Candida parapsilosis is a type of yeast, a single-celled fungus, that causes serious infections. It is one of the most frequently isolated Candida species globally, often ranking as the second or third most common cause of bloodstream fungal infections in hospitalized patients. While it typically lives harmlessly on the skin, its characteristics allow it to become a pathogen in vulnerable individuals. Its prevalence in healthcare settings and ability to spread easily contribute to its clinical importance.
Biological Profile and Natural Habitat
C. parapsilosis is classified as an opportunistic pathogen, causing disease when a person’s immune system is weakened or protective barriers are compromised. Unlike some other Candida species, this fungus is not an obligate human resident and thrives extensively in the natural environment. It can be found in soil, water, and on domestic animals and insects.
The yeast commonly colonizes human surfaces, particularly the skin and gastrointestinal tract, and is often isolated from the subungual space of human hands. Its pathogenicity is linked to its capacity to form robust biofilms, which are complex, surface-adhered communities of fungal cells encased in a protective matrix. This biofilm formation is problematic on abiotic surfaces such as medical devices.
Biofilms allow the yeast to adhere strongly to materials like plastic and metal used in catheters and implants. These protective layers shield the fungal cells from the body’s immune defenses and reduce the effectiveness of antifungal medications, making infections difficult to clear. C. parapsilosis can also rapidly multiply in specialized nutrient solutions, such as total parenteral nutrition (TPN), often administered to critically ill patients.
High-Risk Populations and Transmission Routes
A combination of host vulnerability and environmental factors places certain patient groups at higher risk for C. parapsilosis infection. The population at the greatest risk is very low- and extremely low-birth-weight neonates, especially those in neonatal intensive care units (NICUs). These infants have immature immune systems, compromised skin integrity, and often require prolonged use of indwelling devices, which facilitate fungal invasion.
Other vulnerable patients include those in adult intensive care units (ICUs) who require invasive procedures or devices. Individuals with central venous catheters (CVCs), feeding tubes, or other long-term indwelling devices are susceptible because the yeast readily forms biofilms on these foreign materials. This device-related risk is also high for patients who have received prosthetic devices, such as artificial heart valves or joint replacements.
Patients with suppressed immunity are a major risk group, including those with blood cancers, HIV, or those undergoing chemotherapy, radiation therapy, or organ transplantation. Recent abdominal surgery can increase risk, as the procedure may allow the yeast, which colonizes the intestinal tract, to enter other parts of the body. Prolonged or frequent use of broad-spectrum antibiotics is another contributing factor, as this eliminates beneficial bacteria that normally control fungal growth.
The primary route of transmission within a hospital setting is horizontal, often involving the hands of healthcare workers. Since C. parapsilosis colonizes human skin, personnel can inadvertently transfer the yeast to patients, especially during the insertion or manipulation of medical devices. This transmission is a key reason for nosocomial outbreaks and underscores the importance of strict hand hygiene protocols. The organism’s persistence in the hospital environment and its ability to grow in nutrient solutions like TPN complicate infection control efforts.
Clinical Manifestations of Infection
The infections caused by C. parapsilosis are known as invasive candidiasis, with severity depending on the site of infection. The most common and serious manifestation is fungemia, a bloodstream infection where the yeast circulates throughout the body. Systemic symptoms of fungemia include fever, chills, and signs of septic shock, and candidemia is a leading cause of bloodstream infections in hospitalized individuals.
A major concern is device-related infection, where the yeast colonizes the surface of an implanted object. Infections on central venous catheters can lead to persistent fungemia, which is often difficult to resolve without removing the contaminated device. The organism’s affinity for prosthetic materials also puts patients at risk for fungal endocarditis, which is inflammation of the heart’s inner lining and valves, particularly in those with artificial heart valves.
The yeast can also lead to focal infections when it spreads from the bloodstream. These manifestations include:
- Endophthalmitis, an infection of the eye characterized by visual disturbances and pain.
- Joint and bone infections, such as osteomyelitis and arthritis, particularly in patients with prosthetic joints.
- Fungal peritonitis, common in patients undergoing peritoneal dialysis.
- Meningitis, an infection of the membranes surrounding the brain and spinal cord.
The severity of C. parapsilosis infections is often compounded by the patient’s underlying health conditions, contributing significantly to morbidity and mortality in medically fragile groups.
Identification and Antifungal Management
Clinical laboratories typically identify C. parapsilosis by culturing a sample of the patient’s blood or affected tissue. The yeast grows well on standard fungal culture media, and specialized chromogenic media assist in initial identification and differentiation from other Candida species. Molecular methods, such as Polymerase Chain Reaction (PCR) and other rapid tests, are increasingly used to quickly identify the organism and detect genetic markers related to drug resistance.
Antifungal management often involves medications such as fluconazole (an azole) or echinocandins. A significant challenge is the organism’s capacity for developing reduced susceptibility or resistance to common antifungal agents. While fluconazole is often effective, strains with acquired resistance are emerging, sometimes due to specific gene mutations.
C. parapsilosis can show reduced susceptibility to echinocandins compared to other Candida species, and the presence of a biofilm significantly complicates drug penetration. Therefore, successful clearance often requires the physical removal of any infected medical device, such as a central venous catheter or prosthetic component. Treatment decisions must be guided by susceptibility testing to select the most effective antifungal agent and address the difficulty of treating the yeast within a biofilm.