The Delta Society, through their Pet Partners Program, trains and screens human and animal teams to safely visit with people in hospitals, nursing homes, school and other facilities. Delta Society's mission is to "help lead the world in advancing human health and well-being through positive interactions with animals. We help people throughout the world become healthier and happier by incorporating therapy, service and companion animals into their lives."
Debra White writes, in the November 2010 edition of Cat Fancy, that there are currently 10,000 dogs and 193 cats registered as therapy animals around the world. Over the course of Delta Society's Pet Partners Program they have had 1,000 cats registered total.
The number 193 struck me as rather small. I imagine there are a lot of people out there whose lives would be greatly enhanced from a visit with a therapy cat.