A second person has died from the plague in Colorado.
The Pueblo City-County Health Department said in a press release that "the individual may have contracted the disease from fleas on a dead rodent or animal."
A dead prairie dog in the western part of Pueblo County is the only animal confirmed to have the plague in the immediate area.
"This highlights the importance to protect yourself and your pets from the exposure of fleas that carry plague," said Sylvia Proud, the city-county public health director.
It's the first such case of someone in Pueblo County contracting the plague since 2004.
While cases of the plague in humans are exceptionally rare in the US, about seven reported each year on average.
In 2014, eight cases were reported in Colorado alone. The latest death brings the death toll up to two in 2015.
In May, a sick Colorado pit bull infected its master, two veterinarian workers and possibly also a friend of the owner with plague. The case was unique because it was the first time a dog had been identified as a source of human plague in the US. It's also the first possible human-to-human transmission since an outbreak in Los Angeles in 1924.
In June, a 16-year-old passed away in Larimer County. Health officials were only able to establish that he had suffered from septicemic plague after his death.
It is understood that the latest victim in Pueblo County had a similar type of the disease.
Of 17 cases reported between 2005 and 2015, none were in Pueblo County.
The CDC says about seven people get the plague - over 80% of which have been in the bubonic form - every year in the United States. While it can be life-threatening, with modern medicine such as antibiotics and antimicrobials it is usually not deadly, as it was in the Middle Ages when millions died.
The Yersinia pestis bacteria, that causes Bubonic plague, is passed along in flea bites. The pneumonic form, that infects the lungs, can either be a complication of Bubonic plague or transmitted directly by cough droplets. It's the most dangerous form of plague because it can spread in the air, and it's the only way plague is transmitted from human to human.
An investigation into the latest death is continuing, and Pueblo County residents are being urged to report any unusual instances of rabbits and prairie dogs "dying off".