anemia or witnessed cats dying through serious cases of worms.
These treatments must be applied as directed, hit and miss yearly treatment is NOT enough. This is not aimed at anyone just pointing out something I feel very strongly about.
Just for the record I prefer stronghold because it treats earmites also.
It is also worth checking what the spot on treats as some treat ticks others dont,same with wormer some spot ons treat tapeworm only,others like stronghold only kill roundworm fleas etc.