A cat doesn't test positive for FLV if he's had the shots.

FLV is contagious though saliva, but the virus only survives for a few hours exposed to air. Standard soap and water cleaning (a little bleach couldn't hurt) should make dishes and boxes safe for other cats.

I have four kittens (now 8 months old and huge!) who tested positive at 8 weeks and 6 months, but are asymptomatic. Tbey are isolated from the other cats.