Candida auris: A Stealth Enemy With Environmental Persistence
By Kelly M. Pyrek
Public health entities such as the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) have compiled lists of the problem pathogens that continue to represent some of the greatest challenges to infection prevention and control (IPC) efforts. Rising on that list is Candida auris, an emerging worldwide public health scourge that is growing in intensity as a healthcare-acquired organism. It is particularly fearsome because of its innate resistance to multiple anti-fungal drugs and its resilience in the face of traditional hygiene measures.
In contrast to other Candida species, C. auris is transmitted easily in the healthcare setting, and it is demonstrating the ability to persist both in the human host and on inanimate surfaces.
“Candida auris is an emerging fungus and one of the headaches with this species is it’s multidrug-resistant, meaning that it is resistant to multiple antifungal drugs commonly used to treat Candida infections,” confirms Rodney E. Rohde, PhD, MS, professor and chair of the Clinical Laboratory Science Program at Texas State University.
“Infection prevention experts tend to want to group pathogens into groups such as healthcare-acquired or community-acquired but when it comes to resistant organisms you really can't use those terms anymore,” Rohde says. “For instance, in some of the studies I have conducted with different organisms, what we used to think was only in the community, we see those strains or genotypes showing up in healthcare patients, and vice versa. So, even though microbiology and science tells us certain species are strictly found in the healthcare setting or strictly found in the community setting, in reality, it’s more of a global presence now due to so many vehicles and vectors that move in and out of healthcare settings.”
Rohde continues, “When we talk healthcare settings, we tend to only think hospitals, but we must think long-term care, outpatient and dialysis centers, clinics, and school and university health centers. I think it’s a communication problem; as scientists, we love to put things into pots and think we’ve described them adequately, and they are going to stay that way, but one of my favorite sayings is, organisms do not read the book of rules we’ve written for them. However, we teach it that way sometimes to try to make sense of it, but when you get into the real-world trenches, the truth is, we’re not able to do that. Organisms are crossing all boundaries.”
Candida auris as a newly recognized cause of fungal infection is catching healthcare professionals unawares, despite cases being reported for nearly a decade now. Since the first official isolation of Candida auris in 2009, scientific community has witnessed an exponential emergence of infection episodes and outbreaks in different world regions. According to the CDC as of June 30, 2019 (the most recent data available), there are 725 confirmed cases, plus an additional 1,474 patients have been found to be colonized with C. auris by targeted screening in 10 states with clinical cases.
“Candida, as a fungus, is an unusual and a difficult problem to deal with,” Rohde says. “It’s not typically something you would be looking for in a healthcare setting, and certainly not looking for it in the common population. But it is a factor when looking at the immunocompromised population in context of environmental and healthcare exposure; for example, could a patient have been working in a certain environment where fungi and yeast are present? But to have a fungus emerging and breeding in a healthcare setting is a novel challenge in our lifetime. So, I think we are trying to grasp what that means.”
He continues, “Microbiologists are very concerned about C. auris because you almost have to rethink everything from the laboratory perspective. If you are a clinician in a smaller facility or a rural hospital, you often must wait on sending specimens out to an off-site, more central clinical laboratory, and that eats up valuable diagnostic time. You can typically know pretty quickly if you have Staph or Klebsiella or any of these other multi-resistant organisms if you have access to rapid assays; but yeast and fungi are not typically, at least right now, on the radar for panel testing. Fortunately, it’s starting to get there, obviously, but if you don’t have a trained medical laboratory professional on staff who can look under a microscope or conduct some type of test to rule out yeast -- you could have some slippage with respect to turnaround time on a diagnosis, so there’s a significant challenge.”
Kenters, et al. (2019) confirms that C. auris is a budding yeast that forms white, pink, or purple colonies on CHROMagar and can be difficult to distinguish from C. glabrata: “Some strains form aggregates of cells while others do not. In contrast to most other Candida species, it grows well at higher temperature (40-42° C) … First attempts to identify C. auris using PCR directly from swabs, seem to produce frequent ‘false positive’ results -- positive in PCR, negative in culture swabs. The first report of three cases of nosocomial fungemia due to C. auris showed that this yeast is commonly misidentified as C. haemulonii and Rhodotorula glutinis using traditional phenotypic methods. These widely used routine identification methods for yeasts are based on phenotypic assimilation/fermentation tests using sets of carbon and nitrogen compounds. An investigation of 102 clinical isolates, previously identified as C. haemulonii or C. famata, showed that 88.2 percent of the isolates were in fact C. auris, when confirmed by ITS sequencing. Several studies have since reported that, in routine microbiology laboratories, C. auris remains a problematic, difficult to identify pathogen, because commercial biochemical identification systems lacked this yeast in their databases.”
“C. auris transmission might be happening in a healthcare facility where professionals are completely unaware; they haven’t been able to detect it, or they are just missing it due to false negatives, and it begs the issue of the importance of having access to clinical microbiology services,” Rohde says. “An expert in clinical microbiology and medical laboratory needs to be part of this equation -- and not just for Candida auris, but for all pathogens in the healthcare setting.
Read further from the October 2019 issue HERE