Plague was first introduced into the United States in 1900, from rat–infested steamships that had sailed from affected areas. Epidemics occurred in port cities. The last urban plague epidemic in the United States occurred in Los Angeles from 1924 through 1925. Plague then spread from urban rats to rural rodent species and became entrenched in many areas of the western United States. Since that time, plague has occurred as scattered cases in rural areas. Most human cases in the United States are acquired in two regions:
Over 80% of United States plague cases have been the bubonic form. In recent decades, an average of seven human plague cases have been reported each year (range: 0–17 cases per year). Plague has occurred in people of all ages (infants up to age 96), though 50% of cases occur in people ages 12–45. It occurs in both men and women, though historically is slightly more common among men, probably because of increased outdoor activities that put them at higher risk.
Since the mid–20th century, plague in the United States has typically occurred in the rural West. Cases in the eastern United States are among people who traveled from the west or from laboratory exposure.
In recent decades, an average of seven human plague cases have been reported each year (range: 0–17 cases per year).
More recent plague epidemics have occurred in Africa, Asia, and South America, but most human cases since the 1990s have occurred in Africa. Almost all of the cases reported in the last 20 years have occurred among people living in small towns and villages or agricultural areas, rather than in larger towns and cities.
