The complications of Yersina pestis infection are dependent on the clinical syndrome (bubonic plague, septicimic plague, pneumonic plague, or pharyngeal plague). Bubonic plague can be complicated by septicemia, pneumonia, or meningitis. The complications of septicemic plague include gangrene of distal upper and lower extremities and tip of the nose due to small vessel thrombosis, disseminated intravascular coagulopathy (DIC), and adult respiratory distress syndrome (ARDS). The complications of pneumonic plague are septicemia, abscess formation, and cavitation. If plague patients are not administered specific antibiotic therapy, the disease can progress rapidly to death. Approximately 14% (1 in 7) of all plague cases in the United States are fatal.

Despite being a treatable disease, plague is still associated with a high case fatality rate, often attributable to late recognition and inappropriate antibiotic therapy. Untreated bubonic plague has a case fatality of rate 50-60%, with proper identification and prompt treatment the case fatality decreases to around 7%.^[3] Untreated septicemia or pneumonic plague is almost universally fatal if untreated early on. Even with proper therapy the latter may lead to mortality rates as high as 50%. ^[4]