A fungus that barely registered on public health radars a decade ago has now been found spreading through hospitals and nursing homes in 23 states, with more than 3,000 clinical cases logged so far this year.

Candida auris, a yeast that can cause serious bloodstream infections in already sick patients, has proven unusually difficult to treat because it resists the drugs doctors normally reach for first. According to CDC surveillance data, more than 90% of C. auris samples tested are resistant to fluconazole, the antifungal most commonly prescribed for yeast infections, and roughly 40% resist two or more classes of antifungal drugs entirely. A small but growing number of cases have turned up resistant to every antifungal medication currently available.

Texas has reported the most cases of any state, with 706 as of mid-July, followed by Michigan with 503 and Illinois with 366. The fungus has now turned up in every major region of the country since it was first detected in the U.S. less than ten years ago, spreading largely through contact in healthcare settings rather than the general community.

The infections concentrate almost entirely among patients who are already seriously ill. People on ventilators, those with central venous catheters or urinary catheters, and residents of long-term acute care hospitals and skilled nursing facilities carry most of the risk. Healthy people without underlying medical conditions or recent hospital stays are rarely affected, and the fungus does not appear to spread easily outside of healthcare environments.

What worries infectious disease specialists is less the current case count and more the trajectory: cases have climbed steadily every year since C. auris first appeared in U.S. hospitals, tracking a broader global pattern of fungal infections growing harder to treat as resistance spreads. Hospitals in affected states have stepped up screening and isolation protocols for high-risk patients, though the CDC has not called for any changes to general public health guidance for people outside healthcare settings.