These are just a few tips to help you in your search:
Leave out minor words such as with, during, the, etc.
If the disease you are looking for is a phrase, it's best to search it with quotes around it, such as "deep vein thrombosis." This tells the database to search for those words together in that specific order.
In most databases, if you type the beginning of a word and then type an asterisk (*), the database will match any word that begins with those letters. For instance: nurs* matches nurse, nursing, nurses...