This article is from the Feline Infectious Peritonitis FAQ, posted to rec.pets.cats newsgroup. Maintained by Erin Miller with numerous contributions by others.
It is suggested that queens be completely isolated from other cats (isolated in its own room, not its own cage within a room). This room should be empty for one week prior to placing the queen there, and should be disinfected with a 1:32 solution of bleach. The queen should be placed in the isolation room 10-14 days prior to delivery. All bowls and litter boxes should be used exclusively for that room, and not interchanged with any others. You should disinfect your hands when entering and leaving the isolation room. If possible, you should even try to have separate clothing, such as a smock and slippers which are restricted to the isolation room to decrease risk.
If the queen is not seronegative, you may want to consider an early weaning program. The queen should be removed from the kittens at age 4-6 weeks and never returned. During the first 4-6 weeks of a kitten's life, it gets its antibodies from their mother, therefore they are immune to anything she may be shedding. After that time period, they start making their own antibodies. If the queen is a carrier of coronaviruses, she can shed FECV to the kittens, and they are most likely to become infected during that time period. Regardless of whether the kittens are weaned early and isolated from the mother, they should be kept isolated from all other cats in the household. In addition to minimizing the risk of the kittens developing FIP, the risk of exposure to other viruses and diseases will be reduced.
Kittens should be raised in complete isolation from the queen and all other cats/kittens in the household until they leave the cattery. If the kitten is to be kept in the cattery, it should be isolated for 16 weeks, and then the FIP vaccination series should be completed before allowing the kittens to interact with the other cats.
Is there any evidence for this?
A 1992 study found the following: 400 kittens were divided into 41 household with various FIP histories. In one group the kittens were allowed to freely associate with all the cats. In a second group the kittens were isolated only with their mother. In the third group, the kittens were isolated by themselves starting at age 2-6 weeks. Only in this last group did all of the kittens remain seronegative for any/all coronaviruses.
That sounds absolutely ridiculous! Who would go through all that? Nobody says a breeder HAS to do any of this. These are merely the precautions currently recommended by the Cornell Feline Health Center and the recommendations which came out of the Winn Foundation sponsored Seminar on FIP/FECV. It is an option kitten buyers can use in determining which breeder to select if they so choose, but it is by no mean mandatory.