A viable microorganism (or its toxin) which causes or may cause disease in humans or animals. Includes those agents listed in the Department of Health and Human Services' Regulations (42 CFR 72.3) and any other agent that has the potential to cause severe, disabling, or fatal disease.

Note: The ETIOLOGIC AGENT label specified in the regulations of the Department of Health and Human Services may be applied to packages of infectious substances.