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COVID-19: A New Door to Fungal Death

by , | Mar 23, 2026 | Mold and Health

When the coronavirus pandemic (COVID-19, caused by SARS-CoV-2) swept across the world in early 2020, most headlines focused on ventilators, vaccines, and how fast the virus was spreading.

But at the same time — quietly and often dangerously — another threat was growing inside many of the sickest patients:

Serious fungal infections that took hold while their bodies were already weakened.

Fungi are everywhere. Most of the time, a healthy immune system keeps them at bay.

But COVID-19 changed the rules.

The virus damaged lungs, depleted immune cells, and pushed millions of patients into intensive care units where powerful drugs further crushed their defenses.

The result was a surge in deadly fungal co-infections that many physicians and public health officials were not expecting.

This was not a small or rare problem. From January 2020 to December 2021, more than 13,000 U.S. residents died of fungal infections — a significant jump over pre-pandemic levels.

Nearly 22% of those deaths were directly associated with COVID-19.

For patients who developed a secondary fungal infection on top of their COVID-19 diagnosis, the risk of death was staggering.
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Understanding how COVID-19 opened the door to fungal illness is now one of the most urgent lessons of the pandemic — and a warning that applies far beyond the ICU.

Before COVID-19, fungal infections were already a global public health concern.

In 2024, researchers published updated estimates finding that fungal diseases cause approximately 6.5 million invasive infections and 3.8 million deaths per year worldwide.​

COVID-19 accelerated that already troubling trend dramatically. According to a landmark study published in Clinical Infectious Diseases, fungal hospitalization rates increased significantly during 2019–2021, and the increase was “primarily driven by hospitalizations of patients with COVID-19–associated fungal infections”.
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The death numbers within hospitals were devastating. COVID-19–associated fungal hospitalizations with the highest percentage of in-hospital deaths involved:

  • Aspergillosis: 57.6%
  • Invasive candidiasis: 55.4%
  • Mucormycosis: 44.7%
  • Unspecified mycoses: 59.0%

These patients were also far sicker overall. COVID-19–associated fungal infections were linked to a roughly fourfold increase in ICU admission rates and a twofold increase in in-hospital death rates compared to fungal infections in patients without COVID-19.
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The scale of this secondary crisis caught many hospitals by surprise.

COVID-19–Associated Pulmonary Aspergillosis, known as CAPA, became one of the most feared complications in ICUs worldwide.

A meta-analysis involving 1,437 COVID-19 ICU patients found a median ICU mortality rate of 56.8% among those who developed CAPA, ranging from 30% to 91.8% depending on the hospital and country.
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According to a 2024 study published in Clinical Infectious Diseases, “patients with CAPA had a 90-day mortality rate of 48% after ICU admission, significantly higher than the 21% observed in patients without CAPA”.
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Research from Science magazine explained a key biological reason for the risk: “While COVID-19 can send parts of the immune system into overdrive, it also depletes certain immune cells, leaving a patient less able to fight off other infections.

The extreme damage to cells lining the lung also impairs the organ’s ability to clear out respiratory pathogens like Aspergillus”.

The Fungal Players: Which Species Did the Most Damage

Three major groups of fungi emerged as COVID-19’s most dangerous co-infectors:
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Aspergillus

Aspergillus is a common mold found in soil, decomposing leaves, and indoor air. In healthy people, the immune system destroys its microscopic spores before they take hold. In COVID-19 patients — especially those on ventilators — the story was very different.

COVID-19–Associated Pulmonary Aspergillosis, known as CAPA, became one of the most feared complications in ICUs worldwide.

A meta-analysis involving 1,437 COVID-19 ICU patients found a median ICU mortality rate of 56.8% among those who developed CAPA, ranging from 30% to 91.8% depending on the hospital and country.
​
According to a 2024 study published in Clinical Infectious Diseases, “patients with CAPA had a 90-day mortality rate of 48% after ICU admission, significantly higher than the 21% observed in patients without CAPA”.​

Research from Science magazine explained a key biological reason for the risk: “While COVID-19 can send parts of the immune system into overdrive, it also depletes certain immune cells, leaving a patient less able to fight off other infections.

The extreme damage to cells lining the lung also impairs the organ’s ability to clear out respiratory pathogens like Aspergillus”.
​

Mucormycosis

Mucormycosis — caused by a group of molds called Mucorales — was particularly terrifying in the way it spread. It could invade the sinuses, orbit, and brain (rhino-orbital cerebral mucormycosis) or destroy the lungs.

Diabetes played an especially prominent role in mucormycosis cases.

Researchers documented that “if the patient is diabetic, the development of mucormycosis is most likely,” as “usage of corticosteroids can result in uncontrollable hyperglycemia” and “low pH supports the growth of mucormycosis”.

Blood sugar management in hospitalized COVID-19 patients was critically important — yet frequently difficult to achieve.

The condition gained international attention during India’s devastating second COVID-19 wave in 2021, where it reached near-epidemic proportions among diabetic patients treated with steroids.

A landmark systematic review published in The Lancet Microbe found that COVID-19–associated mucormycosis (CAM) carried an overall mortality rate of 49%, rising to 81% in patients with pulmonary or disseminated disease.
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A separate 2023 systematic review of 780 cases found the overall mortality rate was 38.9%, and confirmed that mucormycosis typically developed an average of 22 days after COVID-19 diagnosis. The review identified novel risk factors beyond traditional ones — including older age, Aspergillus co-infection, and use of the immune-suppressing drug tocilizumab.

Researchers also discovered that pulmonary mucormycosis combined with aspergillosis at the same time was particularly lethal.

A 2024 study found that patients with this “mixed mold infection” experienced early mortality at a rate of 42.9% versus 17.9% in patients with mucormycosis alone.
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Candida and Candida auris

Candida species — particularly the drug-resistant Candida auris — spread rapidly through COVID-19 hospital units.

Candida auris is a multidrug-resistant fungus that had been spreading slowly through healthcare facilities since it was first described in Japan in 2009.

COVID-19 turned a slow burn into a wildfire. Researchers in Israel documented a 30-fold increase in C. auris incidence in 2021 compared to prior years, directly corresponding with surges in COVID-19 hospitalizations.
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In New York City, Mount Sinai Hospital recorded that C. auris infection or colonization tripled during the COVID-19 pandemic. At another New York City hospital, incidence rates climbed from 2.6 cases per 10,000 admissions in 2019 to 7.8 per 10,000 in 2022 — a threefold increase.

The CDC investigated one striking outbreak in Florida in July 2020, where a COVID-19 specialty care unit experienced a cluster of C. auris bloodstream infections.

Investigators found that “HCP using multiple gown and glove layers in the COVID-19 unit, extended use of the underlayer of PPE, lapses in cleaning and disinfection of shared medical equipment, and lapses in adherence to hand hygiene likely contributed to widespread C. auris transmission”.
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Meanwhile, research from Weill Cornell Medicine showed that Candida albicans was flourishing not just in the lungs, but in the gut of severely ill COVID-19 patients.

As investigators reported: “Candida albicans increased in the intestines of patients during the course of severe COVID-19…

Severe and long COVID-19 were not thought to involve fungal blooms in the intestines that, in addition to the virus, can impact patient’s immunity*”*.

In preclinical models, mice exposed to gut fungi from COVID-19 patients showed more neutrophils in the blood and lungs and signs of heightened inflammation when infected with SARS-CoV-2 — but antifungal drugs reduced these effects.
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The Science: Why COVID-19 Makes Fungi Deadly

Understanding why COVID-19 unlocks fungal infections requires a look at what the virus does to the human body and the medical treatments patients receive.

COVID-19 does not simply cause illness — it disrupts the immune system in multiple, conflicting ways. On one hand, it can trigger a “cytokine storm,” an explosive over-reaction of the immune system that destroys healthy tissue.

On the other hand, SARS-CoV-2 directly depletes key immune cells, including CD4+ T cells and CD8+ T cells — the same cells responsible for fighting off opportunistic pathogens like fungi.
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According to a review published by Nature Microbiology, “Virus-infected cells release danger-associated molecular patterns (DAMPs)… to promote the release of proinflammatory cytokines and chemokines, and elicit the influx of macrophages and neutrophils, exacerbating the local inflammatory response”.

This chaotic immune environment simultaneously burns out the defenses that normally eliminate fungal spores.
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Structural damage to the lung lining also plays a key role. COVID-19 disrupts the epithelial cells lining the airways — the same barrier that traps and removes inhaled fungal spores before they can germinate.

The Corticosteroid Problem

The most critical drug in early COVID-19 treatment was dexamethasone — a powerful corticosteroid that was shown by the RECOVERY trial in 2020 to reduce COVID-19 deaths by up to one-third. It became the global standard of care. But it came with a dangerous trade-off.
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According to research published in a major critical care journal, invasive fungal infections were reported exclusively in dexamethasone-treated patients — 12% of those who received the drug versus 0% who did not (p<0.0001).

In the same study, dexamethasone-treated patients were over three times more likely to contract a superinfection, with an adjusted odds ratio of 3.7.
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The Alberta Health Services Scientific Advisory Group noted that “the clinician should remain vigilant towards the development of bacterial and fungal infections when dexamethasone or higher dosages of other corticosteroids are used”.
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Corticosteroids promote “functional impairments of several immune cells, including neutrophils and monocytes/macrophages, and also T cells,” according to the Nature Microbiology analysis.

Research commentary, PMC / NIH (2022) — “Defective Antifungal Immunity in Patients with COVID-19”:

“Prior to the administration of corticosteroids, the extensive damage to the respiratory epithelium due to the host immune response provides an environment suitable for secondary infection with Aspergillus… the administration of corticosteroids would boost infection through immune suppression, but possibly also enhancing further fungal growth.”

In other words, the very drug saving patients from the cytokine storm was simultaneously opening a window for fungi to invade.

Long COVID and Persistent Fungal Risk

The fungal threat did not end when the acute phase of COVID-19 resolved. Research increasingly suggests that disruption of fungal balance in the gut continues to affect patients long after discharge.

A 2023 study from Weill Cornell Medicine found that gut fungi — particularly Candida albicans — that bloomed during severe COVID-19 caused “long-lasting changes in the immune system.” The lead investigator noted:

“Severe and long COVID-19 were not thought to involve fungal blooms in the intestines that, in addition to the virus, can impact patient’s immunity”.
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Meanwhile, immunocompromised patients — transplant recipients, cancer patients, individuals with HIV — showed “increased fungal infection incidence, broader pathogen diversity, and more frequent exacerbations” in the post-COVID era.

Research confirmed that “post-COVID-19, transplant recipients exhibited increased fungal infection incidence,” reflecting “SARS-CoV-2-specific biological effects, such as immune dysregulation, endothelial damage and microbiome alterations”.
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Immunocompromised patients with persistent SARS-CoV-2 infection — defined as viral shedding beyond eight weeks — showed “increased mortality and invasive fungal infections”. The virus and the fungus were co-dependent threats.

Conclusion

The data are clear. A 6-fold increase in death risk for COVID-19 patients who developed fungal co-infections. A median ICU mortality of 56.8% for COVID-19–associated pulmonary aspergillosis. A 30-fold surge in drug-resistant Candida auris in some countries. More than 13,000 fungal deaths in the U.S. alone during 2020–2021, driven largely by the pandemic.

These numbers tell a story about how viral infections, immune dysfunction, life-saving drugs, and environmental fungi intersect in dangerous ways. They also tell a story about preparedness — about how healthcare systems that focus exclusively on the obvious threat may miss the secondary one growing alongside it.

For building professionals and indoor air quality experts, the lessons are equally clear: immunocompromised individuals are not just at risk in the hospital. A water-damaged home, a moldy basement, or a neglected HVAC system can be dangerous for anyone whose immune defenses have been compromised — by COVID-19, cancer treatment, or any other cause.

The fungi were here long before SARS-CoV-2. They will be here long after. COVID-19 simply showed us, in the most devastating way possible, what happens when we stop paying attention to them.

Let me finish by stating that antifungal treatment and its duration was a key predictor of survival of COVID-19.

Research confirmed that “longer antifungal treatment duration was linked to reduced mortality,” while elevated inflammation markers (CRP), palatal necrosis, and shorter antifungal therapy were independently associated with increased risk of death.

Now, let that sink in your brain to create a logical conclusion of how we are all going to get out of this fungal mess and modern plague.

References

Authors

  • Moe Bedard

    Moe is a certified mold inspector and remediator with 15+ years of experience, founder of Black Mold News, and CEO of Mold Safe Solutions—making him one of the most trusted names in the industry.

  • Chase Bedard is the Lead Science Researcher and Editor for Black Mold News and a graduate of the University of California, San Diego in cell biology. He is also a certified mold inspector and remediator with Mold Safe Solutions, combining scientific training with real-world field experience investigating mold and its health effects in homes and buildings.

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