Recommendations for Identification of Candida auris
Healthcare facilities or laboratories that suspect they have a patient with C. auris infection should contact state or local public health authorities and CDC (firstname.lastname@example.org) immediately for guidance.
CDC recommends that all Candida isolates obtained from a normally sterile site (e.g., bloodstream, cerebrospinal fluid) be identified to the species level so that appropriate initial treatment can be administered based on the typical, species-specific susceptibility patterns.
Approximately 54% of C. auris cases have been identified from blood; the remaining 46% of cases were identified in other body sites, including, but not limited to, urine, wounds, sputum, and bile. Some clinical laboratories do not typically determine the species of isolates from non-sterile sites since presence of Candida in these sites may represent colonization rather than infection and would not require treatment. However, C. auris is important to identify even from a non-sterile body site because presence of C. auris in any body site can represent wider colonization, posing a risk for transmission and requiring implementation of infection control precautions. Species identification for Candida isolates from non-sterile sites should be considered in certain circumstances, including:
- When clinically indicated in the care of a patient.
- When a case of C. auris infection or colonization has been detected in a facility or unit, in order to detect additional patients colonized. Species identification of isolates from non-sterile sites can be implemented for at least one month until no evidence exists of C. auris transmission.
- When a patient has had an overnight stay in a healthcare facility outside the United States in the previous one year in a country with documented C. auris transmission, especially those countries to which U.S. cases have been linked (India, Pakistan, South Africa, and Venezuela). Colonization for longer than a year has been identified among some C. auris patients; therefore hospitals might also consider determining the species for Candida isolated from patients with more remote exposure to healthcare abroad.
C. auris can be misidentified as a number of different organisms when using traditional biochemical methods for yeast identification such as VITEK 2 YST, API 20C, BD Phoenix yeast identification system, and MicroScan.
The table below summarizes common misidentifications based on the identification method used. If any of the species listed below are identified, or if species identity cannot be determined, further characterization using appropriate methodology (see “How to identify Candida auris“) should be sought.
|Identification Method||Organism C. auris can be misidentified as|
|Vitek 2 YST||
Rhodotorula glutinis (characteristic red color not present)
|BD Phoenix yeast identification system||
*C.. guilliermondii, C. lusitaniae, and C. parapsilosis generally make hyphae or pseudohyphae on cornmeal agar. If hyphae or pseudohyphae are not present on cornmeal agar, this should raise suspicion for C. auris as C. auris typically does not make hyphae or pseudohyphae. However, some C. auris isolates have formed hyphae or pseudohyphae. Therefore, it would be prudent to consider any C. guilliermondii, C. lusitaniae, and C. parapsilosis isolates identified on MicroScan as possible C. auris isolates and forward them for further identification.
Please note that this list is based on current knowledge about C. auris misidentification. It may change from time to time as we learn more about misidentification of C. auris.
An increase in infections due to unidentified Candida species in a patient care unit, including increases in isolation of Candida from urine specimens, should also prompt suspicion for C. auris, since C. auris can be transmitted in healthcare settings.
The appearance and color of C. auris colonies in culture may aid in species identification, but cannot be used as the only identification method for C. auris since C. auris cannot be distinguished from other more common species of Candida without using other methods described in the section below. C. auris is a budding yeast, which almost never forms short pseudohyphae and does not form germ tubes. Some strains form aggregates of cells, whereas others do not. Unlike most other Candida species, it grows well at 40–42º C on CHROMagar, C. auris colonies appear white, pink, or red, and some colonies cannot be distinguished from C. glabrata.
Laboratories with capability to characterize isolates further are encouraged to do so; CDC and some state and regional public health laboratories can also assist with characterizations when local capacity does not exist. All confirmed isolates of C. auris should be reported to local and state public health officials and CDC at email@example.com.
Diagnostic devices based on matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) can differentiate C. auris from other Candida species, but not all the reference databases included in MALDI-TOF devices allow for detection. Currently, accurate identification of C. auris can be performed using Bruker Biotyper brand MALDI-TOF using their “research use only” databases and VITEK (MALDI-TOF) MS RUO (with Saramis Ver 4.14 database and Saccharomycetaceae update).
Molecular methods based on sequencing the D1-D2 region of the 28s rDNA or the Internal Transcribed Region (ITS) of rDNA also can identify C. auris.
As C. auris continues to gain recognition, updated versions of other yeast identification platforms may be able to identify C. auris; please consult the instrument manufacturer for more information. When in doubt, please forward suspected C. auris specimens to CDC or state or regional public health laboratories for further characterization. Isolates should be submitted on slants shipped at room temperature. C. auris can grow on blood or chocolate agar slants; mycology specific media are not necessary if the laboratory does not have them. All confirmed isolates of C. auris should be reported to local and state public health officials and to CDC at firstname.lastname@example.org.
Antifungal susceptibility testing for Candida auris
All C. auris isolates should undergo antifungal susceptibility testing. Although C. auris is commonly multidrug resistant, levels of antifungal resistance can vary widely across isolates.
There are currently no established C. auris-specific susceptibility breakpoints. Therefore, breakpoints are defined based on those established for closely related Candida species and on expert opinion. Correlation between microbiologic breakpoints and clinical outcomes is not known at this time. For this reason, the information below should be considered as a general guide and not as definitive breakpoints for resistance. Please note that a finding of an elevated minimum inhibitory concentration (MIC) for an antifungal drug should not necessarily preclude its use, especially if the use of other antifungal drugs for the patient has been ineffective.
|Class/Drug||Tentative MIC Breakpoints (µg/mL)||Comment|
|Fluconazole||≥32||Modal minimum inhibitory concentration (MIC) to fluconazole among isolates tested at CDC was ≥256; isolates with MICs ≥32 were shown to have a resistance mutation in the Erg11 gene, making them unlikely to respond to fluconazole.|
|Voriconazole and other second generation triazoles||N/A||Consider using fluconazole susceptibility as a surrogate for second generation triazole susceptibility assessment. However, isolates that are resistant to fluconazole may respond to other triazoles occasionally. The decision to treat with another triazole will need to be made on case-by-case basis.|
|Amphotericin B||≥2||Recent pharmacokinetic/pharmacodynamic analysis of C. auris in a mouse model of infection indicates that under standard dosing, the breakpoint for amphotericin B should be 1 or 1.5, similar to what has been determined for other Candida species. Therefore, isolates with an MIC of ≥2 should now be considered resistant. If using Etest for amphotericin B and an MIC of 1.5 is determined, that value should be rounded up to 2.|
|Anidulafungin||≥ 4||Tentative breakpoints are based on the modal distribution of echinocandin MICs of approximately 100 isolates from diverse geographic locations.|
Based on these MIC breakpoints, some C. auris isolates from outside of the United States have been found to be resistant to all three classes of antifungal drugs, and many isolates are frequently resistant to multiple classes of drugs. In the United States, about 90% of C. auris isolates have been resistant to fluconazole, 30% have been resistant to amphotericin B, and a 5% have been resistant to echinocandins. These proportions may change as isolates are tested.
All laboratories, especially laboratories serving healthcare facilities where cases of C. auris have been detected should do the following:
- Review past microbiology records (as far back as 2015, if possible) to identify cases of confirmed or suspected C. auris (see When to suspect C. auris infections).
- Conduct prospective surveillance to identify C. auris cases in the future.
- Consider screening close contacts of patients with C. auris for presence of colonization.
- Page last reviewed: September 14, 2017
- Page last updated: October 24, 2017
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