The first cases of a deadly, drug-resistant fungus identified in the United States may have contributed to the deaths of four patients, the Centers for Disease Control and Prevention reported on Friday.

The looming question is whether the fungus, Candida auris, will spread to long-term care. The fungus is often seen in hospitalized patients and is typically resistant to antifungal drugs. Thirteen cases of it have been identified in the U.S. so far, six of which were discovered recently and are still under investigation. The other seven cases were covered in the CDC’s Morbidity and Mortality Weekly Report.

The cases included in the CDC’s Friday report were identified in New York, Illinois, Maryland and New Jersey. All of the infected patients had underlying medical conditions, and had been in the hospital for an average of 18 days when the fungus was identified. Four of the hospitalized patients died, although it isn’t clear whether their deaths were caused by C. auris or underlying conditions.

In two of the cases, the patients had almost identical strains of the fungus, and had received treatment in the same location, a sign that the fungus could be spread in healthcare facilities, the CDC said.

“We need to act now to better understand, contain and stop the spread of this drug-resistant fungus,” said CDC Director Tom Frieden, M.D., M.P.H. “This is an emerging threat, and we need to protect vulnerable patients and others.”

The agency recommends that providers implement strict precautions to limit the spread of the fungus, and conduct thorough room cleaning with an EPA-registered disinfectant that works against fungi.