Fungal bloodstream infection, most commonly caused by species of the yeast Candida, is one of the most dangerous hospital-acquired infections, with death rates that can exceed 40% in intensive care settings. The medical term for Candida in the blood is candidemia, and it accounts for the vast majority of fungal bloodstream cases, though environmental molds and other yeasts can also reach the circulation in vulnerable people. The condition is overwhelmingly a problem for hospitalized patients, particularly those in ICUs with central venous catheters, weakened immune systems, or prolonged courses of broad-spectrum antibiotics.
Which Fungi Cause Bloodstream Infections
Candida species dominate. In ICU surveillance studies, virtually all yeast bloodstream infections are candidemia, with mold infections far less common but considerably deadlier when they do occur. An Italian multicenter survey of ICU patients found the incidence of yeast bloodstream infections was roughly seven times higher than that of invasive mold infections, but the crude mortality for mold infections reached about 62%, compared with an already-high overall mortality of around 43%.1PubMed Central. Epidemiology of invasive fungal infections in the intensive care unit: results of a multicenter Italian survey (AURORA Project)
Within Candida, the species landscape has shifted. Candida albicans used to be considered the dominant culprit, but in both adults and children, non-albicans species now make up the majority of cases. One large study found that roughly 57% of adult and 62% of pediatric Candida bloodstream infections were caused by non-albicans species.2PubMed Central. Candida albicans and Non-albicans Bloodstream Infections in Adult and Pediatric Patients: Comparison of Mortality and Costs Candida parapsilosis has become particularly common in ICU settings, partly because it has a strong tendency to colonize foreign body surfaces like catheters and parenteral nutrition lines.3PubMed Central. The fungal stronghold: biofilms in hemodialysis catheters, diagnostic pitfalls, and the challenge of catheter salvage Candida glabrata is another species of growing concern because it can carry inherent resistance to some antifungal drugs.
Outside of Candida, environmental fungi cause bloodstream involvement through a different route. Organisms like Aspergillus, Cryptococcus, Histoplasma, Blastomyces, and Coccidioides are inhaled from the environment and can disseminate to the blood in people with compromised immunity. Systemic infections from these environmental pathogens carry mortality rates as high as 90% and cost the U.S. healthcare system billions annually.4PubMed Central. How Environmental Fungi Cause a Range of Clinical Outcomes in Susceptible Hosts However, the overwhelming majority of fungal bloodstream infections that clinicians encounter day-to-day are candidemia in hospitalized patients, and that is the focus of most of the research and clinical guidance.
How Fungi Get Into the Blood
There are two main entry routes, and understanding them explains most of what follows about risk factors and prevention.
The first and most common pathway is through medical devices, especially central venous catheters (CVCs). Candida species are remarkably good at adhering to the plastic surfaces of catheters, where they form dense, layered communities called biofilms. More than 90% of catheter-related Candida bloodstream infections are linked to CVC use.5PubMed Central. Biofilm: The invisible culprit in catheter-induced candidemia Once a biofilm matures, the fungi secrete an extracellular matrix rich in a sugar polymer called beta-1,3 glucan. This matrix functions as a physical shield, trapping antifungal drugs and preventing them from reaching the organisms even when those organisms would be susceptible in a lab test.3PubMed Central. The fungal stronghold: biofilms in hemodialysis catheters, diagnostic pitfalls, and the challenge of catheter salvage The biofilm also harbors dormant “persister cells” that can survive antifungal treatment and reignite the infection after therapy stops.
The second major pathway is translocation from the gut. Candida normally lives in small numbers in the human gastrointestinal tract without causing harm. Problems arise when broad-spectrum antibiotics wipe out competing bacteria, allowing Candida to expand dramatically. If the gut lining is then damaged, as happens during chemotherapy-induced mucositis or critical illness, the overgrown Candida can cross into the bloodstream.6PubMed Central. Long-term Antibiotic Exposure Promotes Mortality After Systemic Fungal Infection by Driving Lymphocyte Dysfunction and Systemic Escape of Commensal Bacteria Research in animal models has shown something alarming about this pathway: when mice pre-exposed to antibiotics develop systemic candidiasis, gut bacteria also escape into the bloodstream alongside the fungus, compounding the infection with a simultaneous bacterial challenge.7Cell Host & Microbe. Broad-spectrum antibiotics promote invasive fungal infection by disrupting immune control in the gut
Who Is Most at Risk
A systematic review and meta-analysis of critically ill patients identified the factors carrying the highest odds of invasive Candida infection. Broad-spectrum antibiotics topped the list with roughly a fivefold increase in risk. Central venous catheters, total parenteral nutrition, prior Candida colonization, and blood transfusion each carried similar magnitudes of risk.8CHEST. Risk Factors for Invasive Candida Infection in Critically Ill Patients: A Systematic Review and Meta-Analysis A machine-learning analysis of ICU-acquired fungal infections independently confirmed several of these, adding corticosteroid use, arterial catheter placement, urinary catheters, enteral nutrition, and invasive mechanical ventilation as contributing factors.9PubMed Central. Identifying the risk factors of ICU-acquired fungal infections: clinical evidence from using machine learning
Neonates face their own distinct risk profile. Preterm and low-birth-weight infants in neonatal ICUs are especially vulnerable because their immune systems are immature and they often require the very interventions that promote fungal infection: prolonged antibiotics, central lines, parenteral nutrition, and corticosteroids. Poor adherence to infection control practices within the unit further raises the danger.10PubMed Central. Invasive Candida Infections in Neonatal Intensive Care Units: Risk Factors and New Insights in Prevention
Outside the hospital, people with hematological cancers, organ transplant recipients on immunosuppressive drugs, and individuals with advanced HIV are the groups most at risk for both candidemia and disseminated infections from environmental fungi.
Symptoms and Complications
Fungal bloodstream infections are notoriously hard to distinguish from bacterial sepsis at the bedside. The hallmark symptom is fever that does not respond to antibiotics. Patients already in the ICU may develop worsening hemodynamic instability, rising inflammatory markers like C-reactive protein and procalcitonin, or unexplained organ dysfunction. Standard blood tests like white blood cell counts are often unhelpful on their own for differentiating fungal from bacterial infection. Research has found that certain cytokine and chemokine levels in the blood are significantly elevated in patients with fungemia compared to uninfected controls, but these are not yet standard bedside tests.11PubMed Central. Diagnostic efficacy of serum cytokines and chemokines in fungal bloodstream infection in febrile patients
If candidemia is not treated promptly, the fungus can seed distant organs and cause secondary infections. In a study of 765 adults with candidemia, about 4% developed complications including eye infections, heart valve infections, or bone and joint infections.12PubMed. Clinical characteristics and risk factors for complications of candidaemia in adults: Focus on endophthalmitis, endocarditis, and osteoarticular infections Eye involvement (endophthalmitis) was the most common of these complications. Clinical guidelines recommend that every patient diagnosed with candidemia receive a dilated eye exam, because fungal seeding of the retina can threaten vision and may not produce obvious symptoms early on.13PubMed. Complications of Candidemia in ICU Patients: Endophthalmitis, Osteomyelitis, Endocarditis Endocarditis and osteomyelitis are rarer but require prolonged courses of antifungal therapy, sometimes months, and may need surgical intervention.
Diagnosing Fungal Bloodstream Infections
Blood cultures remain the standard diagnostic tool, but they are slow and imperfect. The time it takes for a blood culture to turn positive varies by Candida species and the amount of fungus in the blood. Some species, particularly Candida glabrata, can take significantly longer to grow, meaning clinicians may be waiting days before getting an answer.14Microbiology Society. Evaluation of three different bottles in BACTEC 9240 automated blood culture system and direct identification of Candida species to shorten the turnaround time of blood culture Blood cultures also have a sensitivity problem: they miss a meaningful proportion of true candidemia cases, which is why clinicians have looked for faster, more reliable alternatives.
One such alternative is T2Candida, a technology based on magnetic resonance that can detect the five most common Candida species directly from a whole blood sample in about five hours, without waiting for organisms to grow.15PubMed Central. T2Candida for the Diagnosis and Management of Invasive Candida Infections The test’s biggest strength is its negative predictive value: when it comes back negative, clinicians can be fairly confident the patient does not have candidemia, which can justify stopping empiric antifungal drugs earlier. In ICU patients with suspected candidemia, T2Candida testing was associated with a threefold increase in the odds of early and safe antifungal discontinuation compared to beta-D-glucan testing.16PubMed. T2 Candida versus beta-D-glucan to facilitate antifungal discontinuation in the intensive care unit
Beta-D-glucan (BDG) is a blood marker that detects a component of fungal cell walls. It has been widely adopted but comes with drawbacks. A comparison of two diagnostic practices at different hospitals found that adding BDG testing to blood cultures and T2Candida led to nearly 40% more antifungal days without measurable clinical benefit.17Diagnostic Microbiology and Infectious Disease. Utility of incorporation of beta-D-glucan and T2Candida testing for diagnosis and treatment of candidemia The BDG test’s positivity was interpreted inconsistently by clinicians, often leading to unnecessary treatment. This highlights a recurring theme in fungal diagnostics: more testing does not always translate into better outcomes, and the interpretation of results matters as much as the test itself.
On the frontier of diagnostics, next-generation sequencing (NGS) of cell-free DNA in blood plasma has shown early promise for identifying fungal pathogens without the need for culture. In small case series, plasma NGS correctly identified the same fungus found on tissue biopsy in the majority of patients, including molds like Aspergillus, Rhizopus, and Scedosporium that are extremely hard to grow in culture.18bioRxiv. Liquid biopsy for infectious diseases: Sequencing of cell-free plasma to detect pathogen DNA in patients with invasive fungal disease In pediatric immunocompromised patients, serial NGS testing corresponded to clinical response during treatment, suggesting it could eventually serve as a monitoring tool as well.19Open Forum Infectious Diseases. Serial Microbial Cell-Free DNA Next Generation Sequencing (NGS) As A Means of Diagnosis and Monitoring of Clinical Response To Treatment Of Invasive Fungal Infections (IFI) In Immunocompromised Pediatric Patients These technologies remain in relatively early stages of clinical adoption, but they represent a meaningful shift toward culture-independent diagnosis.
Treatment
Three classes of antifungal drugs carry the bulk of the treatment burden for candidemia: echinocandins, azoles, and polyenes.
Echinocandins, which include caspofungin, micafungin, and anidulafungin, are the recommended first-line treatment in most current guidelines. They work by disrupting the fungal cell wall and are generally well tolerated. A systematic review and meta-analysis comparing echinocandins to polyenes (primarily amphotericin B) for initial treatment of candidemia found that echinocandins were associated with lower mortality.20PubMed. Comparison of mortality between echinocandins and polyenes for an initial treatment of candidemia: A systematic review and meta-analysis They are also particularly valued in patients with liver disease or liver transplants, where other antifungals may be harder on an already damaged organ.21PubMed Central. Echinocandins for management of invasive candidiasis in patients with liver disease and liver transplantation
Azoles, particularly fluconazole, remain a viable option in certain clinical scenarios. A randomized trial in patients without neutropenia found that fluconazole and amphotericin B were not significantly different in their effectiveness at treating candidemia.22PubMed. A randomized trial comparing fluconazole with amphotericin B for the treatment of candidemia in patients without neutropenia A propensity-score analysis comparing echinocandins to azoles as first-line therapy in ICU patients found comparable treatment success and 90-day survival between the groups.23PubMed. Evaluation of first-line therapies for the treatment of candidemia in ICU patients: A propensity score analysis Fluconazole is often used as step-down therapy: a patient who is clinically improving and whose Candida isolate is susceptible can be transitioned from intravenous echinocandin to oral fluconazole to finish their treatment course, which may allow earlier hospital discharge.
Amphotericin B, the oldest of the three classes, remains the most broadly active antifungal available and is sometimes needed for resistant infections or those caused by unusual species. Its traditional formulation carries well-known toxicity to the kidneys, though lipid-based preparations have reduced this problem considerably. In a laboratory model of catheter-related candidemia, amphotericin B showed the strongest activity overall, though no drug regimen completely eradicated fungal colonization from the catheter surface.24PubMed Central. Antifungal activity of amphotericin B, fluconazole, and voriconazole in an in vitro model of Candida catheter-related bloodstream infection
The Catheter Question
Since catheters are the single most common entry point for Candida into the blood, a natural question is whether removing the catheter immediately changes outcomes. The answer is surprisingly contested. Most guidelines recommend early catheter removal in patients with candidemia, and there is logic behind it: the biofilm on the catheter cannot be sterilized by drugs alone. A Cochrane review of 73 observational studies found that 40 reported a beneficial effect of catheter removal, while 34 showed no clear difference, and none favored keeping the catheter in place.25Cochrane Database of Systematic Reviews. Central venous catheter removal for adults and children suffering from bloodstream infections caused by Candida species
However, the picture is muddied by the fact that sicker patients are often the ones whose catheters cannot be easily removed. When a large analysis of data from two randomized clinical trials adjusted for illness severity and other confounders, the apparent benefits of early catheter removal disappeared. Severity scores, age, and persistent neutropenia were the dominant predictors of outcome, not the timing of catheter removal.26PubMed. Early removal of central venous catheter in patients with candidemia does not improve outcome: analysis of 842 patients from 2 randomized clinical trials In practice, most infectious disease specialists still favor removing or replacing the catheter when feasible, since the Cochrane data leans in that direction and there is no study showing removal is harmful. But for patients who absolutely need continued central access, the data suggests that catheter retention is not a death sentence as long as appropriate antifungal therapy is in place.
Why Treatment Timing Matters
One of the clearest findings in candidemia research is that delays in starting antifungal therapy increase death rates. A multi-institutional study found a striking dose-response relationship: mortality was 15% when fluconazole was started on the day the positive blood culture was drawn, rising to 24% if started one day later, 37% at two days, and 41% at three or more days.27Clinical Infectious Diseases. Time to Initiation of Fluconazole Therapy Impacts Mortality in Patients with Candidemia: A Multi-Institutional Study In patients with candidemia-associated septic shock, the critical threshold was even tighter: those who received appropriate antifungal therapy within 15 hours of the first positive blood culture had significantly better survival.28PubMed. The effect of time to antifungal therapy on mortality in Candidemia associated septic shock
This creates a clinical dilemma. Blood cultures, the diagnostic standard, can take 24 to 72 hours or more to turn positive. By the time the lab confirms Candida, any delay in starting therapy has already begun. This is why clinicians in ICUs often start empiric antifungal therapy in high-risk patients with persistent fever, even before cultures confirm the diagnosis. Faster diagnostic tools like T2Candida may help narrow this gap, but in many hospitals, clinical judgment and risk-factor assessment still drive the decision to treat early.
The Candida Auris Problem
No discussion of fungal bloodstream infections would be complete without Candida auris, a species that barely existed in the clinical literature before 2009 and has since become a global public health emergency. C. auris is uniquely threatening for several reasons. It can persist on hospital surfaces and medical equipment for weeks, making it adept at causing outbreaks. It is often resistant to multiple classes of antifungal drugs, sometimes including echinocandins. And the crude in-hospital mortality rate of C. auris candidemia ranges from 30% to 60%, with infections typically developing weeks after hospital admission.29PLOS Pathogens. Candida auris: A rapidly emerging cause of hospital-acquired multidrug-resistant fungal infections globally
What makes C. auris especially alarming is how difficult it is to identify with standard laboratory methods. It is frequently misidentified as other Candida species by conventional biochemical tests, which means outbreaks may go undetected until specialized molecular testing is done. Hospitals that have experienced C. auris outbreaks have had to implement aggressive infection control measures, including patient screening, enhanced cleaning protocols, and cohorting of affected patients, to contain the spread.
Preventing Fungal Bloodstream Infections
Prevention strategies split into two broad approaches: reducing opportunities for fungi to enter the blood, and prophylactic antifungal drugs for the highest-risk patients.
On the infection-control side, the single most impactful intervention is rigorous catheter management. This means strict aseptic technique during insertion, daily reassessment of whether the catheter is still needed, and prompt removal when it is not. Hand hygiene, of course, underpins everything. For neonates, minimizing the duration of broad-spectrum antibiotic courses and parenteral nutrition has been identified as a key preventive strategy.10PubMed Central. Invasive Candida Infections in Neonatal Intensive Care Units: Risk Factors and New Insights in Prevention
Antifungal prophylaxis is standard in certain high-risk patient populations. In hematological malignancies, including acute leukemia and myelodysplastic syndromes, and in patients undergoing stem cell transplantation, prophylaxis is considered the gold standard and is backed by multiple prospective studies and society guidelines.30PubMed Central. Antifungal Prophylaxis in Immunocompromised Patients In organ transplantation, targeted prophylaxis is also employed. A single-center study of high-risk liver transplant recipients who received a 14-day course of caspofungin prophylaxis found that it was effective at preventing invasive Candida infections, though it did little to prevent invasive mold infections, which were likely already present at the time of transplant.31Open Forum Infectious Diseases. P-1936. Antifungal prophylaxis with echinocandin in high-risk liver transplant: a single-centre experience
How the Immune System Fights Back
For fungi that do enter the blood, the immune system mounts a response centered primarily on white blood cells called neutrophils. These cells are the body’s rapid responders to infection, and their importance in fungal defense is underscored by the fact that patients with prolonged neutropenia (very low neutrophil counts after chemotherapy, for example) face the highest risk of invasive fungal disease.
Research using real-time imaging in living animals has revealed a remarkable mechanism by which neutrophils defend the brain against Cryptococcus neoformans, a yeast that causes meningitis. Neutrophils were observed migrating to the fungal cells where they had become stuck on the inner lining of brain blood vessels, engulfing the organisms, and then carrying them back into the general circulation, effectively clearing the pathogen before it could cross into the brain tissue. When neutrophils were experimentally depleted, the fungal burden in the brain increased substantially.32Journal of Leukocyte Biology. Real-time in vivo imaging reveals the ability of neutrophils to remove Cryptococcus neoformans directly from the brain vasculature This helps explain why even short periods of neutropenia during cancer treatment create such a dangerous window for fungal invasion, and why restoring immune function is just as important as the antifungal drugs themselves in determining who survives a fungal bloodstream infection.