A drug-resistant and potentially deadly fungus has been spreading rapidly through U.S. health care facilities, a new government study finds.

The fungus, a type of yeast called Candida auris, or C. auris, can cause severe illness in people with weakened immune systems. The number of people diagnosed with infections — as well as the number of those who were found through screening to be carrying C. auris — has been rising at an alarming rate since it was first reported in the U.S., researchers from the Centers for Disease Control and Prevention reported Monday.

The increases, “especially in the most recent years, are really concerning to us,” the study’s lead author, Dr. Meghan Lyman, chief medical officer in the CDC’s Mycotic Diseases Branch, said in an interview. “We’ve seen increases not just in areas of ongoing transmission, but also in new areas.”

The CDC's new warning, published in the Annals of Internal Medicine, comes as the Mississippi Department of Health is fighting a growing outbreak of the fungus. Since November, at least 12 people have been infected with C. auris with four "potentially associated deaths," the state's epidemiologist Dr. Paul Byers, said in an email.

There has been ongoing transmission at two long-term care facilities, although cases have been identified at several other facilities in the state.

"Unfortunately, multi-drug resistant organisms such as C. auris have become more prevalent among our highest risk individuals, such as residents in long-term care facilities," Byers said.

The fungus can be found on the skin and throughout the body, according to the CDC. It's not a threat to healthy people, but about one-third of people who become sick with C. auris die.

In the CDC report, researchers analyzed state and local health department data on people sickened by the fungus from 2016 through Dec. 31, 2021, as well as those who were “colonized,” meaning they were not ill but were carrying it on their bodies with the potential of transmitting it to others who might be more vulnerable to it.

The number of infections increased by 59%, to 756, from 2019 to 2020 and then by an additional 95%, to 1,471, in 2021.

The researchers also found that the incidence of people not infected with the fungus but colonized by it increased by 21% in 2020, compared to 2019, and by 209% in 2021, with an increase to 4,041 in 2021 compared to 1,310 in 2020.

C. auris has now been detected in more than half of U.S. states, the new study found.

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