Centers for Disease Control and Prevention
Classification of Biological Agents
Clinical Microbiology Review 137
CATEGORY PRIORITY SPREAD IMPACT EXAMPLES
A
B
C
Bacillus anthracis, Yersinia pestis, Francisella
tularensis, Clostridium botulinum toxin,
smallpox, hemorrhagic fever viruses (Ebola,
Marburg, Lassa, Machupo)
Brucella, Salmonella, Shigella, E. coliO157:H7,
Burkholderia mallei, Burkholderia pseudomallei,
Chlamydia psittaci, Coxiella burnetii, Clostridium
perfringens toxin, ricin toxin, staphylococcal
enterotoxin B, Rickettsia prowazekii, viral
encephalitis viruses, Vibrio cholerae,
Cryptosporidium parvum
Nipah virus, hantavirus
Easily disseminated or
transmitted from person
to person
Moderately easy to
disseminate
Could be engineered for
mass dissemination
Highest
2nd highest
3rd highest
High mortality, potential for
major public health impact
Moderate illness, low
death rate
High morbidity/mortality,
major public health impact
