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.