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A CDC-published report describes a sharp rise in detections of Cladophialophora bantiana, a rare fungus that can cause brain abscesses. One U.S. reference laboratory recorded 14 cases in 2025, up from an annual range of one to five during 2009–2023; researchers say the increase’s cause and the infection’s true incidence are unknown.
A CDC-published report describes an increase in detections of Cladophialophora bantiana, a rare fungus that commonly causes brain abscesses and can be fatal. A University of Washington clinical reference laboratory identified 14 cases in 2025, compared with one to five per year from 2009 through 2023; researchers say it is not clear whether the rise reflects more infections or changes in testing and detection.
The laboratory identified 48 confirmed cases and one probable case between January 2009 and July 2026. Annual detections rose to eight in 2024 and 14 in 2025. The report, by University of Washington researchers, was published in the CDC’s Morbidity and Mortality Weekly Report. These are findings from a laboratory that tests samples from across the country, not a complete national count.
Intracranial central nervous system tissue accounted for 88% of the specimens in which the fungus was detected; lung specimens accounted for 12%. The researchers said the lung findings are consistent with a presumed respiratory route of infection. Cases were identified in samples from 21 states and Washington, D.C. California had six detections, Florida and Texas had five each, and Pennsylvania had four. The median age among the 49 patients was 68.
The researchers reported that the detected case rate rose from an annual average of 8.4 cases per 1,000 CNS specimens in 2017–2023 to 26 per 1,000 in 2025. This is a rate among specimens processed by the laboratory, not an estimate of the infection rate in the U.S. population. The report says C. bantiana infections can carry a case-fatality rate of up to 70%; that figure describes reported risk, not the outcome for every patient.
Why Brain Infections Are Difficult to Detect
The findings matter because C. bantiana can cause severe brain abscesses and has been found in people who do not appear to have major immune-system problems. That can make the infection harder to anticipate, especially when a brain abscess has no clear cause. The report does not establish that cases are increasing nationwide, but it gives clinicians and laboratories a reason to keep the fungus in mind when routine tests do not identify a cause.
Diagnosis can be difficult: the researchers said molds may not grow readily in laboratory cultures, and they believe cases are likely undercounted. The report’s sample-based rate also shows that the number of detections depends partly on which specimens are submitted and what tests are used. Those limits make it difficult to tell how much the observed rise reflects changes in disease occurrence rather than changes in recognition.
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What the Laboratory Data Show
Cladophialophora bantiana is a mold associated with brain abscesses and other central nervous system infections. The researchers described inhalation or direct inoculation after a skin injury as presumed ways the fungus may enter the body. Why it appears to affect the brain so often remains uncertain.
Joshua Lieberman, a University of Washington researcher and co-author, told MedPage Today that the laboratory’s annual detections stayed between one and five from 2009 through 2023 before rising in 2024 and 2025. He said at least one other specialized fungal laboratory in the U.S. had also seen an increase. The report’s figures nevertheless come from a limited number of laboratories and do not establish the national trend.
Lieberman said possible explanations include more specimens being submitted, improved detection through molecular testing, environmental changes associated with a warming climate, or greater human contact with environmental sources of the fungus. These were possibilities raised by the researcher, not causes demonstrated by the report.
“C. bantiana is a rare but important cause of brain abscess in both healthy and immunosuppressed people.”
— Joshua Lieberman, University of Washington School of Medicine researcher, speaking to MedPage Today
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Why the Case Increase Is Unclear
The cause of the rise is not established. More specimens, better molecular testing, environmental factors, or other changes could contribute, but the laboratory data cannot determine which explanation is correct. Nor do 49 confirmed and probable detections establish how many people in the country have been infected.
The findings cover samples submitted to one reference laboratory, and the report does not provide a population-based incidence estimate. Although Lieberman told MedPage Today that another specialized U.S. laboratory had seen a rise, the material does not give comparable counts from that laboratory. It also remains unclear how often infections are missed or how the reported fatality risk applies across different patients and treatment circumstances.
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What Clinicians and Researchers May Track
Clinicians evaluating a brain abscess with no diagnosis from routine cultures or cerebrospinal fluid testing may consider rare causes such as C. bantiana, particularly when a patient appears otherwise healthy, Lieberman suggested. The report also describes treatment as involving surgical removal of the abscess along with combination antifungal therapy; treatment decisions belong to the patient’s medical team.
Further data from laboratories and public health reporting would help show whether detections continue to rise and whether the trend is seen more broadly. Researchers would also need better information on testing volume, diagnostic methods, and possible exposures to distinguish a true increase in infections from changes in detection. The current report does not announce a new national surveillance program or identify a confirmed source of exposure.
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Key Questions
What is Cladophialophora bantiana?
C. bantiana is a mold that can cause serious infections, most often involving the central nervous system and presenting as a brain abscess.
How many cases did the report identify?
A University of Washington reference laboratory identified 48 confirmed and one probable case from January 2009 through July 2026. The total is not a complete count of U.S. infections.
Does the report prove infections are increasing nationwide?
No. It documents increased detections at one laboratory, including 14 cases in 2025. The report does not establish a nationwide trend or a population-based infection rate.
What may explain the increase in detections?
The cause is unknown. Researchers raised possibilities including more submitted samples, improved molecular testing, environmental changes, and increased human contact with environmental sources; none is established by the report.
Who can be affected by the infection?
The report describes infections in both immunosuppressed people and people who appeared otherwise healthy. Anyone with health concerns should seek advice from a qualified medical professional.
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