Cryptococcal meningitis is a fungal infection of the membranes surrounding the brain and spinal cord, caused by inhaling microscopic fungal cells found in soil, decaying wood, and bird droppings. It is one of the deadliest opportunistic infections in the world, responsible for an estimated 112,000 deaths each year, the vast majority among people living with HIV in sub-Saharan Africa. About 152,000 cases occur globally per year.
What Causes It
Two species of the fungus Cryptococcus are responsible for nearly all cases. The more common one, C. neoformans, is found worldwide in soil, weathered pigeon droppings, and the bark and hollows of dozens of tree species. The second, C. gattii, has not been found in bird droppings but thrives on and around certain trees, particularly eucalyptus. It was historically considered a tropical species but has established itself in temperate regions including British Columbia, the U.S. Pacific Northwest, and California.
Infection begins in the lungs. You breathe in dried fungal cells or spores, which are small enough to reach deep into the airways. In many people with healthy immune systems, the body contains the infection at this stage, sometimes without any noticeable illness. But in people whose immune defenses are compromised, the fungus can cross from the lungs into the bloodstream and eventually reach the brain, where it causes meningitis. This dissemination from lung to brain is the main driver of death from cryptococcal disease.
Who Is Most at Risk
Advanced HIV infection is by far the biggest risk factor. The fungus exploits the weakened immune surveillance that comes with low CD4 cell counts, which is why cryptococcal meningitis remains a leading cause of death among people with AIDS. But HIV is not the only pathway to this disease.
Solid organ transplant recipients face elevated risk because the anti-rejection medications they take, particularly corticosteroids, suppress the immune response the body needs to keep the fungus in check. Nearly half of non-HIV patients in one recent study were taking some form of corticosteroid therapy when they were first diagnosed. People being treated for autoimmune diseases, blood cancers, or other conditions requiring immune-suppressing drugs are also vulnerable. Interestingly, up to a third of patients with cryptococcal meningitis have no HIV and no other obvious reason for immune suppression. Some of these cases have been linked to specific genetic mutations or autoantibodies that quietly impair the body’s ability to fight fungi. C. gattii in particular is known for causing disease in people who appear otherwise healthy.
Symptoms and How It Develops
Unlike bacterial meningitis, which can strike within hours, cryptococcal meningitis typically builds over days to weeks. The onset is often subtle, which can delay diagnosis. The hallmark symptoms are headache and fever, but they frequently develop gradually rather than all at once.
As the infection progresses and pressure builds inside the skull, symptoms become more severe. You may experience nausea and vomiting, confusion, sensitivity to light, neck stiffness, and changes in vision. In transplant recipients and others on immunosuppressive drugs, fever and headache tend to appear earlier, which can actually lead to faster diagnosis and better outcomes in that group. In people without known immune problems, the symptoms may be vague enough that the correct diagnosis is not considered right away.
How It Is Diagnosed
The most reliable way to confirm cryptococcal meningitis is by testing cerebrospinal fluid, the liquid that surrounds the brain and spinal cord, collected through a lumbar puncture (spinal tap). A test called the cryptococcal antigen lateral flow assay detects proteins shed by the fungus and delivers results quickly. When performed on cerebrospinal fluid, this test has a pooled sensitivity and specificity of 99%, meaning it catches nearly all true cases and produces very few false positives.
The same antigen test can also be run on a blood sample, where it performs slightly less precisely but still well, with pooled sensitivity and specificity both around 96%. Blood-based screening is especially valuable in resource-limited settings for identifying people with HIV who have early cryptococcal disease before it reaches the brain, allowing preemptive treatment.
Treatment
Treating cryptococcal meningitis involves three phases: an aggressive initial phase to kill as much of the fungus as possible, a consolidation phase, and a long-term maintenance phase to prevent relapse.
The initial phase is the most intensive. The WHO’s 2022 guidelines recommend starting with a single high dose of a powerful intravenous antifungal (a form of amphotericin B) combined with two weeks of two oral antifungal medications. This approach was shaped by landmark clinical trials showing that combining amphotericin B with a drug called flucytosine significantly reduced death rates compared to using a different partner drug. In one major trial, patients who received the amphotericin-plus-flucytosine combination had a 10-week mortality rate of about 24%, compared to 45% with the alternative pairing.
The consolidation and maintenance phases rely on oral antifungal medication taken for months. This extended treatment is necessary because the fungus is difficult to fully eradicate and relapses are common without sustained suppression. One concern is that the fungus can develop partial resistance to the oral medication used during maintenance. A study from China found that about 40% of tested strains showed a phenomenon called heteroresistance, where small subpopulations of fungal cells can tolerate the drug even when the overall strain appears susceptible. Outright resistance has been reported in up to 10% of initial infections and 24% of relapse cases.
A Dangerous Complication for HIV Patients
People living with HIV face a unique and sometimes deadly paradox. Starting antiretroviral therapy (ART) is essential for long-term survival, but when the immune system begins recovering, it can mount an overwhelming inflammatory response against the fungus still present in the body. This is called immune reconstitution inflammatory syndrome, or IRIS.
Roughly 25% of people co-infected with HIV and Cryptococcus develop this complication within the first four months of starting ART, and it carries a mortality rate of around 20%. There are two forms. “Unmasking” IRIS occurs when ART reveals a cryptococcal infection that nobody knew was there, typically within two to six weeks of starting treatment. This is the deadlier form. “Paradoxical” IRIS happens in people already being treated for known cryptococcal meningitis who initially improve on antifungal therapy but then worsen one to six months after starting ART, as their recovering immune system triggers intense inflammation in the brain.
This is why the timing of ART initiation relative to antifungal treatment matters enormously. Clinicians generally delay starting ART for several weeks after beginning antifungal therapy to reduce the risk of IRIS.
Long-Term Effects in Survivors
Surviving cryptococcal meningitis does not always mean a full recovery. The infection and the elevated pressure it creates inside the skull can cause lasting neurological damage. Visual impairment is the most common long-term complication, affecting about 13% of survivors in one large review. It was particularly frequent in people infected with C. gattii, where nearly a third experienced vision problems. Visual complications present at the time of hospital discharge often persisted at follow-up appointments years later, with one study documenting ongoing impairment five years out.
Other lasting effects include limb weakness, hearing loss, recurrent seizures, and cognitive difficulties including learning problems that in some cases were still documented more than six years after the initial infection. Children and adults with HIV or other immune suppression were more likely to have neurological complications at discharge than those whose immune systems were suppressed by medications alone.