Human plague, caused by Yersinia pestis, is transmitted by exposure to rodents, particularly through bites of rodent fleas. It is endemic in the Western U.S. This life-threatening infection presents in three forms, bubonic (roughly 85% of cases), septicemic (10%), and pneumonic (3%). Person-to-person transmission is rare but can occur following exposure to patients with pneumonic plague. Over the last decade, a median of three cases have been reported each year in the U.S. (range, 1–17). Aggressive antibiotic treatment (aminoglycosides, fluoroquinolones, or doxycycline) reduces mortality considerably.

The CDC has received reports of 11 cases of human plague since April 2015. The exposures occurred mostly in residents of Western states (Arizona, California, Colorado, Georgia, New Mexico, and Oregon). Two cases occurred following exposures at Yosemite National Park in California. Nine patients were male; age ranged from 14 to 79 years. Three patients died, including a 16-year-old. The authors caution about the risk of contact with rodents.

After the CDC report was published, the Utah Department of Health reported a new fatal case in an elderly resident, bringing the total number of fatal cases in the U.S. this year to four.