Just five months after federal health officials asked hospitals and physicians to be on the lookout for an often-fatal, antibiotic-resistant fungus called Candida auris, 13 cases have been reported, the Centers for Disease Control and Prevention announced Friday. It is the first time that the fungus, which is easily misidentified in lab tests as a more common candida yeast infection, has been found in the US, and four of the first seven patients with it have died.

“We need to act now to better understand, contain and stop the spread of this drug-resistant fungus,” the CDC’s director, Dr. Thomas Frieden, said in a statement. “This is an emerging threat, and we need to protect vulnerable patients and others.”

C. auris’s emergence and apparent global spread — it was first identified in Japan in 2009 and since then has been found in a dozen countries on four continents — put the pathogen on the ever-growing list of superbugs, disease-causing microbes that are resistant to many and, in some cases, all antibiotics.

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The first seven cases, which are described in the CDC’s Morbidity and Mortality Weekly Report, occurred in New York, Illinois, Maryland, and New Jersey in 2013 (one case), 2015 (one case), and this year (five cases). The older cases were identified through a review of patients’ lab records conducted after the CDC sent its clinical alert in June. All seven of the patients had been hospitalized for cancer, respiratory failure, or other serious condition, so it is not clear if C. auris contributed to the deaths of four of them, the CDC said.

The other six cases came to the CDC’s attention after August.

Five of the first seven cases had not been flagged as C. auris at the time the patients were hospitalized, underlining the difficulty of identifying the fungus. Five were also resistant to the common antifungal drug fluconazole (sold as Diflucan). One was resistant to amphotericin B, an antifungal usually saved for serious infections, and one to echinocandins, a newer class of antifungals touted as being effective against Candida.

Although C. auris strains from other countries have been found to be resistant to all three major classes of antifungal drugs, none of the US cases was.

The global spread of C. auris has had public health officials on alert for imported cases, but all of the US cases seem to have been contracted domestically. When scientists sequenced the genomes of C. auris in the first seven cases, they found that they were related to strains from South Asia and South America. Since none of the patients had traveled to those areas or were known to have been in contact with anyone from there, CDC scientists concluded that they had acquired the infections locally.

“It appears that C. auris arrived in the United States only in the past few years,” Dr. Tom Chiller, who leads CDC’s Mycotic Diseases Branch, said in a statement. “We’re working hard with partners to better understand this fungus and how it spreads.”

A partial answer: easily. After one of the Illinois patients was hospitalized for an unrelated illness, researchers found C. auris in his mattress, bedside table, bed rail, chair, and windowsill.

More evidence of how easy C. auris is spread, at least in hospitals: The genome sequencing showed that the two patients treated in the same New Jersey hospital at the same time had nearly identical strains; the genome sequences of the C. auris infecting the two Illinois patients, also treated at the same hospital at the same time, were also nearly identical to one another. “These findings suggest that C. auris could be spread in healthcare settings,” the CDC said.

Although 60 percent of people with C. auris infections outside the US have died, the CDC said, that figure is based on a small number of patients, many of whom had other severe illnesses, making it unclear how serious the infection on its own might be.