A new study from the United States suggests that dangerous invasive mould infections may be more common than many experts once believed.
Although these infections are still considered uncommon, the research shows they can be life-threatening and deserve much greater attention from hospitals and public health officials.
The study was published by the U.S. Centers for Disease Control and Prevention (CDC). Researchers worked with four hospitals and their outpatient clinics in the Atlanta area to estimate how often these serious infections occur because doctors are not required to report them nationwide.
Mould is a type of fungus that grows naturally in the environment. It can also grow inside damp buildings after floods, storms, leaking roofs or plumbing problems. Most people breathe in mould spores every day without becoming sick because a healthy immune system removes them before they cause harm.
Problems begin when people have weakened immune systems. Older adults, cancer patients receiving chemotherapy, organ transplant recipients, and people taking medicines that suppress immunity are much more vulnerable. Some people who become seriously ill with COVID-19 also become more likely to develop invasive mould infections.
Unlike common mould allergies, invasive mould disease is much more serious. Instead of staying in the nose or airways, the fungus grows inside the body, often affecting the lungs before spreading to other organs. Without rapid treatment, the infection can become fatal.
Researchers reviewed medical records from 2020 to 2024. They first found almost 1,000 possible cases, but after carefully applying strict medical definitions, they confirmed about 450 patients truly had invasive mould disease.
The results were concerning. Around one-third of these patients died while they were still in hospital. Although many were already very ill because of other medical conditions, the findings show that invasive mould infections can make recovery much more difficult.
The researchers estimated that hospitals can expect roughly three to five cases each year for every 100 inpatient beds. Large teaching hospitals saw even more cases because they care for patients with complicated illnesses and severely weakened immune systems.
The study also raises questions about the future. Climate change is expected to increase flooding, hurricanes and other natural disasters that leave buildings damp for long periods. Damp conditions allow mould to grow rapidly, increasing opportunities for exposure. At the same time, ageing populations mean more people will have weaker immune systems, increasing the number of people at risk.
The researchers noted important limitations. The work involved only hospitals in one region of the United States, so infection rates could differ elsewhere because climate and environmental conditions vary. The study also could not determine exactly where patients first encountered the mould.
Even with these limitations, the research provides one of the clearest estimates yet of invasive mould disease in American hospitals. It gives hospital leaders a benchmark for recognising whether they are seeing expected numbers of cases or a possible outbreak.
This study is valuable because it fills a major gap in knowledge about a disease that has received relatively little attention. Its greatest strength is the careful review of patient records over five years using strict diagnostic criteria.
However, larger studies across different regions are still needed to confirm the findings and understand how climate, geography and hospital practices influence risk. If future research reaches similar conclusions, hospitals may need stronger surveillance systems and earlier screening for vulnerable patients.
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Source: U.S. Centers for Disease Control and Prevention (CDC).
