Contributed by Matthew T. Chambers, MD, PhD and Bryan A. Stevens, MDFINAL DIAGNOSIS
Candidemia caused by the emerging pathogen Candida auris
DISCUSSION
There are several subspecies of Candida to consider within the ICU setting. The most common candidiasis is caused by Candida albicans, but an emerging pathogen of concern is Candida auris, which was the source of this patient’s candidemia.
C. auris was initially identified from an ear culture in Japan in 2009 (1). To date, it has been identified in more than 30 countries. The resources necessary to identify C. auris are not universally available, and its occurrence may be much more widespread than is currently known.
This pathogen is a cause for concern due to both its association with outbreaks in healthcare environments (e.g. ICUs) and documented mortality data of approximately 30-60% (2, 3). It is unclear whether the pathogen is a direct cause of mortality in these patients, as a retrospective study of numerous patients within an ICU setting in England was not able to identify the pathogen as a direct cause of death in any of the known cases (1); regardless, the pathogens ability to spread easily within an ICU setting and the associated mortality rate is the source of strong concern, until this organism is better understood.
Identification of the organism is challenging, as the required tools and expertise are not universally available among clinical laboratories, both within the United States and around the world. The CDC recommends that the gold standard for identification is either MALDI-TOF or nucleic acid sequencing (3). The CDC recognizes that some commercially available tools currently have limited capability in identifying the organism (e.g., Vitek ®), while others provide helpful information but are insufficient to diagnose C. auris (e.g., CHROMagar ™). For laboratories relying on automated biochemical methods for identification of Candida spp., it is critical to understand that Candida auris may be misidentified as other Candida spp. Two such examples include C. haemulonii and C. duobushaemulonii. Knowing when to refer a Candida isolate for definitive identification to rule-out Candida auris is critical for patient management.
Another concerning feature of C. auris is its widespread resistance to antifungals (1, 3). Resistance has been identified to the Azole class and Amphotericin B. Consequently, the Echinocandin class of antifungals (e.g., Caspofungin) is the current empiric drug of choice, pending susceptibility testing of each specific isolate. It’s worth noting that isolates with reduced sensitivity to the Echinocandins have been reported. Furthermore, Echinocandins have limited penetration into the CNS and are not excreted in the urine, which may limit the usefulness of these drugs in certain situations.
Overall, as C. auris continues to spread throughout the Unites States and globally, it will play a larger role in the hospital setting as well as the clinical laboratories supporting hospitals. As the resources necessary to identify C. auris are not universally available, it is important to know the limitations of a laboratory’s testing capabilities, and when to seek additional support from a reference laboratory.
REFERENCES
1. Which of the following Candida species is the most common source of candidiasis?
2. Which of the following Candida species is an emerging pathogen of concern associated with ICUs and a mortality of approximately 50%?
3. Which of the following options is the best method for identification of C. auris isolated from a patient specimen?
4. In a non-neutropenic patient, which of the following drug classes would be the best choice for candidemia caused by C. albicans?
5. In a non-neutropenic patient, which of the following drug classes would be the best choice for candidemia caused by C. auris?
Contributed by Matthew T. Chambers, MD, PhD and Bryan A. Stevens, MD
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