Pneumonic plague is both “the least common and most dangerous type of plague,” according to the Cleveland Clinic.

The patient had the pneumonic plague, the rarest and deadliest form of the disease. Human cases remain very uncommon in the United States, though plague is endemic to the western part of the country

Pneumonic plague, a highly contagious and often fatal lung infection caused by Yersinia pestis, recently caused a death in Northern Arizona.