First Cases of Drug-Resistant Ringworm Found in the U.S.

The two patients—both in New York City—developed itchy rashes that did not go away with typical antifungal medications

Fungus under a microscope
Trichophyton simii, shown here under a microscope, is one of 40 species of fungi that can cause ringworm infections. CDC / Dr. Kaplan

A drug-resistant fungus that causes ringworm infections has spread to the United States, with at least two cases identified in New York City in the last two years, according to a new report from the Centers for Disease Control and Prevention (CDC).

Public health officials urged doctors to be on the lookout for ringworm infections, also known as tinea, that do not respond to traditional first-line treatments.

The two recent New York City infections stemmed from a species of fungus named Trichophyton indotineae. Though infections caused by T. indotineae have been on the rise in South Asia during the last ten years—likely due to the overprescription and misuse of antifungal medications, according to the CDC—these are believed to be the first reported cases in the U.S. It’s also spread throughout Asia and to Canada and Europe, per the agency.

Contrary to what its name suggests, ringworm is not caused by worms, but by more than 40 different species of fungi, per Gizmodo’s Ed Cara. Symptoms include a ring-shaped rash, hair loss and itchy, red, scaly or cracked skin, per the CDC. The rash can form anywhere the fungus comes in contact with the body, but it commonly occurs on the feet, scalp, groin or beard areas. These signs typically show up within four to 14 days of exposure. Historically, ringworm infections have been relatively mild and easy to treat with antifungal creams.

Fungi tend to thrive in warm, moist conditions, so doctors should pay extra close attention to any drug-resistant ringworm infections as the temperatures start to heat up this summer, as Priya Soni, a pediatrician who specializes in infectious diseases at Cedars-Sinai Medical Center and was not involved in the report, tells CNN’s Jen Christensen.

“With globalization and just the travel that we’re going to see over the summer, this may be something that we may see more of as the months go on,” Soni tells CNN.

One of the two U.S. cases was a 47-year-old woman who developed a bad rash while traveling in Bangladesh last summer. While there, she applied antifungal and steroid topical creams to the rash, but it didn’t get any better. When she returned to the United States, she went three separate times to an emergency room for relief from the ringworm. Again, doctors prescribed her several antifungal and steroid creams, but they did nothing to curb the rash.

Eventually, in December 2022, she visited dermatologists who tried a new strategy—they prescribed her a month-long course of oral antifungal medication known as terbinafine. When her symptoms again failed to improve, they tried another antifungal medicine called griseofulvin. Finally, roughly 80 percent of the rash went away.

Avrom Caplan, a dermatologist at the NYU Grossman School of Medicine, treated the patient and soon grew concerned that the fungus did not respond to typical medications. He asked fellow doctors to see if any had recently encountered anyone with similar symptoms. During the course of his investigation, he learned about a 28-year-old woman in New York who had not traveled out of the country but had developed a bad case of ringworm in the summer of 2021. Together, the two cases provided enough cause for concern to alert public health officials, and Caplan was the lead author on the CDC’s new report.

T. indotineae joins a growing list of drug-resistant superbugs spreading around the country and the world. In March, CDC-affiliated researchers published a paper about the rapid spread of another drug-resistant fungus, Candida auris, which is particularly harmful to certain vulnerable populations. That study came on the heels of a February World Health Organization report that warned of the growing prevalence—and threat—of antimicrobial-resistant superbugs.

Though much of the medical focus has been on drug-resistant bacteria, the two New York cases of T. indotineae are a good reminder that fungi are just as capable of evolving to overcome treatments, experts say.

“We’re always so focused on antimicrobial resistance as it relates to bacteria that we forget that those rules also apply to fungi,” says Adam Friedman, a dermatologist at George Washington University who was not involved with the CDC report, to NBC News’ Erika Edwards.

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