A fungal superbug only recently reported in the U.S. has gotten a foothold, according to data published by the Centers for Disease Control and Prevention. Patients in frail health, especially those in hospitals and long-term care facilities, are especially vulnerable.

The number of U.S. patients infected with Candida auris had climbed to 200 clinical cases as of Dec. 31.

Patients can remain colonized with C. auris after an acute infection, and the fungus can persist on surfaces in healthcare environments. It can spread easily to patients in healthcare facilities.

In addition to clinical cases diagnosed by culture, an additional 285 U.S. patients were reportedly colonized with C. auris last year. The CDC screened patients in four states with clinical cases to help track the drug-resistant fungus.

In 2016, there were only seven cases nationwide. CDC officials warned healthcare facilities then to monitor for the fungus. It can cause serious medical complications when it enters the bloodstream through wounds, ventilators or catheters, Kaiser Health News reported.

Of the 200 clinical cases last year, 123 cases were reported in New York and another 48 occurred in New Jersey. California, Illinois and Florida also reported infections.

The fungus is commonly associated with hospital stays in certain countries, including India, Pakistan and South Africa.

Candida refers to a wide variety of microorganisms in the yeast family, such as those that cause athlete’s foot, oral thrush or yeast infections. C. auris, however, can attack organs and is difficult to treat.