CDC Report: Detections of Deadly Brain Fungus Rose Fourfold at One U.S. Lab From 2023 to 2025

A rare mold that kills most people it infects is turning up more often in U.S. lab samples, and the country has no system to track it.

The CDC's Morbidity and Mortality Weekly Report, published Oct. 2, documents a roughly fourfold rise from 2023 to 2025 in detections of Cladophialophora bantiana. The data come from the clinical reference laboratory at the University of Washington, which tests specimens sent from around the country. The lead author is Joshua Lieberman of the University of Washington School of Medicine in Seattle.

The numbers

From January 2009 to July 2026, the lab identified 48 confirmed cases and one probable case. From 2009 through 2023, it found between one and five cases a year. It found eight in 2024 and 14 in 2025.

The rate rose too. From 2017 to 2023, the lab detected an average of 8.4 cases per 1,000 central nervous system specimens. In 2025 that was 26 per 1,000. The authors said the jump was not explained by an increase in lab referral volume alone.

The median patient age was 68. Cases came from 21 states and Washington, D.C. California reported six, Florida and Texas five each, and Pennsylvania four.

About 88% of the cases were found in brain tissue and 12% in lung samples. The authors wrote that the lung detections support the presumed respiratory route of infection. Direct entry through a skin injury is the other suspected route.

Why it matters clinically

The mold typically causes brain abscesses. The report puts the case-fatality rate at 60% to 70%, even with aggressive treatment.

Half of infected patients do not have weakened immune systems, according to the report. Lieberman told MedPage Today that this presents a concern because cases occur outside of those typical high-risk populations who have profound immunosuppression.

The authors urged clinicians to consider a fungal cause when a patient has signs of a brain abscess. Treatment calls for combination antifungal therapy and, when possible, surgical removal. The report says surgical excision might improve outcomes.

Diagnosis is hard. The report notes that PCR testing of spinal fluid came back negative in one case, even though tissue later showed the fungus. Lieberman said molds are difficult to grow in the lab.

What the data can and cannot show

The fourfold figure describes detections at one laboratory. It is not a national incidence rate.

Lieberman acknowledged that the rise could partly reflect more specimens being submitted and better molecular testing. The authors, though, said referral volume alone did not account for the change. Lieberman said at least one other U.S. specialized fungal lab has also seen more detections.

He also said the lab is probably undersampling, so the real incidence is likely higher than the count. "We think that that's probably going to be an underestimate of the true incidence," he said.

The report says why cases are rising is unknown and that more research into risk factors and potentially evolving virulence are warranted.

Lieberman offered climate as a leading hypothesis. "The other reasons that really jump to mind are a warming world and climate change," he told MedPage Today. He said evidence suggests some fungal pathogens are adapting to higher temperatures, and that human encroachment on the mold's environmental habitat could raise infection risk.

That is a hypothesis from the researcher, not a finding of the report. The authors wrote that the mold has only rarely been isolated from environmental sources. Many patients share no similar exposure history or risk factors.

The surveillance gap

National surveillance does not exist, and neither the environmental reservoir nor the route of infection is fully understood, the authors wrote.

So the best available count of this infection comes from a single university lab's testing archive, not a government reporting system. Nobody can say with confidence how many Americans have been infected, where they were exposed, or whether the trend is real or partly an artifact of better testing.

The CDC report calls for greater surveillance. Whether the agency or state health departments will set up reporting for the mold has not been announced. Until they do, UW's lab remains the main window into whether the 14 cases found in 2025 were a peak or the start of something larger.

The lab's 2026 count through July has not been published.