It's not a fungus apocalypse. But it's a serious, growing problem.

The Centers for Disease Control and Prevention (CDC) announced this week that the fungus Candida auris (C. auris) "spread at an alarming rate in U.S. healthcare facilities" during 2020-2021. This fungus is particularly problematic because it's a strain that has emerged in recent years, can be resistant to some, or all, antifungal drugs, and has caused outbreaks in hospitals, Dr. Luis Ostrosky, an M.D., fungal infection expert, and professor of infectious diseases at UTHealth Houston, recently told Mashable.

The CDC is taking the spread, which can cause severe and fatal blood infections, seriously.

"The rapid rise and geographic spread of cases is concerning and emphasizes the need for continued surveillance, expanded lab capacity, quicker diagnostic tests, and adherence to proven infection prevention and control," CDC epidemiologist Dr. Meghan Lyman, lead author of the new research, said in a statement.

The research, entitled, "Worsening Spread of Candida auris in the United States, 2019 to 2021," is published in the medical journal Annals of Internal Medicine.

How worried should you be about Candida auris?

The fungus Candida auris, which is a yeast, infects people who are quite ill and have compromised immune systems.

"To experience a fungal infection, there has to be something wrong with your immune system," Dr. Ostrosky, who is also chief of epidemiology at the academic hospital Memorial Hermann, explained. This includes people who have had organ transplants or other major, life-saving surgeries, as well as those undergoing cancer treatments, he said.

People in hospitals who are unwell are particularly susceptible to Candia auris. "People who are very sick, have invasive medical devices, or have long or frequent stays in healthcare facilities are at increased risk for acquiring C. auris," the CDC said.

Fortunately, like with most fungal spores, healthy people are not the group being infected or at risk. "In general, C. auris is not a threat to healthy people," the agency noted. That's because our advanced, healthy immune systems constantly combat fungal spores, and keep such foreign fungi microbes at bay. (For example, we inhale fungal spores every time we go outside.) "Humans are really, really good at staving off fungal infections," Vincent Bruno, a scientist at the Institute for Genome Sciences at the University of Maryland School of Medicine who researches fungal diseases, told Mashable this year.

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But for those infected with Candia auris, the CDC is raising the alarm because it's often resistant to multiple antifungal drugs that doctors use to treat Candida infections. Candida auris is a newly emerged strain of the fungus Candida, which already causes some 25,000 infections annually. Some 30 to 60 percent of people infected with C. aurishave died, the CDC said. "However, many of these people had other serious illnesses that also increased their risk of death," the agency noted.

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How much is Candida auris spreading?

Since 2016, the CDC has been increasingly concerned about Candida auris. That's when the health agency received reports that the fungus was resistant to medicines in other parts of the world.

"It seemed hard to believe," the CDC wrote. "CDC fungal experts had never received a report describing a Candida infection resistant to all antifungal medications, let alone Candida that spreads easily between patients."

• Reported cases, though overall low in numbers, have been rising significantly since 2015. Cases increased 318 percent in 2018, compared to the previous few years, resulting in a total of 323 clinical cases.

• Crucially, Candida auris cases have only increased each year since 2016. "Nationwide, clinical cases rose from 476 in 2019 to 1,471 in 2021," the CDC just concluded.

• Case counts again increased in 2022, the agency noted.

  Counts of reported Candida auris cases in the U.S. in 2022.Credit: CDC

A number of factors may contribute to these rising numbers, the agency notes. This includes poor infection control, more screening to detect the infection (a good thing), and increased fungal spread during a time of great strain on the healthcare system during peaks of the COVID pandemic hospitalizations.

To limit the spread, the CDC is sounding the alarm to aid healthcare facilities in identifying the infectious fungus, and how to contain the microbe in places like hospitals and nursing homes.

This story was originally published on March 21, and has been updated with more information about Candida auris.