The fungus Candida auris, which causes a highly infectious and potentially deadly infection, is spreading faster in U.S. health care facilities and likely becoming more resistant to treatments, a new study shows.
C. auris is a fungal species of yeast that can infect humans and spread in the blood to major organs. The infection occurs most often in healthcare settings and long-term care facilities and is rare in healthy individuals. But for people who are immune compromised or receive regular invasive treatments for other illnesses, it can often be fatal.
The first C. auris infection was documented in Japan in 2009 and the fungus has since been found in many other countries, including the U.S., which had its first confirmed case in 2016. The disease made headlines back in 2019 when the number of cases began to sharply climb worldwide, and it still "presents a serious global health threat" today, according to the Centers for Disease Control and and Prevention (CDC).
In the new study, published March 21 in the journal Annals of Internal Medicine, researchers conducted a new assessment of C. auris cases recorded in the U.S. between 2019 and 2021. In total, 10,683 cases were recorded during this period: 3,270 of the cases were clinical infections, meaning the patient showed symptoms before being tested, and 7,413 cases were screening colonizations, meaning that people carried the fungus but showed no symptoms before being tested during routine screening. People carrying the fungus can still spread the pathogen, and they may develop symptoms of illness later on.
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The number of clinical infections increased year on year during the study period. In 2019 there was a 44% increase compared with 2018; in 2020 there was a 59% spike compared with 2019; and in 2021 there was a 95% surge compared with 2020. (The study did not include data on the number of fatalities among clinical infections.)
This shows that the rate of transmission is likely increasing, study lead author Dr. Meghan Lyman, a medical officer at the CDC, told Live Science in an email. "The number of cases has continued to increase since 2021," she added.
The number of screening colonizations also increased significantly during the study period. But this is partially due to an increase in the number of screening tests. In 2019, there were 19,756 tests conducted nationwide, but in 2021, there were more than 40,000 tests. This suggests that the number of colonizations could be underreported due to a lack of screening tests, which could be helping the disease to spread, Lyman said.
The number of states that have recorded C. auris cases has also increased, from 10 states in 2018 before the study began to 27 states in 2021.
Another key finding of the new study is that C. auris is becoming increasingly resistant to treatments.
"There are only three main classes of antifungal medications used to treat Candida infections: azoles, polyenes and echinocandins," Lyman said. A majority of C. auris cases are resistant to azoles and a high percentage are also resistant to polyenes. But the number of cases of echinocandin-resistant C. auris has remained very low and, as a result, echinocandins have become the preferred treatment option for C. auris, Lyman said.
However, the number of echinocandin-resistant cases has increased in recent years. Six cases were reported between 2016 and 2019, another six cases were reported in 2020, and 19 were reported in 2021, which suggests the fungus is slowly becoming more resistant to this treatment. But new antifungals are in the early stages of being developed to help treat future infections, Lyman said.
Since C. auris is mainly transmitted in hospitals and other healthcare settings, researchers suspect that the effects of the COVID-19 pandemic may have played a role in the fungus' spread.
"Gaps in case detection and infection control existed before the COVID-19 pandemic, but pandemic-related strain on the health care and public health systems likely contributed to [increased] transmission," Lyman said.
However, for healthy people who are not regularly exposed to a healthcare setting, the risk of being infected or colonized by C. auris remains "low," Lyman said. But increased screening and better transmission control in healthcare settings are needed to keep the fungus under control, she added.
