Climate change seems to be making it easier for pathogens to pose risks to our health. A recent entrant is Candida auris, an emerging fungus that was first reported in the US in 2016.
The Centers for Disease Control and Prevention (CDC) deems it an “urgent threat” mainly because many strains of the yeast are already resistant to all available treatments, it spreads rapidly in healthcare settings, and it can be fatal. And its reach is quickly spreading, with a recent CDC study reporting the number of known cases nearly doubled in 2021 to 1,471 — and that’s likely an underestimate.
Candida auris is a particular concern because, unlike most fungi, it can spread person to person, said Dr. Scott Roberts, associate medical director of infection prevention at Yale School of Medicine.
“Current C. auris trends are quite worrying and require a nationwide call to action,” said Dr. Syra Madad, an infectious disease epidemiologist at Harvard's Belfer Center for Science and International Affairs and the New York City Hospital System.
The emergence of different clades, or distinct families, of C. auris and their rapid spread around the world are likely due to climate change, Madad said. “Global warming, for example, may be leading to better adaptation of C. auris to higher temperatures and ultimately greater susceptibility of infection to humans.”
When organisms like fungi evolve to live at higher temperatures, it can give them an advantage when it comes to growing in the high-temperature conditions of the human body.
What is Candida auris?
First identified in Asia in 2009, C. auris is now found on four continents. In the US, it was initially only found in certain hospitals, nursing homes, and long-term healthcare settings in a few major hubs like New York City and Chicago, Roberts said. But a recent CDC study showed that it has now been found in more than half of US states.
This type of yeast can colonize your skin and gut, among other areas. It’s spread by close contact with someone who is infected or colonized with the fungus. The person does not need to have symptoms to be infectious, Roberts said. It can also spread through contaminated surfaces, where it can survive for weeks, according to the CDC.
The only treatment is intravenous antifungal medications, but the recent CDC report, published in Annals of Internal Medicine, documented a tripling in the number of cases resistant to echinocandins, the class of drug that is typically the first choice for this type of infection.
Some isolates are resistant to three major classes of available antifungal medications and most are resistant to fluconazole (Diflucan), one of the most common antifungals out there, Roberts said.
In absolute numbers, though, drug-resistant cases are still relatively uncommon.
Who’s at risk?
Many times, C. auris doesn’t cause any infection, Roberts said. But not always.
“Those at highest risk for severe infections with C. auris include people who are already sick from other health conditions and are immunocompromised, have long or frequent stays in healthcare facilities, or have lines or tubes that go into their body, such as central venous catheters, feeding tubes, breathing tubes,” Madad said. “The infection can prove deadly for 30% to 60% of those infected with invasive C. auris.”
Why it’s spreading
A warming climate is likely a major reason for the rapid rise in C. auris around the world.
“A major hypothesis as to why this wasn’t seen before is that this fungus evolved with climate change,” Roberts said. “It is better able to withstand higher temperatures compared to similar types of fungi.”
But the CDC has also identified other reasons for the increase in cases, including higher screening rates, a healthcare system that’s under pressure due to the COVID-19 pandemic, and insufficient infection control procedures.
Healthcare facilities and public health experts are at the forefront of fighting the germ and must increase surveillance and take steps to control infections in general, the experts we talked to said.
The most important steps people can take to avoid the fungus is to practice good hand hygiene, aka hand washing, especially in healthcare settings, Roberts said.
Other emerging threats
Roberts predicted that we’ll see more pathogens emerge as global temperatures continue to rise. “Climate change is going to increase the risk of new fungal threats, and Candida auris is a great example,” he said. “I suspect over time we will see both rising cases of Candida auris and new species emerge.”
The World Health Organization released its first “fungal priority list” late last year, which put pathogens into “critical,” “high” and “medium priority” categories. Candida auris is on the critical list, as are Candida albicans (also a yeast), Cryptococcus neoformans (which can infect the lungs and central nervous system), and Aspergillus fumigatus (which has developed resistance to certain drugs).
“While C. auris outbreaks are not indicative of [a scenario like] the HBO hit show The Last of Us — and far from it — the reality is, as climate change persists, its impact on infectious diseases ... will only grow,” Madad said.