According to the Centers for Disease Control and Prevention, there are 5 to 15 reported cases of bubonic plague in the US every year, and 1 in 7 is fatal. As you can see, they are not randomly distributed. Plague lives most of the time in communal, ground-dwelling rodents like prairie dogs. You can get it from handling prairie dogs, or being bitten by a flea from a prairie dog, but more often it has first spread to some other rodent community, such as grasshopper mice. In 1924 there was an outbreak in Los Angeles that killed 37 people, and in that case the bacillus had somehow spread to rats.
In today's really bad news, a form of plague resistant to most antibiotics has been reported in Madagascar.