http://wefollow.com/twitter/hospital - does a great job of following and reporting on the top twitter users. These users are sorted by "tags" or "industries". wefollow.com does an excellent job of following the hospital industry and showing what hospital has the most followers.
This is an excellent tool for the twitter administrator at your hospital to compare yourself with other hospitals in the "twitterverse". You can see the "tweets" of others, as well as the numbers of followers.
As of this writing - wefollow.com is following 114 hospitals. With the top hospital being @myhospital - which is a specialty hospital in Amman, Jordan - they have 5,680 followers! At this point in time @myhospital has more than double the number of twitter followers as any other hospital on wefollow.com.
Rounding out the top 5 on their list is @childrenshealth with 2,907, @KHCC with 2,516, @khcf with 2,377 and @UMMC with 2,343.
This is a dynamic list that continually changes. Great information and an excellent source to see what other best practice twitter hospitals are doing.