Deadly mold: First-of-its-kind study reveals the dimensions of the hidden danger

A new study by the U.S. Centers for Disease Control and Prevention (CDC) indicates that invasive mold infections may be a much more serious threat than previously estimated. The findings, reported this week in the agency's official weekly publication (MMWR), represent an attempt to estimate for the first time, and systematically, how common the disease actually is.

"This is almost the first time we have such an estimate," said Dr. Jeremy Gold of the CDC, the senior researcher who led the study. The reason: invasive mold-type fungal infection is not a disease that doctors in the U.S. are required to report to health authorities, and therefore its true scope has remained unknown at the national level until now.

What is mold, and how does it become dangerous?

Mold is a type of fungus that develops in nature as a thin network of microscopic threads. It is very common both in the external environment and inside buildings, and is usually not dangerous to people with a normal immune system. The problem begins when the mold releases tiny, invisible spores into the air. For most people, inhaling mold spores does not cause illness at all - the immune system simply deals with them.

But for people with a weakened immune system - such as cancer patients, organ transplant recipients, or those taking immunosuppressive drugs - the spores can "take hold" in body tissues and cause what is called an "invasive fungal infection": a condition where the fungus actually penetrates tissues and damages them, as opposed to casual exposure that does not cause harm.

It is important to clarify: not every invasive fungal infection is of the mold type - there are also non-mold fungi, such as Candida-type yeasts, that cause other types of fungal infections. The current study focused specifically on infections caused by mold species. The infection can affect the lungs (the most affected organ), sinuses, skin, central nervous system, or several organs simultaneously. In addition to inhalation, mold can enter the body through open wounds or cuts, and sometimes even through contaminated medical equipment in hospitals.

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High mortality rate

For the study, the team tracked laboratory test results at four hospitals in the Atlanta area between 2020 and 2024. Initially, 968 patients with suspected invasive fungal infection were identified. After careful examination according to strict medical criteria, 449 cases were confirmed - about 46% of the patients examined.

Of the 449 diagnosed cases, about 13% were patients who were also diagnosed with COVID-19. Most patients (43%) were aged 45 to 64, and another 39% were over 65. Children accounted for less than one percent of the disease cases. The lungs were the organ most affected (68% of cases), followed by infections of the skin and deep tissues, sinuses and nose, and the central nervous system.

The mortality rate from all causes within 90 days of diagnosis was 45%. The study found that results were particularly severe among patients who were also diagnosed with COVID-19: their intensive care hospitalization rate reached 66%, compared to 39% among infection patients without COVID-19, and their 90-day mortality rate was 66%, compared to 41% among those not diagnosed with COVID-19.

Another finding that the researchers emphasize: about 35% of the patients did not carry any of the "classic" known risk factors for the disease. The implication, according to the researchers, is that medical monitoring based only on known risk populations may miss a significant portion of actual patients.

"Frequency of infections will rise"

According to Dr. Gold, it is important to understand the scope of the problem now, because it may worsen in the future: mold exposure is a recurring problem following hurricanes, floods, and other natural disasters influenced by climate change. "I agree that the frequency of fungal infections is expected to rise with climate change," said Dr. Jeffrey Jenks, an infectious disease researcher at Duke University.