The Centers for Disease Control and Prevention's (CDC) Category A, B, & C Agents by Definition.
Category A Diseases/Agents
The U.S. public health system and primary healthcare providers must be prepared to address various biological agents, including pathogens that are rarely seen in the United States. High-priority agents include organisms that pose a risk to national security because they:
Can be easily disseminated or transmitted from person to person
Require special action for public health preparedness
Result in high mortality rates and have the potential for major public health impact
Might cause public panic and social disruption
Category B Diseases/Agents
Second highest priority agents include those that:
Are moderately easy to disseminate
Require specific enhancements of CDC's diagnostic capacity and enhanced disease surveillance.
Result in moderate morbidity rates and low mortality rates
Category C Diseases/Agents
Third highest priority agents include emerging pathogens that could be engineered for mass dissemination in the future because of:
Ease of production and dissemination
Potential for high morbidity and mortality rates and major health impact