Climate Change Likely Why Dangerous Fungus Spreading Fast, Scientists Say

SEATTLE — In 2016, hospitals in New York state identified a rare and dangerous fungal infection never before found in the United States. Research laboratories quickly mobilized to review historical specimens and found the fungus had been present in the country since at least 2013.

In the years since, New York City has emerged as ground zero for Candida auris infections. And until 2021, the state recorded the most confirmed cases in the country year after year, even as the illness has spread to other places, according to Centers for Disease Control and Prevention data analyzed by The Associated Press.

Candida auris is a globally emerging public health threat that can cause severe illness, including bloodstream, wound and respiratory infections. Its mortality rate has been estimated at 30% to 60%, and it’s a particular risk in health care settings for people with serious medical problems.

Last year, the most cases were found in Nevada and California, but the fungus was identified clinically in patients in 29 states. New York state remains a major hot spot.

A prominent theory for the sudden explosion of Candida auris, which was not found in humans anywhere until 2009, is climate change.

Humans and other mammals have warmer body temperatures than most fungal pathogens can tolerate, so they have historically been protected from most infections. However, rising temperatures can allow fungi to develop tolerance to warmer environments, and over time humans may lose resistance. Some researchers think this is what is happening with Candida auris.

When Candida auris was first spreading, said Meghan Marie Lyman, a CDC medical epidemiologist for the mycotic diseases branch, the cases were linked to people who had traveled to the U.S. from other places. Now, most cases are acquired locally — generally spreading among patients in health care settings.

In the U.S., there were 2,377 confirmed clinical cases diagnosed last year — an increase of more than 1,200% since 2017. But Candida auris is becoming a global problem. In Europe, a survey last year found case numbers nearly doubled from 2020 to 2021.

“The number of cases has increased, but also the geographic distribution has increased,” Lyman said. She noted that while screenings and surveillance have improved, the skyrocketing case numbers reflect a true increase.

In March, a CDC press release noted the seriousness of the problem, citing the pathogen’s resistance to traditional antifungal treatments and the alarming rate of its spread. Public health agencies are focused primarily on strategies to urgently mitigate transmission in health care settings.

Dr. Luis Ostrosky, a professor of infectious diseases at McGovern Medical School at UTHealth Houston, thinks Candida auris is “kind of our nightmare scenario.”

“It’s a potentially multidrug resistant pathogen with the ability to spread very efficiently in health care settings,” he said. “We’ve never had a pathogen like this in the fungal infection area.”

Ostrosky has treated about 10 patients with the fungal infection but has consulted on many more. He said he has seen it spread through an entire ICU in two weeks.

The fungus poses a significant threat to human health, researchers say.

Immunocompromised patients in hospitals are most at risk, but so are people in long-term care centers and nursing homes, which generally have less access to diagnostics and infection control experts.

Candida auris is not only challenging to treat, but also difficult to diagnose. It is rare and many clinicians are not aware it exists.

Beyond the increase in cases, popular culture has helped increase awareness of fungal infections. A popular HBO series, The Last of Us, is a drama about the survivors of a fungal outbreak.

“I think the way to think about how global warming is putting selection pressure on microbes is to think about how many more really hot days we are experiencing,” said Arturo Casadevall, a microbiologist, immunologist and professor at Johns Hopkins University. “Each day at (37.7 degrees Celsius) provides a selection event for all microbes affected — and the more days when high temperatures are experienced, the greater probability that some will adapt and survive.”