Bubonic plague has been present in the United States since the beginning of the 20th century but is confined to arid areas in states west of the Mississippi. After an uptick in plague cases (over a dozen) in California in 2015, only 4 cases were reported from New Mexico for 2016. Plague incidence is associated with the rodent population and the number of cases are affected by environmental factors. Plague is typically transmitted to humans by the bite of a rat flea. In a typical year, reported cases in the US are in the single digits.
The world hotspot for bubonic plague is currently the island of Madagascar which has had sporadic outbreaks amounting to about 7000 cases in the past 10 years. Plague that goes untreated has about a 60% mortality rate but that falls to less than 20% if treated with proper antibiotics.