Fungal pneumonia is a lung infection caused by inhaling fungal spores that settle into the air sacs and trigger inflammation. Unlike bacterial or viral pneumonia, which are far more common, fungal pneumonia tends to strike people with weakened immune systems and can be difficult to diagnose because its symptoms overlap with other respiratory infections. It ranges from mild and self-resolving to life-threatening, depending on the type of fungus and the person’s immune status.
How Fungal Pneumonia Develops
Fungi release microscopic spores into the air, often from soil, decaying matter, bird droppings, or construction dust. When you breathe these spores in, they travel deep into the lungs and reach the tiny air sacs where oxygen exchange happens. In a healthy person, immune cells rapidly detect and destroy these spores before they can take hold. But when the immune system is compromised, the fungi can colonize lung tissue, multiply, and cause the air sacs to fill with fluid or pus.
This is what separates fungal pneumonia from the bacterial and viral types most people are familiar with. Bacterial pneumonia often develops quickly after a cold or flu, caused by common bacteria that are already present in the nose or throat. Fungal pneumonia, by contrast, typically requires either a specific environmental exposure or a gap in immune defense. It also tends to develop more slowly, sometimes over weeks rather than days.
The Fungi That Cause It
Fungal pneumonia falls into two broad categories: opportunistic infections that exploit a weakened immune system, and endemic infections tied to specific geographic regions.
Opportunistic Fungi
The most significant opportunistic lung pathogens are Aspergillus and Cryptococcus. Aspergillus spores are everywhere, in soil, air vents, compost, even hospital environments. Most people inhale them regularly without consequence, but in someone with a compromised immune system, they can cause invasive pulmonary aspergillosis, a serious and potentially fatal infection. Cryptococcus is commonly found in soil contaminated with bird droppings and is a particular threat to people with HIV/AIDS. Pneumocystis, another opportunistic fungus, causes a distinct form of pneumonia that was one of the earliest recognized complications of AIDS.
Endemic Fungi
Some fungi live in the soil of specific regions and can cause pneumonia even in otherwise healthy people who inhale a large enough dose of spores. In the United States, the three main endemic species are Histoplasma, Coccidioides, and Blastomyces. Histoplasma is found on every continent except Antarctica and is concentrated in the Ohio and Mississippi River valleys, where it thrives in soil enriched by bat and bird droppings. Coccidioides lives in the dry soils of the southwestern U.S., Mexico, and parts of Central and South America, causing what’s commonly known as Valley fever. Blastomyces is found in the Great Lakes region, the Ohio and Mississippi River valleys, and parts of Africa and Asia.
These fungi are increasingly being diagnosed outside their traditional geographic zones, so living in a “non-endemic” area doesn’t rule out infection entirely.
Who Is Most at Risk
A weakened immune system is the single biggest risk factor. The CDC identifies several groups at elevated risk:
- People with HIV/AIDS, especially those with very low white blood cell counts
- Organ transplant recipients, who take medications that deliberately suppress the immune system to prevent organ rejection. Lung, liver, heart, and small bowel transplants carry particularly high risk.
- Stem cell transplant recipients, whose immune systems are destroyed and rebuilt during the process
- Cancer patients on chemotherapy or radiation, which lower white blood cell counts
- People with chronic lung disease, whose lungs are already damaged and more vulnerable to colonization
- People on long-term corticosteroids or high-dose antibiotics, both of which can suppress immune defenses
Long hospital stays also increase risk, partly because hospital environments can harbor fungal spores in ventilation systems and construction dust.
Symptoms to Recognize
Fungal pneumonia shares many symptoms with bacterial and viral pneumonia, which is one reason it’s often missed or diagnosed late. Common signs include cough (sometimes producing phlegm), fever, chills, shortness of breath, chest pain when breathing or coughing, and fatigue. Some people experience nausea, vomiting, or diarrhea. Adults over 65 and those with weakened immune systems may develop confusion or a lower-than-normal body temperature rather than a fever.
The key difference is timeline. Bacterial pneumonia often hits hard and fast. Fungal pneumonia frequently comes on gradually, with symptoms that linger for weeks and don’t respond to standard antibiotics. If you’ve been treated for pneumonia with antibiotics and aren’t improving, a fungal cause is one of the things your doctor should consider, especially if you have any of the risk factors above or have recently traveled to an area where endemic fungi are common.
How It’s Diagnosed
Diagnosing fungal pneumonia is more complex than diagnosing the bacterial type. Standard chest X-rays may show an abnormality, but CT scans are more useful. In aspergillosis, for instance, CT imaging may reveal dense, well-defined nodules sometimes surrounded by a hazy “halo” of inflammation, or cavities in the lung tissue. These patterns can point toward a fungal cause rather than a bacterial one.
Blood tests play an important role. One widely used test detects galactomannan, a sugar molecule released by Aspergillus as it grows. In patients with very low white blood cell counts, this blood test has a sensitivity of about 82% and specificity of 81%. Testing fluid collected directly from the lungs during a bronchoscopy is even more accurate, with sensitivity and specificity both around 88%. DNA-based testing (PCR) can also help, though a single negative result isn’t enough to rule out infection since it misses roughly 20% of cases.
In many situations, doctors combine imaging, blood markers, and direct samples from the lungs to build a diagnosis, particularly when a patient has known risk factors and isn’t responding to antibacterial treatment.
Treatment and Outlook
Fungal pneumonia is treated with antifungal medications rather than the antibiotics used for bacterial infections. The specific drug depends on which fungus is involved. For aspergillosis, the most common invasive type, first-line treatment typically involves a class of antifungals called azoles, which work by disrupting the fungal cell membrane so the organism can’t survive. An alternative option is a medication derived from amphotericin, which attacks the fungal cell wall through a different mechanism.
Treatment duration is significantly longer than for bacterial pneumonia. While a course of antibiotics for a standard bacterial lung infection might last 5 to 10 days, antifungal treatment often continues for weeks or months, depending on severity and how well the immune system recovers. Some patients, particularly transplant recipients on ongoing immunosuppression, may need extended or even lifelong antifungal therapy to prevent relapse.
The stakes are high for invasive infections. One-year survival for people with invasive aspergillosis is about 59% among solid organ transplant recipients and just 25% among stem cell transplant recipients. Aspergillosis is one of the four most commonly missed diagnoses found during intensive care autopsies, underscoring how difficult it can be to catch. Milder forms, particularly endemic fungal pneumonia in otherwise healthy people, have a much better prognosis and often resolve with a standard course of antifungal treatment or even on their own.
Reducing Your Risk
For most healthy people, no special precautions are needed. Your immune system handles routine fungal spore exposure without trouble. But if you’re immunocompromised, a few environmental measures can meaningfully reduce your exposure.
Avoid activities that kick up soil or dust in areas where endemic fungi are common, such as digging, gardening, or exploring caves with bat colonies. If you live near construction or demolition sites, keep windows closed and be aware that these activities disperse large amounts of fungal spores into the air. Hospitals take this seriously: guidelines call for sealing air intakes near construction zones, using high-efficiency filters, removing bird nests near ventilation systems, and controlling dust in areas where immunocompromised patients are housed. If you’re undergoing chemotherapy, recovering from a transplant, or managing HIV, ask your care team about any specific environmental precautions relevant to where you live.