A 58-year-old man in New Mexico was recently treated for bubonic plague, the first case of the disease formerly known as "Black Death" to surface in 2011.
Health officials in Santa Fe said the unidentified man spent a week in the hospital after suffering high fever, intense pain in his stomach and groin and swollen lymph nodes.
He was treated and released, but officials would not say when.
The results of blood tests released Thursday confirmed the man had bubonic plague, officials said.
Doctors said the man was most likely bitten by a flea carrying the plague bacteria, the most common method of transmission to humans.
Rat-borne fleas can carry the bacterium, and humans can also catch the disease from contact with infected rodents or animals.
"He was probably bitten by a flea somewhere on his left leg," Department of Health veterinarian Paul Ettestad told the Santa Fe New Mexican.
Officials wouldn't say where the man lived, but said they would check his home for rats and rodent burrows and alert his neighbors, the paper said.
Only about 10 to 15 people in the United States catch the frightening illness each year, typically in western states. It is particularly prevalent in New Mexico because the state has a high population of both rodents and fleas.
Globally, health officials report about 1,000 to 3,000 cases per year, according to the Centers for Disease Control.
Symptoms include fever, chills, headeache, weakness and swollen nodes in the neck, armpit or groin.
It can be treated with antibiotics, but 1 in 7 cases are fatal.
The last reported outbreaks of plague in New Mexico were in 2009, when three people, including an 8-year-old in Santa Fe, died.
The disease became known as the Black Death when it famously swept through Europe in the 14th century, killing an estimated 75 million people.