Question: Can ICD-10 codes for bacterial and viral infectious agents ever be used as primary diagnoses? AAPC Forum Participant. Answer: The instruction that accompanies the B95-B97 (Bacterial and viral infectious agents) codes tell you that “these categories are provided for use as supplementary or additional codes to identify the infectious agent(s) in diseases classified elsewhere.” So, you would never use a code from this range as a primary diagnosis. If a provider documents the infection only, and does not document a specific disease, then you should use a different code such as A49.8 (Other bacterial infections of unspecified site) or A49.9 (Bacterial infection, unspecified).