Plague, Pneumonic
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Diagnosis Synopsis
Pneumonic plague is a severe bacterial lung infection caused by the gram-negative bacillus Yersinia pestis, which is found in rodents (eg, prairie dogs, squirrels, rats, etc) and their fleas, and sometimes in cats. Y. pestis can also cause bubonic and septicemic plague (bubonic plague associated with sepsis and delirium), either of which may progress to the pneumonic form. The bubonic and septicemic presentations are discussed separately.

Pneumonic plague is classified as a Category A bioterrorism agent because of its ease of dissemination, contagiousness, and high mortality rate. The most likely method of dispersal would be as an aerosol, but simply having an infected individual walk around infecting others is also a likely mode of dissemination. It has an incubation period of 1-6 days (average 2-4 days) and can be transmitted person to person via droplets through direct, close contact.

Pneumonic plague results in a severe fulminant illness that develops with associated high fever, chills, headache, productive cough, chest pain, hemoptysis, extreme malaise, myalgias, tachypnea, tachycardia, and pneumonia. GI symptoms, including nausea, vomiting, abdominal pain, and diarrhea are also commonly seen. If not treated within 24 hours of onset, pneumonic plague rapidly progresses to acral cyanosis, respiratory failure, septicemia, circulatory collapse, and death. Untreated, the mortality rate is 50-90%. With treatment, the rate is 15%.

Endemic plague is seen in the southwestern United States (Colorado, New Mexico, Arizona, California). Plague is also seen in Vietnam, India, the former Soviet Union, and parts of Africa. Naturally occurring pneumonic plague is uncommon. Hikers, campers, veterinarians, and owners of infected cats, especially those living or visiting endemic areas, are at risk for contracting plague.

Look For
Chest pain, cough, and sometimes hemoptysis in combination with a history of possible airborne exposure or recent tender, matted regional lymph nodes. Consider plague in any sudden increase in the number of gram-negative pneumonias.

A sudden influx of previously healthy patients presenting with severe pneumonia and/or sepsis, especially in endemic areas and during summer months, should raise the suspicion of possible plague.

Medical Disclaimer:
The information contained in this Web page is intended to be an adjunct to traditional medical information sources. It is not intended to be a substitute for professional medical judgment.

Authors and Editors:
Alex Garza, MD