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

FLAGSTAFF, Ariz. — A resident of northern Arizona has died of pneumonic plague, health officials said Friday. Plague is rare to humans, with on average of about seven cases reported annually in the U.S., most of them in the western states, according to federal health officials.