Scary stuff. A man had a dog that most likely caught a plague from fleas from either an infected prairie dog or rabbit. The disease was passed to the owner and then 3 other people who came in contact with the dog. 3 of the 4 people who contracted the disease had the disease progress to the pneumonic plague, which is transmittable person to person.
Three more cases of rare human plague found in Colorado | Reuters Three more cases of plague identified in Colorado - The Denver Post