Two people in the United States with normally functioning immune systems developed chronic lumps under the skin of their elbows, and the cause turned out to be a genus of fungus that ordinarily spends its life decaying dead wood.
The report appears in the September issue of the CDC journal Emerging Infectious Diseases, authored by G. S. Tansarli and colleagues. Both patients had chronic subcutaneous infection caused by Fomitiporella species, filamentous fungi in the phylum Basidiomycota. That is the group that shows up in the environment as gilled mushrooms and as the shelf or bracket fungi that grow off dead trunks and fallen logs, breaking the wood down. Almost none of them have any history of infecting people.
Both recovered after surgical excision, with no antifungal therapy at all.
A Genus That Was Not Known to Infect People Until Last Year
Fomitiporella is not a familiar name in clinical microbiology, and for good reason. Until recently, no species in the genus had been implicated in human disease.
That changed in August 2025, when clinicians at Albert Einstein College of Medicine and Montefiore Medical Center in the Bronx published the first known human case in Medical Mycology Case Reports. Their patient was a 69-year-old heart transplant recipient on immunosuppressants who had a skin nodule on his lower right leg. It was surgically removed, and DNA testing identified the organism as Fomitiporella micropora.
A noninvasive fungal workup had come back unhelpful: blood tests for galactomannan and beta-D-glucan, a urine Histoplasma antigen test, and a serum cryptococcal antigen test were all nondiagnostic. He received posaconazole for roughly two months, though the authors concluded that the excision was probably the curative step. The lesion has since healed completely.
Asked about exposures, he mentioned that he used to work in construction laying floor tiles, which put him on his knees.
The Test That Found It Skips the Culture Dish Entirely
Both the CDC report and the Bronx case turned on the same technology: broad-range fungal PCR run on formalin-fixed tissue, meaning the preserved biopsy block that pathology labs already store. In the Bronx case, the sample was sent to the University of Washington and amplified using primers targeting the internal transcribed spacer region and the 28S ribosomal RNA gene.
That matters because these fungi are hard to identify conventionally. Filamentous basidiomycetes often fail to produce spores in the laboratory, stripping away the microscopic features mycologists normally use to tell species apart. Under a microscope, they can look like generic clear-walled molds and be mistaken for far more dangerous organisms.
The CDC authors state the point plainly: the cases highlight the value of molecular diagnostics for detecting rare environmental fungi. Without sequencing, both sets of nodules would likely have been logged as fungal infection of unknown species.
A Growing List of Mushroom Relatives Turning Up in Patients
These are not isolated curiosities. In 2022, the same CDC journal reported two U.S. cases of Rigidoporus corticola infection, a white-rot fungus of plants that had not previously been established as a human pathogen. One patient, a 43-year-old man with chronic granulomatous disease and recurrent acute myeloid leukemia, developed invasive fungal sinusitis after chemotherapy. The other had a fungus ball inside a lung cavity. Both were immunocompromised. The authors closed by adding the organism to what they called the list of increasingly recognized filamentous basidiomycetes associated with human disease.
Hospital series are starting to catch up. A retrospective review from a Bangkok teaching hospital presented this year describes these environmental fungi as emerging opportunistic pathogens, particularly in people with weakened immunity. CDC maintains a running collection of fungal disease reports that has grown steadily over the past several years.
The recurring pattern in the subcutaneous cases is a slow, localized nodule after what was probably a minor skin injury, sitting for months before anyone investigates. None of the reported patients were doing anything exotic. The Bronx patient had spent years kneeling on floors laying tile.
What This Does and Does Not Mean for Readers
The practical scope is narrow. Two cases, however unusual, do not establish that a new fungal threat is spreading. Nothing in the CDC report suggests that people who garden, split firewood, or handle mulch face meaningful risk of Fomitiporella infection.
What the report changes is a diagnostic assumption. This particular genus had been seen in a human exactly once before, in a transplant recipient on immunosuppressants. Both patients in the CDC report were immunocompetent, which widens the population in whom clinicians might reasonably consider these organisms.
The treatment finding is equally notable and equally preliminary. Both cleared their infections with excision alone, which is consistent with the Bronx authors' assessment of their own case. But two patients do not make a guideline, and antifungal susceptibility data for Fomitiporella does not exist.
Anyone with a lump under the skin that has been slowly growing for months without pain, redness, or drainage should get it evaluated. Most such lesions have mundane explanations, and the point of this report is not that they are fungal. It is that when a biopsy shows fungus and the culture goes nowhere, sequencing can still produce an answer.
Key Questions Answered
What did the CDC report find?
Two immunocompetent patients in the United States developed chronic subcutaneous infections of the elbow caused by Fomitiporella species. Both recovered after surgical excision without antifungal therapy.
What is Fomitiporella?
A genus of filamentous basidiomycete fungi, relatives of mushrooms and bracket fungi, that normally decay wood. It was not reported as a human pathogen until 2025.
How was the infection identified?
Broad-range fungal PCR on formalin-fixed tissue. These fungi often fail to produce spores in culture, so conventional identification frequently fails.
Were the patients immunocompromised?
No. The CDC report specifies that both were immunocompetent, which is unusual for this class of infection.
Is this something the general public should worry about?
There is no evidence of a spreading threat. These cases remain extremely rare, and nothing in the report suggests routine outdoor exposure carries meaningful risk.
When should someone get a skin lump checked?
Any nodule that persists or slowly enlarges over weeks to months deserves evaluation, even without pain or drainage. Most have benign causes.
