We studied over 40 possible risk factors for feline upper respiratory infection (URI) at 9 shelters across North America over the course of a year. The results were dramatic: independent of the intake numbers, the risk for URI varied more than 50 fold. The most important factor?  It was simply space: more than 9 square feet of floor space, and a two compartment cage that permitted daily care without moving the cat to a new cage during the critical first week of care.