By Jen Christensen, CNN

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The US Centers for Disease Control and Prevention is reporting the first known cases of an antifungal-resistant ringworm in the United States and urging providers to be on the lookout for such infections.

The details of the cases were reported to the CDC in February and shared in a report published Thursday. The patients – two unrelated women in New York City – first had symptoms in 2021 and 2022. One patient had no international travel history, suggesting that there is some community spread in the US.

Despite the name, ringworm is not caused by a worm; rather, it is caused by one of 40 species of fungus. In this case, the infections were caused by Trichophyton indotineae, a recently discovered fungus.

Cases were first concentrated in patients in South Asia, but they’ve now also been found in countries in Europe. These are the first known US cases.

Ringworm can take several forms but often causes what looks like a superficial skin rash that forms a ring around otherwise normal-looking skin. It is a highly uncomfortable and itchy rash.

In the case of the first patient, the 28-year-old woman seemed to develop the rash in the summer of 2021. She went to see a dermatologist in December and said she had not traveled internationally, nor had she any known exposures to someone with a similar rash.

The report says the woman had “large annular, scaly, pruritic plaques” over her neck, stomach, pubic region and buttocks. Doctors put her on an oral therapy that she started taking in January 2022.

When the rash did not improve after two weeks of terbinafine, a common antifungal, doctors put her on itraconazole, a liquid medicine that’s typically used to treat yeast infections in the mouth and throat. It seemed to work, and the infection cleared up after the woman took the medication for four weeks. Doctors are still monitoring her, because ringworm infections can return.

The second patient, a 47-year-old woman, developed the rash on her thighs and buttocks while visiting Bangladesh in the summer of 2022. Doctors there treated her with a topical antifungal and steroid creams, but the rash did not seem to clear up. Several other family members in Bangladesh also developed similar rashes.

In the fall, when the woman was back in the US, she went to the emergency room three times for help. Doctors gave her several creams and treatments typically used for ringworm, but by December, dermatologists noted that there was no improvement.

She was also given oral terbinafine, but her symptoms didn’t improve. Things got better after she was treated with a four-week course of griseofulvin, a medication also often used to treat athlete’s foot and fungal infections on the scalp, but doctors are looking into other treatment options. Her son and husband, who live with her, are undergoing evaluation for similar infections.

Dr. Priya Soni, a pediatric infectious disease specialist at Cedars-Sinai Medical Center in Los Angeles, said it’s impressive that physicians were able to get the species identified with the help of their public health department.

Because one of the patients had no history of travel to any area that has seen cases, she said, it’s a real signal that there’s been some epidemiological changes within the fungal species.

“It may also be a little more widespread than we have noted before, so for physicians and other providers, I think it’s important to be aware that we may be seeing more of this particular species as we go into the warmer, moist summer months,” said Soni, who was not involved with either new case. “I think 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.”

The report encourages providers to be on the lookout for these infections. Soni said one red flag would probably be if someone with a rash does not respond to terbinafine after about four weeks of treatment.

The CDC urges health-care providers to contact their state or local public health department if a rash does not respond to first-line treatments so the cases can be further tested; it notes that testing techniques used by most clinical labs typically misidentify cases of this ringworm as other types.

Although itraconazole seemed to work when the first-line treatments didn’t, it can be difficult to absorb and doesn’t always interact well with other medications. It can also take up to 12 weeks to work.

“Antimicrobial stewardship efforts are essential to minimize the misuse and overuse of prescribed and over-the-counter antifungal drugs and corticosteroids,” the report says.

The CDC also encourages doctors to educate patients about how to prevent the spread of ringworm.

Soni said she would advise people to not share clothes, combs or hats with people who have a rash and to avoid close contact with those who have ringworm.

Because fungi like warm, moist environments, dry your feet well between taking a shower and putting on socks and shoes.

Good hand hygiene can also help, since the fungal infection is spread skin to skin. The fungus can be found in soil, so it’s important to wear gloves or wash hands well after gardening or digging in the dirt.

People can get ringworm after petting a farm animal or even a dog or cat that has an infection.

“Any kind of ringworm really flourishes in the warm, moist weather, especially in locker rooms, indoor pools, that kind of thing,” Soni said.

With the world growing warmer and wetter, scientists say we’ll probably see more fungal infections like this. The concern, of course, will be that even more will be resistant to mainstay treatments.

“We run into a little bit of a problem when you see new species that are intrinsically resistant to some of our more common antifungals,” Soni said.