Are Brain Fungus Infections Really Increasing in the U.S.?

The evidence shows a real increase in detections of Cladophialophora bantiana at one U.S. reference laboratory. It does not establish that infections have increased across the country or explain why the laboratory saw more cases.

The October 2026 CDC report found that detections rose even after the University of Washington laboratory compared positive results with the number of central nervous system specimens it tested. That makes the signal important. But the United States has no routine national surveillance system for this fungus, so nobody can yet calculate a nationwide trend or a person’s chance of becoming infected from these data.

What the CDC numbers actually measure

The CDC report covers samples processed by one University of Washington clinical reference laboratory from January 2009 through July 1, 2026. It identified 48 confirmed infections and one probable infection. Forty-three detections came from brain or other intracranial CNS tissue; six came from lung samples.

The two rate comparisons are not interchangeable. The roughly 3.1-fold calculation compares 2025 with the 2017–2023 average: 26 divided by 8.4 is about 3.1. The CDC’s “approximately fourfold” figure compares 2025 with 2023 alone. Both are laboratory detection rates, not estimates of infections per person in the United States.

Dividing detections by submitted CNS specimens helps address one possible explanation: the laboratory may simply have tested more samples. The rate still increased. But this denominator cannot account for every change in which hospitals sent samples, which patients were tested, or what kinds of specimens were referred. The lab also changed its DNA extraction method in February 2021, although the report says the rest of the assay remained largely unchanged.

The CDC figure also shows earlier peaks in the adjusted rate, notably around 2013 and 2018. The recent level is higher, but the series has not climbed steadily year after year. With counts this small, a few cases can create a visible jump; the report does not provide an uncertainty estimate for the trend.

A laboratory signal is not a national trend

The reference lab received samples from 21 states and the District of Columbia. That shows the lab’s reach, not how many people in each state were infected. The sample is also shaped by clinical decisions: a patient must become ill, a clinician must suspect a fungal infection, a suitable specimen must be collected, and that specimen must be sent to this particular lab.

The CDC says routine national surveillance for C. bantiana does not exist. Without comparable data from other laboratories and a consistent way to identify cases, the 49 detections cannot show whether U.S. incidence rose, stayed flat, or changed unevenly across regions. They also cannot tell readers whether their personal risk has changed.

What other datasets add

A separate Meta-hosted case series searched a 4.95-million-patient electronic health record and reported 21 confirmed or probable cases: seven identified in brain samples and 14 in lung samples. The public summary says two of the seven brain-infection patients died. A Meta-hosted page summarizing contracted outside reviews includes a comment by clinical microbiologist Travis Price: the analysis did not identify a similar trend in cases, though different case-finding methods could explain the difference.

That is useful counterevidence, but it does not settle the question. The Meta cohort is small, comes from a different data system, and is not a national surveillance program. Meta’s public summary does not provide a comparable population rate. The underlying paper was not available for full methods inspection in the sources reviewed here, so the result should be read as a preliminary separate case series—not proof that the UW signal is false or that the national trend is flat.

A French retrospective study offers another point of comparison. Across 29 hospitals and French overseas territories, its national reference-center network identified 23 patients from 2002 through 2022. The annual count ranged from zero to two through 2021, then reached six in 2022. The authors noted that 2022 was France’s warmest year since 1900, but the study did not establish that warming caused the cases. It was a small retrospective series in a different country, not a measure of U.S. incidence.

Why detections might have risen

Several explanations remain possible, and the current evidence does not rank them confidently.

• A real increase in infections: The UW rate rose after adjustment for the number of specimens submitted. This supports a real change in that laboratory’s detection frequency, but a national change would need confirmation elsewhere.
• Changes in referrals or testing choices: More total CNS specimens alone do not explain the adjusted increase. Shifts in which hospitals send samples, which patients are selected for broad-range fungal testing, or how cases are recognized could still affect the rate.
• Environmental changes: The fungus’s abundance, range, or routes of exposure could change. The environmental reservoir is poorly understood, and the report did not collect enough exposure information to test this explanation.
• Changes in patients or diagnosis: Differences in the population being tested, clinical awareness, or diagnostic practices could produce more identifications without an equal change in underlying infection risk.
• Chance variation: The number of cases is small, and earlier adjusted-rate peaks show that the series fluctuated before the recent rise. More consistent data are needed to distinguish a sustained shift from short-term variation.
• A change in the organism: The CDC report raises evolving virulence as a research question. It presents no evidence that a new strain or genetic change caused the recent pattern.

Could climate change be responsible?

Climate change is a plausible general influence on fungal disease. The CDC’s climate guidance describes several possible pathways: fungi may survive in new places, extreme weather can move spores, and some fungi may adapt to warmer conditions. The CDC also says the effects on fungal disease remain poorly measured.

That general case does not establish a climate explanation for C. bantiana. This fungus already has substantial heat tolerance. A University of Toronto fungal collection record lists a strain received in 1960 as able to grow at 37°C and 42°C. A species-specific genomic study also describes growth at temperatures above normal body temperature. The collection’s 1960 date is when the strain was received, not a documented isolation date or proof of when its heat tolerance was first measured.

This evidence weakens one simple explanation: that the fungus only recently acquired the ability to survive at human body temperature. It does not rule out other climate-related effects, such as changes in where the fungus is found or how people encounter it. So far, the CDC data contain no exposure histories or environmental samples that link warming to the detections. The French study’s six cases in 2022 are a reason to ask more questions, not proof of cause.

The same distinction between a plausible mechanism and a demonstrated cause appears in Sherafy’s analysis of Frankfurt airport malaria. In both cases, a general environmental pathway can make a hypothesis worth investigating without showing that it caused a particular cluster.

What the disease’s severity does—and does not—mean

C. bantiana is a darkly pigmented mold that can cause a brain abscess, including in people without a recognized immune deficiency. Public-health assessments describe inhalation of airborne spores or direct inoculation through an injury as suspected routes; the fungus’s environmental reservoir remains uncertain. The reviewed sources do not document person-to-person spread.

The CDC cites a historical case-fatality estimate of about 60%–70% among diagnosed infections. A 2017 systematic review of published cerebral cases reported mortality of 65%. These figures describe outcomes among people already diagnosed with a severe infection. They do not mean that a person has a 60%–70% chance of getting the disease, and they do not measure the risk faced by the general public.

The 2026 UW series cannot calculate its own case-fatality rate. The report describes one fatal patient treated at UW Medical Center; outcome information for the other cases was unavailable. The small Meta series, with two deaths among seven brain cases, is also too small and differently ascertained to replace historical estimates.

Diagnosis can be difficult because symptoms and scans may resemble other brain abscesses or tumors. A historical review of 124 culture-proven brain cases reported an average of 115 days from symptoms to diagnosis; that is an older literature-based estimate, not a current expected delay. In the CDC report, cerebrospinal-fluid molecular tests were negative in the one fatal UW case, including a sample collected a month before a brain biopsy. That example shows why a negative spinal-fluid result cannot by itself rule out every brain infection.

The best treatment is not established. In the small French study, survival appeared higher among patients who received at least two weeks of triple antifungal therapy, but treatment was not randomly assigned and the groups were small. The apparent difference for surgery was also based on only 15 patients and was not statistically significant. These findings can guide specialist discussion; they do not establish a guaranteed regimen or a two-week cure.

A headache by itself cannot identify this rare fungus. The CDC report calls on clinicians to consider C. bantiana in patients with signs of a brain abscess and calls for more systematic case reporting. The UW data provide no population-level estimate of personal risk.

What the CDC is investigating next

On October 13, the California Department of Public Health posted a laboratory bulletin saying the CDC was seeking help identifying C. bantiana infections from January 1, 2020 onward, with epidemiologic and clinical follow-up. That effort may help find cases outside the UW laboratory. It is an active case-identification effort, not yet a routine nationwide reporting system.

To determine whether infections are increasing nationally, investigators would need comparable case counts from multiple laboratories, consistent definitions of confirmed and probable infections, and denominators showing how many comparable specimens were tested. They would also need information about referral patterns, assay changes, patient characteristics, geography, and possible exposures. Environmental or genetic evidence could help evaluate specific explanations, including climate effects.

For now, the strongest conclusion is narrow but consequential: one laboratory has seen more C. bantiana detections even after adjusting for the number of CNS specimens it tested. Scientists have not yet shown whether infections are increasing across the United States or what caused the laboratory signal.

References and Further Reading

Primary public-health records and data

• CDC MMWR: Molecular Detections of Cladophialophora bantiana at a Clinical Reference Laboratory — United States, 2009–2026 — The original case series, testing-volume adjustment, annual counts, limitations, and figure.
• California Department of Public Health: Cladophialophora bantiana Case Identification — The October 13 bulletin describing CDC’s request for retrospective case identification and follow-up.
• CDC: Climate Change and Fungal Diseases — General pathways through which climate and weather may affect fungi, alongside CDC’s stated evidence gaps.
• Public Health Agency of Canada: Cladophialophora bantiana Pathogen Safety Data Sheet — Background on suspected exposure routes, the uncertain environmental reservoir, and diagnostic methods.

Independent datasets and clinical research

• Meta AI Research: Cladophialophora bantiana: a US Clinical Case Series Assisted by Artificial Intelligence — A separate EHR case series. Meta’s broader research post also publishes outside-review comments about its trend comparison and limitations.
• Meta AI Research: Accelerating Scientific Research in Health Data Science With Muse Models — Meta’s account of the research process and contracted outside-review summaries, including comments on the C. bantiana case series.
• Lortholary et al., French Retrospective Nation-Based Study — A 23-patient study covering France and overseas territories from 2002 through 2022, including the 2022 cluster and small treatment comparisons.
• Kantarcioglu et al., Systematic Review of Cerebral C. bantiana Cases — Historical clinical cases underlying the high case-fatality estimates; these are not population-risk estimates.
• Chakrabarti et al., Review of 124 C. bantiana Brain Abscess Cases — Historical review reporting diagnostic delays and outcomes in published cases.
• UAMH Centre for Fungal Biodiversity: Strain UAMH 813 — Collection record listing a strain received in 1960 and its recorded growth at 37°C and 42°C.
• Chen et al., Genomic Analysis of C. bantiana — Species-specific genomic research describing thermotolerance; it does not test the cause of the 2026 U.S. detection signal.
• Case Report: Fatal Cerebral Phaeohyphomycosis Mimicking a Tuberculous Brain Abscess — An illustrative clinical report on diagnostic overlap and the need for tissue-based identification.
• Hoenigl et al., Global Guideline for Rare Mould Infections — International specialist guidance covering rare mould diagnosis and management, with acknowledged evidence constraints.

Currency note: Research checked through October 23, 2026. The CDC laboratory series stops on July 1, 2026, and the case-identification request is ongoing. Reassess if CDC publishes multi-laboratory results or a national surveillance method.