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For the first time ever, researchers have reported cases of people carrying or infected with strains of the dangerous fungus Candida auris that were resistant to all major classes of antifungal drugs before any treatment, the Centers for Disease Control and Prevention said Thursday. The agency also reported evidence of some transmission of the strains within health facilities.

Candida auris, or C. auris, which was first seen in 2009, has been highly resistant to the few available treatment options for several years, leaving people who treat and study fungal diseases concerned about the toll this superbug could take, particularly on severely ill patients. That there are now so-called pan-resistant cases in people who had never been treated with antifungal drugs is particularly unnerving, experts said.

The CDC reported on five cases, three in Washington, D.C., and two in Texas. In both locations, the cases were clustered within facilities. The facilities were not identified, but the fungus is most commonly diagnosed in very sick people who are in specialized long-term facilities.

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There was no known link between the Washington and Texas cases. The cases were outlined in the CDC’s online journal Morbidity and Mortality Weekly Report.

Pan-resistant C. auris was first detected in 2019 in people who developed resistance while being treated with antifungal drugs. What makes these newly reported cases more concerning is the fact none of the people had been treated with antifungal drugs prior to the diagnosis. That means the strain of C. auris they caught was already pan-resistant.

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“This is the first time that we’ve actually identified clusters with common health care exposures in the same facilities and among patients who had not received antifungals,” Meghan Lyman, a medical officer in the mycotic (fungal) diseases branch in CDC’s National Center for Emerging and Zoonotic Infectious Diseases, told STAT in an interview.

There are only three classes of antifungal drugs used for treating Candida auris infections — azoles, polyenes, and echinocandins. Most C. auris cases detected in the United States are resistant to azoles (85%) and many are resistant to polyenes (38%). The overwhelming majority (99%) have been susceptible to echinocandin drugs, so they are the first-line therapy when C. auris is detected.

These pan-resistant cases raise questions about how long and how well the first line will hold.

“These cases are ones where the options are really limited. There are few treatment options for these patients who have clinical infections. And the fact that now it can spread, it’s not just in patients who are already getting treatment … means that a greater proportion of patients may have pan-resistance and [may] develop clinical infections that are potentially untreatable,” Lyman said.

In the Texas outbreak, in addition to the two pan-resistant cases, there were five patients with C. auris that was resistant to both echinocandins and fluconazole, an antifungal drug in the azole class. The seven were detected in two different facilities, but there was movement of patients between the two institutions.

The 30-day fatality rate among the patients in both the Texas and Washington outbreaks was 30%, but because these people were all severely ill, it isn’t possible to say whether the C. auris infections caused or contributed to their deaths.

In some of cases, C. auris was found on the skin of people; in epidemiological terms, they were “colonized.” In that state, the fungus isn’t causing disease, but people who are colonized can spread the fungus to other patients and may eventually go on to have active infections themselves. Lyman said between 5% and 10% of people found to be carrying C. auris will go on to have active or “invasive” infections later.

Though this report deals with a mere five cases, it’s likely there are more, Lyman said. The Covid-19 pandemic has siphoned off surveillance capacity for other pathogens; even before the pandemic, surveillance for drug-resistant fungal infections was spotty.

“It might be under-detected. That’s very likely,” she said.

Despite the inadequacy of surveillance, researchers say the pandemic has fueled an increase in C. auris cases. A number of people who become severely ill with Covid require care in the types of facilities where these fungal infections are being found.

“We tend to see transmission and see cases among patients who are in these high-acuity, long-term care facilities … that have very high-acuity, very sick patients like ones who are on ventilators or have tracheostomy or other invasive medical devices,” Lyman said. “Getting Covid and then having these complications put them at higher risk for acquiring Candida auris.”

Facilities treating these kinds of patients should be on high alert for C. auris, she said, because finding it quickly is key to containing it.

“With all this spread that we’ve been seeing across the country we’re really encouraging health departments and facilities to be more proactive instead of reactive to identifying Candida auris in general. Because we’ve found that controlling the situation and containing spread is really easiest when it’s identified early before there’s widespread transmission.”

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