Cases of deadly brain mold rise sharply

The number of confirmed cases of a rare and deadly brain infection caused by Cladophialophora bantiana has quadrupled in the United States over the past two years. A report published in the Morbidity and Mortality Weekly Report by researchers from the University of Washington and the Centers for Disease Control and Prevention found that the increase in cases has occurred even though few laboratories are equipped to detect the fungus.

Surveillance reveals growing trend

The University of Washington laboratory, which collects samples from across the country, confirmed 48 cases and one probable case from 21 states between January 2009 and July 2026. The annual rate of infection was very low for fifteen years, averaging about five cases per year until 2023, after which it rose to eight in 2024 and fourteen in 2025. The frequency of the fungus in brain samples also increased significantly during this period.

Mystery of infection and patient profile

Researchers believe the increase in cases is real and not just due to more testing. Doctors do not yet understand how the fungus reaches the brain, though experts suspect it enters through the lungs or through a wound and then travels to the brain via the bloodstream. In the American cases, 12 percent of the positive samples came from lung tissue, suggesting a respiratory pathway. However, this does not fully explain the patient profile, as nearly half of those infected had no known immunosuppression, which is typically a risk factor for severe fungal infections.

Challenges in diagnosis and treatment

The fungus, Cladophialophora bantiana, has a long medical history, with the first recorded description dating back to 1911. It contains melanin, a dark pigment that helps it evade the immune system. Despite this, no national surveillance system in the United States tracks these infections, making it difficult to estimate how many people are affected each year. Early diagnosis is crucial, as treatment with antifungal drugs is most effective when started quickly. However, the infection is still fatal in 60 to 70 percent of cases.

Ongoing research and diagnostic challenges

The Seattle laboratory continues to detect the fungus, with 2025 marking the highest number of cases since 2009. A molecular test can now identify the fungus in tissue samples, but it must be specifically requested. In one case, two tests on cerebrospinal fluid returned negative results before a biopsy confirmed the infection, highlighting the challenges in diagnosing this rare condition.