During the pandemic, Candida auris (C. auris), a deadly and highly drug-resistant fungus, saw a "dramatic" rise in cases, according to a new  CDC  study. Now, as the fungus becomes more widespread, health experts are concerned it will continue to evolve and become even more difficult to treat.

What is C. auris?

C. auris was first reported in Japan in 2009, but the earliest strain has been tracked to South Korea in 1996. Since then, it has spread to several different countries worldwide, including the United States, where it was reported in both Illinois and New York in 2016. It can spread through skin or clothing, particularly in healthcare facilities.

The fungus can cause deadly infections in a patient's bloodstream, heart, and brain. Although it is generally not considered dangerous to young, healthy people, it can be dangerous for those who are older or are medically fragile.

According to CDC, around 30% to 60% of patients with C. auris infections have died. However, the agency noted that this information is based on a limited number of patients, and "[w]e don't know if patients with invasive C. auris infection are more likely to die than patients with other invasive Candida infections."

In 2019, CDC identified C. auris as an "urgent threat" in the United States, in part because it is resistant to different classes of antifungal medication. CDC's Antimicrobial Resistance Laboratory Network found that 86% of C. auris samples tested were resistant to a class of drugs known as Azoles. An additional 1.2% were resistant to a frontline treatment class of drugs called echinocandins.

In 2022, World Health Organization (WHO) added C. auris to its fungal priority pathogens list. Hanan Balkhy, WHO's assistant director-general of antimicrobial resistance, said that "fungal infections are growing, and are ever more resistant to treatments, becoming a public health concern worldwide."

The rise of C. auris during the pandemic

In a new study published in the Annals of Internal Medicine, CDC researchers found that there was a "dramatic" increase in C. auris cases and that it spread at an "alarming rate" during the pandemic.

Between 2019 and 2021, annual clinical case counts tripled from 476 to 1,471. Although the paper did not include 2022 data, a CDC website that tracks the fungus shows that there was another sharp increase in 2022, with cases growing to 2,377.

Geographically, C. auris has now spread to half of all U.S. states, with higher concentrations in California, Florida, Nevada, and Texas. According to the researchers, the COVID-19 pandemic likely exacerbated the spread of the fungus since there was less emphasis on screening for C. auris.

In addition, nursing gowns, gloves, and other personal protective gear, which C. auris tends to cling to, were often reused instead of changed frequently as recommended due to supply shortages during the pandemic.

"If [the fungi] get into a hospital, they are very difficult to control and get out," said William Schaffner, a professor of medicine in the infectious diseases division at  Vanderbilt University Medical Center. "They can persist, smoldering, causing infections for a considerable period of time despite the best efforts of the infection control team and everyone else in the hospital."

The researchers also found that treatment-resistant C. auris infections increased during the pandemic. In 2020, there were six pan-resistant and three echinocandin-resistant isolates, which rose to seven pan-resistant and 19 echinocandin-resistant cases in 2021.

"Even this subtle increase is concerning because echinocandins are the first-line therapy for invasive Candida infections and most C. auris infections," the researchers wrote. Although resistance to echinocandin drugs is still relatively rare, there is concern that it will become more common as C. auris continues to evolve, which would make it much more difficult to treat.

However, Meghan Lyman, a medical officer in CDC's mycotic diseases branch and one of the study's authors, noted that there are "a few antifungals in the pipeline [to treat C. auris], so that gives us some hope."

Overall, "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," Lyman said. (Richtel, New York Times, 3/21; Hein, MedPage Today, 3/20; Neukam, The Hill, 3/20; Dreher, Axios, 3/21; Nirappil, Washington Post, 3/20)