SEATTLE
It doesn't care if you're young and fit. It doesn't need you to be sick first. And once it reaches your brain, it kills somewhere between six and seven out of every ten people it infects, even when doctors throw everything they have at it.
Its name is Cladophialophora bantiana, a dark, slow-growing mold that most doctors will never see in their entire careers. But a new report from the US Centers for Disease Control and Prevention (CDC) says that this rare killer is turning up far more often than it used to, and nobody can explain why.
Scientists at the University of Washington in Seattle, working with a CDC fungal disease expert, found that detections of the brain-invading mold at their national testing laboratory jumped roughly fourfold between 2023 and 2025. In 2025 alone they confirmed 14 cases, compared with between one and five cases a year for well over a decade before.
"Reasons for the apparent increase are unknown," the researchers wrote bluntly in the CDC's Morbidity and Mortality Weekly Report, published on October 2. Since then the story has spread through medical news sites and science outlets, with headlines warning of a "deadly mold that attacks the brain."
So should you be worried? The short answer is: not panicked, but paying attention. Here's what we know, what we don't, and why doctors are being told to keep this obscure fungus on their radar.
A killer hiding in plain sight
Most fungal infections that reach the brain are opportunists. They prey on people whose immune systems are already battered by cancer treatment, organ transplants, uncontrolled HIV or powerful immune-suppressing drugs. They typically start somewhere else in the body, such as the lungs or the sinuses, and spread to the brain only later.
C. bantiana breaks those rules. It belongs to a group of so-called "black molds" (scientists call them dematiaceous fungi) that carry melanin, the same pigment that colours human skin, in their cell walls. And once it is inside the body, it seems to head straight for the brain, where it forms abscesses: swollen pockets of pus, fungus and dead tissue that press on the surrounding brain.
Even more alarming, it does not need a weakened host. According to the CDC report, roughly half of the people who develop C. bantiana infections have no prior condition weakening their immune system.
"It is capable of infecting apparently healthy people, not just immunocompromised patients in whom we normally worry about invasive fungal disease," Dr Joshua Lieberman, a microbiologist and associate professor of laboratory medicine and pathology at the University of Washington and the report's senior author, told the science site Gizmodo.
The death rate is grim. Medical literature puts the case-fatality rate at 60% to 70%, even with aggressive treatment.
The numbers behind the alarm
The new findings come from a single but unusually well-placed laboratory. The University of Washington runs a specialist molecular microbiology reference lab that hospitals across the country send tissue samples to when they suspect a fungal infection but can't identify it. The lab uses a technique called broad-range fungal PCR, which reads the DNA of whatever fungus is in a sample and identifies it.
The team went back through every C. bantiana detection from January 2009 to July 2026. They found:
Crucially, the researchers checked whether the jump could simply be explained by more hospitals sending more samples. It couldn't. Between 2017 and 2023, the lab found an average of 8.4 C. bantiana cases for every 1,000 brain and spinal samples it tested for fungi. By 2025, that rate had climbed to 26 per 1,000, an increase of about 210%.
"We tried to control for increased testing as an explanation. Even though we tested more samples from the central nervous system over time, the number of C. bantiana cases increased faster. So we think the increase is real," Lieberman told Gizmodo.
"We don't know where it lives"
Here is the part that should make public health officials uneasy: scientists know remarkably little about this fungus, even though it was first described more than a century ago, in 1911, from a brain abscess.
They don't know its natural home. C. bantiana has only rarely been found in soil, rotting wood or anywhere else in the environment. They are not fully sure how people catch it. The leading theory is that spores are breathed in, or enter through a cut or scrape on the skin, before travelling through the bloodstream to the brain. The new data back the breathing theory slightly: finding the fungus in lung samples in 12% of cases suggests the lungs are at least one way in.
They also don't know why it prefers the brain, why it can infect healthy people, or why it seems to be on the rise.
"We need to understand where and how people are exposed. We think this is in the environment and people breathe in spores, but we don't know enough about where it occurs naturally," Lieberman said.
And many patients don't share any obvious exposure. There is no common job, hobby or location that links them.
Nobody is counting
Perhaps the most worrying detail in the CDC report is not a number at all. It is the absence of one.
There is no national surveillance system for C. bantiana. Doctors are not required to report cases to their local or state health departments. That means the University of Washington's figures, while striking, are only the cases that happened to be sent to one laboratory. Other hospitals test samples in-house or use other reference labs. Many brain abscesses are never tested for this particular mold at all.
The report's authors also had limited information about the patients behind each sample. Because a reference lab only receives tissue, they often didn't know what the patients did for a living, whether they were immunocompromised, or whether they survived. Outcome information was available for just one case, a patient treated at the University of Washington's own medical centre, who died. In that case, tests of the patient's spinal fluid, taken at the same time as a brain biopsy and a month earlier, came back negative for the fungus, showing how hard it can be to catch without operating.
"We need systematic data collection from clinical laboratories across the US to understand how many cases there really are. Although we think cases are still rare, we don't have a clear picture of the disease burden right now," Lieberman told Gizmodo.
The CDC report calls for exactly that: systematic reporting of C. bantiana cases, and for clinical labs to publish how many they detect.
Expert perspective: rare, serious, and worth watching
It is important to keep this in proportion. Fourteen confirmed cases in a year, in a country of more than 340 million people, is still a tiny number. Even if the true total is several times higher, your personal chance of encountering this fungus remains extremely small.
But infectious disease specialists pay attention to rare pathogens that are rising, because "rare" is the stage at which you have the best chance of understanding a threat before it grows. And fungi in particular have been surprising scientists lately. Drug-resistant Candida auris has spread through US hospitals and nursing homes over the past decade. Researchers are tracking the spread of a hard-to-treat ringworm fungus around the world. Fungal diseases once confined to particular regions, such as Valley fever in the US Southwest, have been turning up in new places.
The CDC report doesn't speculate about whether climate change, building work that disturbs soil, changes in the fungus itself, or better detection might be behind the C. bantiana increase. The authors specifically say that "further research into epidemiologic risk factors and potentially evolving virulence" (meaning the possibility that the fungus is becoming more aggressive) "are warranted."
For doctors, the message is practical. The report urges clinicians to "consider C. bantiana in patients who have signs and symptoms of a brain abscess," and to order molecular fungal testing on tissue or spinal fluid through a reference laboratory.
Speed matters. Patients with infection "require prompt antifungal therapy," the authors write, and "surgical excision might improve patient outcomes." They point to a 2024 French study of 23 patients in which surgically removing or draining the brain abscess was linked to better results. No one knows the single best drug regimen, but a combination of three antifungals (liposomal amphotericin B, either posaconazole or voriconazole, and flucytosine), given for at least two weeks, has shown some effectiveness.
What this means for you
First, the reassuring part. This is not a contagious disease. There is no evidence that C. bantiana passes from person to person. There is no outbreak in a single town or hospital. And the overwhelming majority of people will never be exposed to it in a way that makes them ill.
Still, a few common-sense points are worth knowing.
Know the warning signs of a brain abscess. Whatever the cause (bacteria are far more common culprits than fungi), a brain abscess is a medical emergency. Symptoms can include:
If you or someone you love develops these, especially a worsening headache with any neurological change, seek emergency care. Don't wait it out.
Look after cuts and scrapes. Because skin wounds are one possible entry route for many environmental fungi, clean cuts promptly, especially those picked up while gardening, doing yard work or handling soil and wood, and get medical advice for wounds that become red, swollen or won't heal.
Protect your lungs during dusty work. Wearing a well-fitted mask such as an N95 when clearing heavy dust, mouldy debris or soil in enclosed spaces is a sensible habit for many reasons, and it reduces exposure to fungal spores of all kinds.
Ask questions if a diagnosis is unclear. If a family member is being treated for a brain abscess that isn't responding to antibiotics, it is reasonable to ask the medical team whether fungal causes have been tested for. The CDC report is, in part, a reminder to doctors that this possibility exists.
Don't fall for scare marketing. Expect to see "anti-mold" supplements, air purifiers and home testing kits promoted off the back of these headlines. There is no evidence that any such product protects against C. bantiana, whose environmental hiding place hasn't even been identified.
The bottom line
The story of C. bantiana is, above all, a story about blind spots. A fungus that can kill healthy adults, that seems to be appearing more often, and that hides somewhere in our environment, is being tracked by what amounts to one laboratory's records and a scattering of case reports.
The risk to any one person remains very low. But the scientists who sounded this alarm aren't asking the public to panic. They are asking the medical system to start counting. Until labs and health departments begin systematically recording every case, the most honest answer to "how big is this problem?" is the one the researchers themselves give: we don't know yet.
And when it comes to a mold that kills most of the people it reaches, "we don't know" is a reason to find out fast.
