Most colds in cats are upper respiratory infections caused by a virus. These viruses are highly contagious. If one cat is sick with an upper respiratory infection, it is important to separate them from other cats to prevent spread of the disease. Here are my recommendations for isolating a cat at home.
1) Isolate the sick cat in a room or crate with a comfy bed, food, water and a litter box.
2) Cover your clothes with a protective gown and wear gloves while working with the sick cat.
3) Immediately dispose of feces, urine and left over food into a sealed garbage bag and trash can.
4) Disinfect anything the sick cat has come into contact with such as bowls, towels and litter before using it with healthy cats.
5) When the sick cat feels better, do not let them play footsie under the door as they can still transmit the virus. Keep the cat isolated for at least 2-3 weeks after their clinical signs resolve.
6) Make sure other cats in the household are current on their vaccinations. Since cats infected with feline herpes virus 1 are infected for life, vaccination is the only way to protect the other cats.
See Dr. Nelson discuss this in a video clip at http://www.ehow.com/video_12300350_separate-cats-colds.html.