Invasive candidiasis is a serious fungal infection in which Candida yeast enters the bloodstream or internal organs. Unlike common yeast infections on the skin or in the mouth, this form affects deep tissues like the kidneys, liver, spleen, heart valves, and even the brain. It carries a 30-day mortality rate between 28% and 55% depending on the patient population, making it one of the deadliest hospital-acquired infections. It almost exclusively affects people who are already critically ill or have weakened immune systems.
Candidemia vs. Deep-Seated Infection
The term “invasive candidiasis” covers two overlapping situations. The first is candidemia, which means Candida is circulating in the bloodstream. This is the most common form and the one most frequently detected because blood cultures can pick it up. The second is deep-seated candidiasis, where the fungus has already spread to one or more organs. These two forms often occur together: Candida enters the blood and then seeds distant organs.
Common sites where the fungus takes hold include the eyes (causing a condition called chorioretinitis that can threaten vision), the kidneys, the liver, the spleen, and the heart valves. In rare cases, the fungus crosses into the central nervous system. When it spreads to multiple organs simultaneously, the result can be sepsis and multiorgan failure.
How Candida Invades the Body
Candida normally lives harmlessly on your skin and in your gut. Problems start when the fungus gets past the body’s natural barriers. This can happen through a break in the gut lining (from surgery, for example), through a contaminated catheter inserted directly into a vein, or when the immune system is too suppressed to keep the fungus in check.
Once inside, Candida albicans (the most common species) shifts from a round yeast form into long, thread-like structures called hyphae. These hyphae are the fungus’s invasion tools. They physically push through cell layers by forcing the cell to build a tunnel of structural protein around the intruding filament, allowing the fungus to pass through without immediately destroying the cell. At higher concentrations, the hyphae become more destructive, breaking apart the tight junctions that hold cell layers together and creating gaps that let even more fungus through. This is how Candida can eventually penetrate protective barriers like the lining of blood vessels and, in severe cases, the barriers protecting the brain.
Who Is at Risk
Invasive candidiasis is not a community infection. It overwhelmingly affects people already hospitalized, particularly those in intensive care units. A large meta-analysis of critically ill patients identified several factors that dramatically increase risk:
- Broad-spectrum antibiotics carried the highest risk, roughly 5.6 times the odds of developing the infection. These drugs wipe out competing bacteria in the gut, giving Candida room to overgrow and eventually cross into the bloodstream.
- Blood transfusions raised the odds about 4.9 times.
- Candida colonization (Candida already growing in sputum, stool, or other sites) increased risk about 4.7 times.
- Central venous catheters also carried about 4.7 times the odds. Candida readily forms biofilms on the surface of these devices, creating a direct pipeline into the bloodstream.
- Total parenteral nutrition (IV feeding) raised risk about 4.6 times, partly because the lipid-containing solutions promote Candida growth and biofilm formation.
Abdominal surgery, mechanical ventilation, dialysis, diabetes, and chemotherapy are also significant risk factors. Surgery and chemotherapy can damage the body’s natural barriers, while conditions like diabetes impair immune function. The more of these factors a patient has, the higher the cumulative risk.
Symptoms and What It Looks Like
Invasive candidiasis is difficult to distinguish from bacterial sepsis based on symptoms alone. Most patients develop fever that doesn’t respond to antibiotics, which is often the first clue that a fungal infection may be involved. Beyond that, symptoms depend on which organs are affected.
Skin involvement can produce scattered pustules from the fungus spreading through the blood to the skin’s surface. Eye involvement may cause blurred vision or eye pain. Kidney or liver infections may show up as worsening organ function on lab tests without an obvious bacterial cause. In the most severe cases, the infection progresses to full sepsis with dropping blood pressure, rapid heart rate, and failure of multiple organ systems. Because these symptoms overlap with so many other critical illnesses, diagnosis depends heavily on lab testing.
Why Diagnosis Is Challenging
Standard blood cultures, the most basic diagnostic tool, miss about half of all invasive candidiasis cases. Even when cultures do turn positive, they can take days, and the infection may be well advanced before results come back. This delay is a major contributor to the high mortality rate.
To improve detection, hospitals use a blood test that measures beta-D-glucan, a sugar molecule found in fungal cell walls. When levels are elevated, it suggests an invasive fungal infection is present. The best-performing version of this test reaches about 85% sensitivity at optimized thresholds, meaning it catches roughly 85 out of 100 true cases. The trade-off is specificity: only about half the time a positive result comes back does it actually reflect invasive candidiasis, since other conditions can also raise beta-D-glucan levels. Clinicians typically combine blood cultures, beta-D-glucan testing, and clinical judgment to make the diagnosis.
Treatment With Antifungal Medications
A class of antifungal drugs called echinocandins is the standard first-line treatment for nearly all forms of invasive candidiasis. These medications work by disrupting the fungal cell wall, and they’re effective against most Candida species with relatively few side effects. They’re given intravenously, typically for at least two weeks after the last positive blood culture, though deep-seated organ infections require longer courses that can stretch to several weeks or months.
For patients whose infection has reached the eyes or the central nervous system, echinocandins don’t penetrate well enough. In those cases, doctors use different antifungals that can cross into these protected compartments. Once the infection is under control and the specific Candida species is confirmed to be susceptible, some patients can be transitioned from IV medication to an oral antifungal to complete treatment.
If the infection is linked to a central venous catheter, removing or replacing that catheter is a critical part of treatment. The biofilm that Candida forms on catheter surfaces is extremely difficult to eradicate with drugs alone, and leaving the catheter in place significantly reduces the chances of clearing the infection.
Mortality and Outcomes
Even with treatment, invasive candidiasis kills a substantial number of patients. Across multiple studies, the 30-day mortality rate typically falls between 28% and 40%, with some populations reaching as high as 55%. In patients with severe disease, one study documented 30-day mortality at nearly 69%. Mortality continues to climb over time: one large study found that 28-day mortality of 47% increased to 60% at six months.
Much of this mortality reflects the fact that patients who develop invasive candidiasis are already critically ill. But delays in diagnosis and treatment independently worsen outcomes. Every day that passes between the onset of candidemia and the start of effective antifungal therapy reduces survival. This is why hospitals with high-risk patient populations increasingly use prophylactic antifungals and risk-scoring tools to identify patients who might benefit from early treatment before cultures come back.
The Growing Threat of Candida Auris
One species has raised particular alarm in recent years. Candida auris, first identified in 2009, is resistant to most available antifungal drugs. In the United States, roughly 90% of C. auris isolates are resistant to fluconazole (the most commonly used oral antifungal), and about 30% are resistant to amphotericin B, a powerful IV medication traditionally used as a backup option. Resistance to echinocandins, currently the preferred treatment, is also increasing.
Unlike most Candida species, C. auris spreads easily between patients in healthcare settings and can survive on surfaces for weeks. It has caused outbreaks in hospitals and long-term care facilities on every inhabited continent. Its combination of drug resistance, environmental persistence, and difficulty in identification with standard lab methods has led the CDC to classify it as an urgent antimicrobial resistance threat.