Candida Auris
- Article Author:
- Anna Sikora
- Article Editor:
- Farah Zahra
- Updated:
- 10/7/2020 2:08:35 PM
- For CME on this topic:
- Candida Auris CME
- PubMed Link:
- Candida Auris
Introduction
Candida auris is an emerging fungal pathogen that is associated with nosocomial infections and is considered a serious global health threat. It was first reported as a novel Candida species in 2009 and has been isolated in 35 countries in all continents, with the exception of Antarctica.[1][2]
C. auris may cause invasive infections associated with high mortality. It is considered a multi-drug resistant species, having variable resistance patterns to many typical antifungal agents used to treat other Candida infections. Yeast identification methods employed by laboratories typically misidentify C. auris as other yeasts making the detection and control of this pathogen challenging. The transmission of Candida auris occurs in nosocomial settings, even in those implementing infection prevention and control measures. In the United States, it is a nationally notifiable pathogen which allows for public health tracking and containing its spread.
Etiology
Candida auris is a yeast species belonging to the genus Candida. It is so named because it was first isolated from the external ear canal of a patient in a Japanese hospital.[1] Analysis of the yeast genomic DNA showed a distinct species with close phylogenetic profiles to Candida ruelliae, Candida haemulonii, C. duobushaemulonii, and C. pseudohaemulonii.[1][3]
C. auris is a budding yeast with cells that may be single, in pairs, or in groups. The cells are ovoid, ellipsoidal to elongate, and 2.5-5.0 micrometers in size. C. auris rarely forms hyphae or pseudohyphae, nor does it form germ tubes. However, growth under high-salt stress, such as on YTD (yeast extract, tryptone, and dextrose) plus 10% NaCl, and depletion of heat-shock proteins (HSP) can induce pseudohyphae like forms.[4][5] C. auris strain grows well at 40 degrees C but shows slow growth at 42C.[1] The colonial growth of C. auris on culture medium varies depending on the medium. On Sabouraud’s agar, C. auris will produce smooth and white to cream-colored colonies.[6] On CHROMagar, colonies of C. auris may display multiple color morphs ranging from pale to dark pink and rarely beige.
Epidemiology
Genetic analysis of C. auris isolates has demonstrated four distinct geographical clades: South Asian, East Asia, South African, and South American, with a possible fifth clade originating from Iran.[7] Genetic differences between the clades are suggestive that C. auris emerged independently in the aforementioned geographic locations.
The prevalence of Candida auris infection globally is unknown and likely underreported due to the lack of commercially available diagnostic methods and resemblance to other phenotypically related Candida species.[8] Since its original description in Japan in 2009, it has become widespread across all continents except Antarctica. A study that queried the international SENTRY Antifungal Surveillance Program sought to identify 15,271 candidemia isolates collected between 2004 to 2015 from 152 international medical centers (Asia, Europe, Latin America, and North America) showed that no Candida auris isolates were identified prior to 2009 and that the prevalence of C. auris was rare before 2009.[9] Further surveillance studies of misidentified samples recovered from South Korea in 1996, 2004, and 2006, and Pakistan in 2008 later detected C. auris.[10]
These studies suggest that C. auris emerged before 2009; however, the rapid global spread occurred afterward. By 2018, there were cases reported in the United States, Canada, Panama, Colombia, Venezuela, United Kingdom, Germany, Switzerland, Netherlands, France, Spain, Belgium, Norway, Russia, India, Pakistan, Bangladesh, Malaysia, China, Thailand, Singapore, Isreal, Kuwait, Oman, United Arab Emirates, Saudi Arabia, Iran, South Africa, Kenya, and Australia.[11] As of March 2020, the CDC has reported C. auris isolates in 41 countries. C. auris typically occurs in outbreaks in the nosocomial setting; however, sporadic cases have also been reported.
In the United States, the CDC has recorded 1092 cases of C. auris as of March 2020, with most cases occurring in New York City, New Jersey, and Illinois.[6] Epidemiologic information from these cases suggests that most strains were introduced from abroad and that these strains belonged to the clades of C. auris originating from South America and South Asia.[12] While the isolates themselves belong to distinct clades originated abroad, most cases acquired the infection in the United States in the health-care setting, which demonstrates clonal nosocomial transmission.[13]
Pathophysiology
Transmission
Candida auris is efficiently transmitted person-to-person.[14] The transmission of C. auris is different from most other Candida species, in that most candidiasis arises from the host’s microflora rather than acquisition from another person. C. auris is not considered a resident commensal organism and is not typically present within the human gastrointestinal tract, as are many other Candida species.[15] C. auris has a special predilection for skin, particularly the axilla and groin. It has the potential to colonize hosts within days to weeks of exposure, and invasive infections may occur within days to months after colonization.[16] Colonization with C. auris may persist for many months and possibly indefinitely.[17] It is, therefore, important to identify asymptomatic colonized patients to take additional precautions when these patients undergo placement of indwelling devices or surgical intervention. These patients may also be a source of transmission to other patients and environmental contamination.
C. auris can spread through contact with contaminated surfaces and fomites when shed from infected or colonized patients. Studies have found that C. auris may be found in patients' rooms and outside the patient’s rooms in hallways, chairs, beds, windowsills, counters, electrocardiogram leads, blood pressure cuffs, infusion pumps, and ventilators.[17] Shared multi-use patient equipment such as temperature probes and pulse oximeters may act as reservoirs of C. auris.[18] Laboratory studies of C. auris persistence show that it may survive for 7 days on moist or dry surfaces.[19] Another study showed that C. auris cells may remain viable for up to 4 weeks and culturable for 2 weeks.[20] Isolation and contact precautions should be used to prevent nosocomial transmission of C. auris.
Virulence Factors
Genetic studies of Candida auris have shown that a significant percentage of its genes are involved in central metabolism, which is a common trait among pathogenic Candida species allowing for the adaptation in divergent environments.[21] Candida auris has numerous virulence attributes that resemble those of C. albicans, such as enzyme secretion, nutrient acquisition, siderophore-based iron acquisition, tissue invasion, two-component histidine kinase system, and pathways involved in cell wall modeling.[22][23] Virulence factors may be strain-dependent. A study of 16 isolates of C. auris showed different levels of phospholipase and proteinase production.[24]
C. auris has also demonstrated the ability to evade the immune response. In a comparison study between Candida albicans and Candida auris, neutrophils preferentially targeted and killed C. albicans.[25] This same study showed that C. auris evaded neutrophil attack and the innate immune response, which is in line with another study showing that recognition and ability to stimulate cytokine release and phagocytosis were greater in C. albicans versus C. auris.[26]
C. auris also forms biofilms allowing for adherence to surfaces and plastic materials. Biofilm formation is also strain-dependent and C. auris shows reduced ability to adhere and form biofilms compared to Candida albicans, due to the rarity of pseudohyphae.[24][27]
In vitro studies have shown C. auris isolates may be aggregating or non-aggregating. The failure of C. auris to release daughter cells after budding results in a large aggregation of cells that is difficult to disrupt by detergent vortexing or detergent.[28] The property of aggregating strains is thought to promote survival in hospital environments. However, in vivo models have shown that the non-aggregating isolates exhibit more pathogenicity compared to aggregating isolates and have greater pathogenicity than C. albicans.[24][28] The thermotolerance of C. auris, growing optimally in temperatures of 37 degrees C and surviving in temperatures up to 42C also help certain strains persist in hospital environments.
Resistance Factors
Although C. auris can express the aforementioned virulence factors, the expression is weaker than other Candida species and the major factor contributing to its high mortality rates is its ability to develop resistance to multiple antifungal agents.[24] Biofilm formation allows for drug sequestration within the extracellular matrix, which confers antifungal tolerance observed in many Candida species.[29] A recent study showed that matrix sequesters nearly 70% of the available triazole antifungal, due to its rich mannan-glucan polysaccharides.[30]
Another study found that C. auris isolates with biofilms did not show susceptibility to any antifungal agent, including fluconazole, echinocandins, and polyenes compared to planktonic C. auris isolates, which were only resistant to fluconazole.[31] Genetic studies of Candida auris have shown expansions of genes linked to drug resistance and multidrug efflux.[3] Resistance to azoles and echinocandins is mediated by mutations in the genes encoding the lanosterol 14-alpha-demethylase (ERG11) gene and drug target 1,3-beta-glucan synthase (FSK1), respectively.[32] Efflux pumps such as the ATP-binding cassette (ABC) and major facilitator superfamily (MFS) also play a role in azole resistance.[23][33]
History and Physical
The clinical presentation of Candida auris infection is similar to that of other Candida species. C. auris has been isolated from different body sites including the nose, pharynx, sputum, lungs, pleural cavity, heart, blood, liver, abdominal cavity (peritoneal fluid), rectal or stool culture, urine, vagina, bone, axilla, groin, wounds/surgical tissue, pus, ear, and brain.[11][34]
Isolates from non-sterile body sites such as the genitourinary tract, skin and soft tissues, and lungs are likely a representative of colonization, rather than true infections.[6] Any indwelling devices, such as venous catheters, ports, urinary catheters, and prosthetic devices, should be examined for erythema, tenderness, and purulent material.
Clinical conditions that have been reported include bloodstream infections (fungemia), myocarditis, urinary tract infection, surgical wound infections, burn infections, skin abscesses (related to catheter insertion), otitis, meningitis, and bone infections.[1][10][35][36][37][38][39][40]
Compared to other Candida species, which are typical commensals of the gastrointestinal tract and not typically associated with the nosocomial transmission, C. auris has been shown to thrive on the skin.[16] C. auris forms a multilayer biofilm that proliferates best in the milieu that mimics sweaty axillary skin conditions.[41] Colonized patients are a source of transmission to other patients. Colonization may occur within a few hours to days of exposure, and invasive infections may occur within days to months after initial colonization.[16]
Risk factors associated with Candida auris infections are similar to those of other Candida species.[34] These risk factors include:
- Presence of a central venous catheter
- Indwelling urinary catheter
- Immunosuppressive state (human immunodeficiency virus, hematologic malignancy, solid tumors, transplant recipients, neutropenia, chemotherapy, corticosteroid therapy)
- Diabetes mellitus
- Chronic kidney disease
- Exposure to broad-spectrum antibiotics or previous exposure to antifungal agents within 30 days
- Concomitant bacteremia or candiduria
- Parenteral nutrition
- Blood transfusion
- Hemodialysis
- Surgery within 30 days
- Admission to intensive care units
Evaluation
The evaluation of suspected Candida auris infection starts with obtaining a clinical specimen from the site of infection. Specimens may be obtained from blood, urine, nose, pharynx, sputum, pleural cavity, heart, bile, peritoneal fluid, stool, vagina, bone, axilla, groin, wounds/surgical tissue, pus, ear, and cerebrospinal fluid and sent for culture, staining, and/or histopathologic evaluation. It is important to establish whether there is clinical evidence of a true infection, especially in the setting of cultures obtained from non-sterile sites, which may represent colonization. Growth of Candida species in blood culture systems typically takes 1 to 3 days and another 1 to 2 days for identification after subculture onto agar medium.
The identification of Candida auris has presented challenges for laboratories, and it is commonly misidentified using clinical microbiology methods. While the aforementioned phenotypic characteristics of Candida auris colonies in culture may be useful in identifying it, they cannot be used for definitive diagnosis. Many biochemical methods and automated testing methods commonly misidentify C. auris for other Candida species, notably C. haemulonii and other yeast species.[42]
The most accurate identification is made with devices using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with appropriate reference databases, which can differentiate C. auris from other Candida species.[43] Other molecular methods have also been developed and are based on sequencing the D1-D2 region of the 28s rDNA or the Internal Transcribed Region (ITS) of the rDNA.[8][44]
There is an automated molecular test using competitive DNA hybridization and electrochemical detection that is able to rapidly distinguish 15 fungal pathogens, including C. auris. A multi-center study showed that this testing method has a 100% sensitivity and specificity for C. auris, C. dubliniensis, C. famata, C. krusei, and was able to distinguish between other Candida species, including C. glabrata, C. lusitaniae, C. albicans, C. tropicalis, and C. parapsilosis.[45] The more accurate, reliable, and rapid forms of molecular tests are not always available in all facilities, which make the diagnosis, management, and infection control efforts challenging.
Treatment / Management
The most challenging aspect of managing invasive Candida auris infections is the level of drug resistance and the ability to develop drug resistance to the main three classes of antifungals, as previously discussed. A study from India investigated the susceptibility patterns of 350 C. auris isolates and showed that 90% were resistant to azoles (fluconazole), 8% were resistant to polyene (amphotericin B), and 2% were resistant to echinocandins (anidulafungin and micafungin).[32] The study showed that overall, 25% of isolates were multidrug-resistant, and 13% of the isolates were multi-azole resistant.[32] The Centers for Disease Control and Prevention breakpoint analysis of isolates in the United States showed exceptionally high minimal inhibitory concentration (MIC) for azoles, echinocandins, polyenes, and nucleoside analogs.[46]
There is no concrete documentation for therapeutic options of C. auris infection. Most cases are managed on a case-by-case basis with guidance of susceptibility testing. It is highly recommended that consultation from an infectious disease specialist is obtained. Treatment of C. auris should be started only in the presence of clinical disease and should be avoided in patients that are colonized with C. auris when isolated from non-invasive sites (respiratory tract, urine, skin).[11]
The CDC has published tentative guidelines for initial therapy.[11] Adults and children greater than 2 months of age may be started on echinocandin therapy with caspofungin or micafungin. Anidulafungin may be used in adults but is not approved for use in children and should be avoided in this age category. Monitoring for clinical improvement, repeat blood culture to ensure clearance of fungemia, and repeat susceptibility testing should be conducted as resistance to echinocandins may develop. In clinically unresponsive patients, liposomal amphotericin B may be considered. In neonates and infants less than two months of age, the initial choice of antifungal therapy is amphotericin B deoxycholate, followed by liposomal amphotericin B. Echinocandins may be used with caution if central nervous system involvement is ruled out.
Apart from timely antifungal therapy, the management of candidemia involves the removal of central venous catheter or other indwelling devices and drainage of collections as soon as possible. In the setting of repeated positive blood cultures, a search for a metastatic focus should be done to rule out endocarditis, suppurative thrombophlebitis, or abscess formation. Nonneutropenic patients with candidemia should undergo a dilated ophthalmologic eye examination within the first week of diagnosis and one week after recovery from neutropenia in neutropenic patients to evaluate for endophthalmitis, chorioretinitis, and vitritis. Repeat blood cultures should be performed daily or every other day, to establish clearance of candidemia. The Infectious Disease Society of America guidelines recommends continuing antifungal therapy for two weeks after the blood cultures remain negative in patients without obvious metastatic complications.[47]
Prevention of invasive infection in colonized individuals involves minimizing the entry of the organism into sterile body sites. Ensuring appropriate use of medical devices, such as central venous catheters, indwelling urinary catheters, and maintenance of tracheostomy sites is needed. Continuous assessment of the need for such invasive lines and tubes followed by prompt removal are basic strategies to mitigate the risk of introducing organisms to sterile sites. Patients undergoing surgical procedures should have meticulous skin preparation with an alcohol-based agent.[11]
Differential Diagnosis
Candida albicans, Candida glabrata, Candida tropicalis, Candida paratropicalis, and Pichia kudriavzevii make up 95% of all invasive fungal infections.[2] While these pathogens are more common, infections with Candida auris occur at a higher incidence in primary and acquired immunosuppression compared to other fungal pathogens. However, infection in immunocompetent hosts also occurs, and the mere clinical presentation is insufficient to distinguish among Candida species.
The phenotypic characterization, such as appearance and color of C. auris colonies in culture, high tolerance to growth in both high heat (up to 42C), and saline environments, helps distinguish it from other Candida species but should not be used as the sole method for identification. Phenotypic platforms typically mistake C. auris for C. haemolonii, as well as other yeasts (C. famata, C. guilliermondii, C. lustaniae, C. parapsilosis, C. sake, Sacchromyces cerevisiae, and Rhodotorula glutinis). Molecular methods of identification are the standard-of-care testing for a definitive diagnosis of C. auris.
Prognosis
The mortality rate of invasive infections associated with C. auris is comparatively higher than that of other Candida species. The crude mortality rate associated with C. auris infections ranges from 30% to 72%.[9][48][49][50] The variable mortality rate data may be due to several factors, including the extent of the infection, age, associated risk factors, and co-morbid conditions. Infections have been reported in preterm infants to the elderly.[34] Pediatric populations showed a higher likelihood of survival.[51] Early identification of Candida auris and prompt treatment with appropriate anti-fungal regimens are associated with higher survival.[10]
Complications
The complications of invasive Candida auris infection are broad depending on the extent of the infection, host co-morbidities, and resistance patterns. While the most common presentation of Candida auris infection occurs as a bloodstream infection (fungemia), it may spread hematogenously to seed different organs and cause multi-organ dysfunction. Conversely, a localized infection may eventually turn into an overwhelming bloodstream infection and have further complications such as sepsis, multi-organ system failure involving the kidneys, heart, lungs, eyes, brain, liver and spleen, and ultimately death.
Deterrence and Patient Education
Given the high rates of transmissibility and antifungal resistance patterns, C. auris was declared a public threat by the Centers for Disease Control and Prevention (CDC). In June 2016, the CDC announced to clinicians, infection control practitioners, laboratories, and public health authorities about Candida auris, making all cases in the United States reportable to the authorities and the CDC.[6] The CDC has outlined various aspects of infection control and prevention of C. auris.
Hand hygiene is the basic component of infection control. Healthcare personnel should follow standard hand hygiene principles to control the spread of C. auris.[17] The preferred alcohol-based hand rubs are effective against C. auris, as are chlorhexidine hand rubs when hands are not visibly soiled.[52] When hands are visibly soiled, they should be washed with soap and water. Contact precautions with gowns and gloves should be worn. Gloves do not substitute hand hygiene.
The recommendations for infection control of C. auris are adapted from infection control strategies for Clostridium difficile infections and other multidrug-resistant organisms, which also show swift nosocomial spread. Infection control is applied to both infected and colonized individuals since both pose a risk of transmission.
Transmission-based precautions are implemented in acute care hospitals, long term acute care hospitals, and nursing homes, including skilled nursing facilities with ventilator units. In the acute care setting, contact precautions are recommended, and in skilled nursing facilities, either contact precautions or enhanced barrier precautions are used. Contact precautions include the use of gloves and gowns for healthcare personnel, single room placement, and placing patients in cohorts patients with only C. auris infection or colonization in non-single occupancy rooms or specific wings of a hospital.[12] Of note, patients with C. auris should not be in a cohort with patients having other multidrug-resistant organisms, besides C. auris. Patients may remain colonized with C. auris for months, even after the treatment and resolution of an acute infection. It is recommended that the patient stays on contact precautions for the duration of their hospitalization. Routine assessment for colonization is not recommended by the CDC. However, patients with a prolonged hospital stay or residing in nursing homes may be screened 3 months after the last C. auris-positive test and if no longer on antifungal therapy for at least one week or receiving topical antiseptic for 48 hours. Discontinuation of contact precautions may be considered if the patient has had two negative colonization tests at least one week apart.
C. auris may persist in the healthcare environment on a variety of surfaces.[19] Environmental disinfection of the patient’s room and other areas where care is received should be performed daily. Equipment that is being shared between patients should be thoroughly cleaned and disinfected. Fungicidal products that are effective against other Candida species and quaternary ammonia compounds may not necessarily be effective against C. auris.[53] Ultraviolet light, commonly used for environmental disinfection, does not appear to be effective against C. auris.[54] In vitro studies have shown that sodium hypochlorite and hydrogen peroxide are effective against C. auris.[52] [53][55] Environmental studies have found that rooms cleaned with sodium hypochlorite and hydrogen peroxide vapor were effective.[12][56]
Enhancing Healthcare Team Outcomes
Candida auris is an emerging fungal pathogen that is associated with nosocomial infections and is considered a serious global health threat. Epidemiologists both globally and in healthcare settings are crucial for monitoring the spread of this pathogen. C. auris has numerous virulence qualities, shows multi-drug resistance patterns to common antifungal therapy used for other invasive Candida infections, and has been challenging for microbiology laboratories to diagnose. All medical staff, including nurses, clinicians, medical technicians, and laboratory technicians, should be aware of the seriousness of this pathogen.
Staff should be educated on the recommendations for the disinfection of patient rooms and contaminated environments. Infectious disease specialists should collaborate with microbiology technicians in diagnosing patients and obtaining appropriate antibiogram information to be able to effectively manage infected patients. C. auris tends to occur in cluster breakouts in the healthcare setting and carries a high mortality. The infection prevention and control officer of the healthcare facility should be immediately notified and guide staff for appropriate infection control techniques and prevention of spread. C. auris is a reportable pathogen and should be reported to the Centers for Disease Control and Prevention.