Recently a stray cat came to my sister's property and had kittens. At about 11 weeks of age we brought one home to live in our house, this was about mid February. At the end of Feb (12 weeks old) we had him tested for FELV and FIP and test came up negative. Today my sister took two of the kittens for vet check ups (she had hard time catching them before now) They tested one and it came up positive for FELV. The told her to kill all kittens and mom but never tested the other kitten. I am very worried about my kitty. How often does it come up negative when it is really positive? or visa versa? What is the likelihood that they got the disease in the month and half that we have had Lightning. Please give me any info you can!!!!! I am very worried.