counting the number of multiple unique patients entries

This is my first post here; hopefully I will be able to make this as clear as possible. I have quite a large database (approximately 10.000 entries) containing the records of patients’ bacterial isolates (one bacteria). Patients are continually screened for the presence of this bacterium, so each patient has multiple entries. When processing the data only the first entry for each patient is significant. I need to find out how many times each patient appears or how many 'sessions' a person does throughout the entire database and then select only first isolates.
I have a table that has records of each person (i.e. name), and the dates. There are several thousand persons in the database, and a patient will often appear in the database many times.
I am using Excel 2007, and while I am not a total novice in Excel, I most definitely need help here.

Thank you very much for your time.

thanks for the tip about advanced filtering. i have never tried that and it does help. however, that is only suitable for a quick analysis, i would require count of all isolates per patient (numbered isolates)i.e.
patient 1, isolate No. 1
patient 1, isolate No. 2
patient 1, isolate No. 3 ect.
there is a problem that i haven't explained earlier - i still need to check subsequent isolates (advanced filtering just removes them) as the bacterial resistance changes over time, and an isolate No.3 with different antimicrobial susceptibility is counted as a new isolate. any ideas?