Candida auris has become a subject of increasing interest in the medical community worldwide. This emerging pathogen with a high potential for multidrug resistance has the ability to spread easily from one patient to another, making it difficult to treat or eradicate. Several hospital outbreaks have already been reported in South Asia, Europe and South America. Not surprisingly, it has been compared to the much dreaded multidrug resistant bacteria, earning a spot on the list of the world’s 10 most feared fungi, according to the journal Fungal Diversity.
The species was first described in Japan, in 2009, from an ear swab isolate (auris is the Latin word for ear). Soon afterwards, it was also reported from bloodstream infections in South Korea, India, Kuwait, Kenya and South Africa. By now, C. auris is reported from over 30 countries. In India, South Africa and Kenya C. auris has now become a common cause of candidemia.
Large-scale retrospective studies have retrieved almost no isolates from before 2009. It is possible that the increased consumption of antifungal medication has played a part in the recent emergence of C. auris as a pathogen, but this is probably not the only reason. Within the species, there exist 4 genetic lineages, corresponding to 4 apparent geographic centers of origin (East Asia, South Asia, South Africa and South America). This new virulent nature of C. auris thus should have developed simultaneously and independently in different continents.
Basic characteristics that set C. auris apart from most other Candida species, is the ability to grow at 42°C and at elevated salt concentrations. Also, it usually remains in a yeast-like state, without forming (pseudo)mycelium. The most common techniques applied in clinical laboratories to identify yeast, will often misidentify C. auris as Candida haemuloni or Candida lusitaniae. Reliable but, unfortunately, less frequently used methods are DNA sequencing and MALDI-TOF mass spectrometry, on the condition that the reference database is up to date and contains sufficient reference spectra of C. auris strains.
Colonization and infection
It is known from hospitals cases that C. auris can colonize the skin or other body parts without causing an infection. This colonization is often persistent and may extend to the patient’s environment (mattresses, walls, doorknobs, hospital equipment). This makes C. auris a micro-organism that is easily transmitted and difficult to eradicate, sometimes resulting in hospital outbreaks. Risk factors that may shift the balance from colonization to infection include: abdominal surgery, cancer, diabetes, central venous catheters, use of broad spectrum antibiotics, previous antifungal therapy. The reported mortality rates of infections due to C. auris vary between 30 and 60 %.
Difficult to treat
The general population of C. auris is considered to be resistant to fluconazole, the primary antifungal drug when a yeast infection is suspected. A rather large proportion is also resistant to amphotericin B, another main type of antifungal. The suggested first-line therapy for C. auris infections are echinocandins. Susceptibility testing of the isolated strain is highly recommended, not only to determine dosage, but also because some strains exhibit resistance also to echinocandins. Multidrug resistant fungi are a worrisome problem as the armamentarium to combat fungal pathogens is very limited.
The Belgian strain was isolated from a Kuwaiti woman who was referred to the Imelda hospital at Bonheiden after complicated bariatric surgery. Blood cultures revealed yeast colonies which were identified as C. auris by MALDI-TOF mass spectrometry. Contact precautions were activated to prevent further spread. Anidulafungin treatment was able to resolve the infection, but swabs of the rectum and nose demonstrated a persistent colonization with echinocandin-resistant C. auris. Nevertheless, the patient fully recovered. One of the initial isolates, taken from a catheter, was provided to BCCM/IHEM and is available with accession number IHEM 27689.
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