Summarize this article:

It is important to know how FIV is spread so that you can keep your FIV-free cats healthy and make sure that your FIV-positive cat still has a happy life. FIV is most commonly spread through a cat's saliva, though it can also be spread through blood and semen. The most common way for a cat to contract FIV is through getting bit by an FIV-positive cat. Keep in mind that FIV is a relatively fragile virus that cannot survive in the environment beyond a few seconds. Outside the body, FIV is rapidly damaged by drying, UV, heat, light and basic disinfectants, and poses no risk to other cats. The virus requires direct transmission from infected saliva of one cat, into the bloodstream of a healthy cat. Studies have shown that it is not absolutely necessary to keep your healthy cats separate from your FIV-positive cats if they get along well. If your cats have a tendency to fight, however, it is a good idea to keep them separate. In studies done by the University of Glasgow, it was found that when FIV-free and FIV-positive cats were around each other, there was a 1-2% transmission rate. You will have to decide whether that 1 to 2% is too much of a risk to take. When cats get spayed (females) or neutered (males), they become less aggressive, which means that the chances that they will get into fights is greatly reduced. If you have an FIV-positive cat that you want to remain an outdoor cat, it is a good idea to get it fixed so that it is less likely to bite another cat in a fight. As a responsible cat owner, your priorities should be to keep your FIV-positive cat healthy, and to make sure that it does not infect any other cats. Male cats tend to roam over large distances, sometimes across several acres and are likely to encounter other cats on their travels. If he is likely to scrap with these cats, then it is essential to keep him indoors. Keeping a territorial cat indoors might not be the most ideal situation, particularly if he is used to roaming around outside, but it might be the only way to keep him from spreading FIV to other cats in your neighborhood. If you live in a city, it is a good idea to talk to a local veterinarian about the incidence of FIV in the area. If there is a large population of feral cats who are FIV-positive, you may want to keep FIV-free cats indoors but may feel alright about letting your FIV-positive cat stay an outdoor cat. If FIV is rare in a high cat density neighborhood, then, as a responsible owner, you should keep your FIV-positive pet indoors. If you live in an area with a low population of cats, such as remote countryside, then the risk of cats meeting and fighting is low, and it is acceptable to let your FIV-positive cat out.
Understand how FIV is transmitted. Consider keeping your FIV-positive and FIV-negative cats separate. Spay or neuter your FIV-positive cat. Keep a male cat indoors if he is likely to get into fights with other cats. Talk to a vet about the health of cats in your area, particularly if you live in a city.