Reported cases of human plague infections in the United States, 1970-1991.

From 1970 to 1991, 295 indigenous cases and one imported case of human plague were reported in the United States. Eighty-two percent of the total indigenous cases occurred in New Mexico, Arizona, and Colorado. Ninety-three percent of these cases had onset in the months of April through November. Most cases (89%) presented as bubonic or septicemic plague, or both. Cases were reported more frequently in males (58%), and male mortality exceeded that of females (17 versus 11%). Ground squirrels were the most frequently implicated sources of infection in cases associated with flea bites, and domestic cats were found to play an increasingly important role in transmission of disease to humans during these decades.