Authorities are trying to get a handle on a new fungal infection that is sometimes fatal after 13 people fell ill from such a disease for the first time in the United States, according to a report from the Centers for Disease Control and Prevention. The fungus is called Candida auris, and is known to occur in hospitals and nursing homes, however it hadn’t yet been seen in the U.S., an alarming development.

A total of seven cases were reported between May 2013 and August 2016 in Illinois, Maryland, New Jersey and New York, and four of those patients died with bloodstream infections, although authorities couldn’t confirm that C. auris was the cause. Another six cases have been identified since August, and those are under investigation.

Scientists have found that C. auris bloodstream infections have a 50 percent fatality rate in some countries, although it’s unclear how potent this drug resistant infection would be in the U.S.

“In two separate circumstances, two patients were hospitalized in the same hospital,” the CDC statement reads. “The first instance included the two patients from Illinois who were admitted to the same hospital on three separate occasions but were on different floors or wings of the hospital. These two patients were subsequently also admitted to a long-term acute care hospital within days of one another, although their admission dates did not overlap. The second instance involved the patients identified in Maryland and New Jersey. The patient identified in Maryland was a resident of New Jersey and had been hospitalized at the same time as the New Jersey patient, in the same New Jersey hospital, but on a different ward. This overlapping admission occurred approximately 6 months before C. auris was identified in the Maryland hospital.

“Specimens for surveillance cultures to evaluate patients for colonization were taken from the three living patients (one with C. auris in the blood, one in urine and one in the external ear canal),” the statement continues. “In all three cases, cultures yielded C. auris from at least one body site, including groin, axilla, nares, and rectum, 1–3 months after initial detection of C. auris. Environmental cultures of the hospital room were collected during a subsequent hospitalization of one of the Illinois patients who had a C. auris bloodstream infection 3 months earlier, and who remained persistently colonized in multiple body sites; samples taken from the mattress, bedside table, bed rail, chair, and windowsill all yielded C. auris. C. auris was not detected in this patient’s hospital room after terminal cleaning with sodium hypochlorite solution and ultraviolet light.”