finding repeat admissions

I have a clinical database that has duplicate patient numbers in one column and dates (which will also contain duplicates) in the other. What I am trying to find are those patients that have visited the hospital more than once in any given day. The list is over 17000 lines so obviously I cannot do this manually.

So far I have used COUNTIF(X:X, X1)>1 to search column X for patient number duplicates. It narrows it down to 5000, which is still too big to search manually.

How can I ask Excel to search out patient numbers that have the same admission date compared to those that have different admission dates?

I have attached a truncated file with doctored numbers and highlighted 2 examples of what I mean.

Cheers