My experience: Roundworms are not always noticed in the stool sample exam! If a cat is indoor/outdoor, it is best to give them a Drontal pill every three months, just in case, which destroys both roundworm and tapeworm. Integrate it along with your flea/tick prevention schedule.

Debra was trapped and vetted; stool negative. Kept strictly indoors, a few weeks later she was vomiting what resembled angel hair pasta (roundworms!) and when I questioned the vet about it I was told that the roundworms do not always show in the fecal matter. I never noticed anything unusual in her litter box. And here I thought I was bringing home a spayed, healthy, parasite-free cat from the vet! At least Lily could not catch it unless she ate the infected stool, which was a relief.