countif column range equals any other cell in same range

Hi all,

I'm trying to count the number of re-admissions within a certain time frame (let's say no more than 60 days apart) by sorting data by patient id# then discharge date and counting the number of repeat values in this column that occur within this time frame. I was thinking a COUNTIFS would do the trick but do not know how to tackle the issue of writing a criteria expression for any cell in a cell range equaling any other cell in that same range. Basically I need the number of occasions where an ID# is reoccurs inside the time window.. So an ID# that shows up 9 times but only 4 instances of closely spaced consecutive service would count as 4. Also, a count of unique patient ID#s that fulfill the re-admission criteria would be useful..

I suppose this is a common manipulation in business terms as "repeat customers"..
Any help would be much appreciated. Thanks!