I know that the code first entry means there is another diagnosis code that must be prior to the diagnosis code with the code first entry.

I am wondering if the following note has the same meaning as code first:
"This category is provided to be used as an additional code to identify the viral agent in diseases classifiable elsewhere..."

This note came from the 079 heading. Can these codes, such as 079.4, be used alone or is that note stating that the ICD-9 guidelines require another code first?

Any input would be greatly appreciated.