The Centers for Disease Control and Prevention (CDC) has reported cases of people contracting a potentially deadly fungal infection from Candida auris that is resistant to all antifungal drugs.

The five cases, reported in Washington, D.C. and Texas, occurred in long-term care facilities, which includes nursing homes and hospitals where many have weakened immune systems, putting them at greater risk.

Fungi have previously been found resistant to treatment by the three classes of antifungals —azoles, polyenes, and echinocandins — but this marks the first time in the U.S. that a strain has been found to be “pan-resistant,” the CDC said.