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22 Apr 2018

The emergence of Candida auris

Candida auris, an emerging species in the Candida family, is an increasingly concerning public health threat.

Heather Young and Mathilda Wilmot from the Microbiological Diagnostic Unit, the University of Melbourne, at the Doherty Institute

First reported in 2009, the species was identified when a single strain of a novel ascomycetous yeast species belonging to the genus Candida was isolated from the external ear canal of a Japanese inpatient [1]. Subsequently identified in South Korea as a causative agent of otitis media, a retrospective review of Candida strain collections in South Korea revealed that the earliest known strain of C. auris was isolated from the blood of a paediatric patient in 1996. It was not until 2011 however, that the potential to cause invasive infection was confirmed when it was isolated from the blood of three Korean patients with septicaemia [2].

Concurrent with the identification of these invasive cases in South Korea, C. auris was also isolated from 15 patients in a tertiary hospital in Northern India [3]. Since then, cases have been reported in at least 30 countries across all continents. Hospital outbreaks have also been recorded in 5 countries, including in a cardiothoracic centre in London between 2015 and 2016 – the largest identified outbreak in Europe so far [4]. In Australia, C. auris was first identified in 2015 in a Kenyan man who presented to hospital whilst visiting family in Perth, Western Australia [5]. No further cases were identified in Australia until August 2018, when C. auris was isolated from a Victorian patient who had spent time in United Kingdom hospital known to have had C. auris cases [6].

Somewhat surprisingly, molecular analysis of the strains collected from different geographic regions have revealed that C. auris has emerged independently in multiple regions of the world at roughly the same time. A 2016 study from the UK compared strains from India, Japan, South Africa, South Korea and Venezuela with strains from the London outbreak. Isolates from closely related sibling species C. haemulonii, C. duobushaemulonii and C. pseudohaemulonii were also included in the analysis as an outgroup. Cluster analysis showed that all species formed distinct clusters based on amplified fragment length polymorphism and that C. auris isolates that came from the same geographic region were clustered together [4]. Additionally, phylogenetic analysis from a 2012-2015 study conducted across three continents identified four distinct C. auris clades, comprised exclusively of isolates from Pakistan, India, South Africa, and Venezuela or Japan. Separated by tens of thousands of single nucleotide polymorphisms, each clade represented a distinct geographic region [7]. This distinct difference between clades, combined with the clonal nature of isolates within each clade, is further evidence for C. auris’ independent emergence simultaneously in multiple locations.

The emergence of this new species is concerning, particularly given the increased multi-drug resistance being reported. While C. auris is usually resistant to fluconazole, recent reports have also documented high level resistance to all 3 major classes of antifungal drugs, limiting treatment options and increasing the potential for outbreaks in healthcare settings [2] . This is further exacerbated by the difficulties in identifying C. auris, which requires specialised molecular techniques for accurate identification as it can be difficult to distinguish from other Candida species phenotypically.

Whilst invasive infections with any Candida spp. can be fatal, and there is little data comparing mortality rates of C. auris infection with other Candida spp, there are reports of C. auris case fatality rates as high as 72% [7]. Coupled with the difficulty in identifying and treating C. auris and its propensity to cause outbreaks in  healthcare settings, this emerging pathogen presents a serious public health threat that warrants global collaboration in surveillance and control efforts.

Further information on C. auris can be found here.