A rare and deadly fungal infection capable of attacking the human brain is being detected at increasing rates across the United States, prompting federal health officials to issue warnings. The Centers for Disease Control and Prevention (CDC) has identified a concerning rise in cases involving Cladophialophora bantiana, a darkly pigmented, yeast-like mold known to cause severe infections.
"Reasons for the apparent increase are unknown." CDC report
According to a new CDC report, laboratory detections of C. bantiana nearly quadrupled between 2023 and 2025. This surge raises significant concerns about a pathogen that carries a high mortality rate and can affect individuals with otherwise healthy immune systems, setting it apart from many fungal infections that primarily threaten those with weakened immunity.
Researchers from the University of Washington analyzed tissue samples collected between January 2009 and July 2026. Their study identified 48 confirmed infections and one probable case across 21 states and Washington, D.C., highlighting the broad geographic distribution of the fungus. The median age of affected patients was 68 years. Notably, approximately half of C. bantiana infections have been observed in individuals without any diagnosed underlying immune deficiencies, underscoring its unique threat profile.
The fungus is believed to enter the body through inhalation or an open wound before potentially traveling through the bloodstream to the brain. Once it reaches the brain, the infection can produce dangerous abscesses, which are notoriously difficult to diagnose and treat effectively. The University of Washington researchers found that 88% of the identified infections involved brain tissue, while the remaining 12% were detected in lung tissue.
The condition carries a particularly alarming mortality rate. A systematic review published in the medical journal *Medical Mycology* indicates that between 60% and 70% of patients with the infection die, even when aggressive medical treatment, including surgical removal of infected tissue and multiple antifungal medications, is provided. This high fatality rate, combined with the fungus's ability to infect healthy individuals, has intensified federal researchers' efforts to understand the recent increase in detections.
Between 2009 and 2023, the University of Washington microbiology laboratory, a key diagnostic center, typically identified only one to five cases annually. However, this figure climbed significantly to eight cases in 2024 before reaching 14 in 2025. To ascertain whether this increase simply reflected more extensive testing, researchers compared positive detections against the total number of brain tissue specimens examined for fungal infections. The analysis revealed a clear rise in detection rates, climbing from 8.4 cases per 1,000 specimens between 2017 and 2023 to 26 cases per 1,000 specimens in 2025.
Despite these findings, the specific reasons for the apparent increase remain elusive. "Reasons for the apparent increase are unknown," the CDC report stated, indicating that officials have not yet identified what is driving the elevated laboratory detections.
The findings also revealed a widespread distribution of infections. California recorded the highest number of cases with six, followed by Florida and Texas with five each. Pennsylvania reported four cases.
Health officials are particularly concerned about the challenges involved in identifying the infection before substantial and irreversible damage occurs. C. bantiana can develop into a brain abscess without producing obvious external symptoms, making early detection exceedingly difficult. In one fatal case documented at the University of Washington Medical Center, spinal fluid tests returned negative results despite the confirmed presence of the fungus. These negative findings occurred both a month before and at the time of a brain biopsy, demonstrating how conventional testing methods can fail to identify the infection. Consequently, physicians may need to obtain tissue samples through surgical procedures to establish a definitive diagnosis.
In response to the growing concern, the CDC is urging medical professionals across the country to consider rare fungal pathogens, including C. bantiana, when evaluating patients with suspected brain abscesses. Additionally, researchers are calling for systematic nationwide reporting to improve surveillance and more accurately determine whether these infections are becoming more common across the country. While the infection remains rare, its high fatality rate and ability to impact otherwise healthy individuals have elevated its profile among researchers and public health officials investigating its apparent spread.
