The Oregon teen who was hospitalized with bubonic plague last weekend marked the 16th reported case of the illness so far this year in the U.S.
That's already six more cases of the plague than in all of last year, and the numbers have been steadily rising since 2010, when there were only two people in the U.S. diagnosed with the plague, according to the Centers for Disease Control and Prevention. So far this year, three people have died of the illness, and the CDC says it's "unclear" why cases are on the rise.
The teenager from Oregon, who is in intensive care after being hospitalized on Oct. 24, likely caught the plague from an infected flea during a hiking trip, according to a statement from Oregon authorities.
As likely occurred in the Oregon case, the plague is generally transmitted through fleas that pick up the infectious bacterial disease from infected rodents. Plague was responsible for the Black Death that killed almost a third of Europe's population during the 14th century.
The plague first came to the U.S. on rat-infested steamships that arrived in 1900, and the last recorded plague epidemic in the U.S. was in Los Angeles in the 1920s. Since then, cases have been periodically reported, usually in the rural areas in the West and Southwest with large populations of wild rodents.
Symptoms include fever, weakness, chills, and swollen and tender lymph nodes. Some victims will get black pustules. Left untreated, the plague is extremely lethal, with a 66%-93% mortality rate, according to the CDC. But if treated with antibiotics, only about 16% of patients die of the plague.