C. auris: A Bad Bug With a Worst-Case Scenario
Three pan-resistant isolates detected in the United States
Imagine if a common healthcare-associated infection became impossible to treat.
The nightmare scenario public health officials are contemplating is that an emerging strain of multidrug-resistant Candida auris will displace treatable strains of Candida, which are already a leading cause of bloodstream infections.
C. auris has shown this ability in other countries, becoming endemic in some healthcare systems and occasionally generating strains that are completely resistant to all antifungals.
“Clearly, the pan-resistant part of this is what we are worried about,” said Tom Chiller, MD, MPHTM, chief of the mycotic diseases branch at the Centers for Disease Control and Prevention (CDC). “And I think what keeps us up at night is C. auris leapfrogging over other Candida species and becoming a major cause of candidemia that also can acquire resistance and become really hard to treat.”
Chiller updated the threat of the emerging fungus at the IDWeek 2019 conference, held Oct. 2-6, 2019, in Washington, DC.
There have been three pan-resistant isolates of C. auris confirmed in the United States. Other isolates impervious to all three classes of antifungals have been reported in at least four other countries on several continents globally. The U.S. isolates were already resistant to fluconazole and amphotericin B, then developed resistance to echinocandin while under treatment with the drug.
“They developed echinocandin resistance while on echinocandin, which is concerning,” Chiller said. “All of these cases were unrelated, and we didn’t see any transmission.”
Fortunately, C. auris resistance to echinocandin remains relatively rare, he said.
From May 2013 — when the first C. auris was identified in the United States — to July 2019, there have been about 800 clinical infections and 2,350 colonized patients. New York, “ground zero” for this emerging pathogen, as Chiller termed it, had 388 clinical cases as of Aug. 31, 2019.
Illinois had 227 cases, followed by New Jersey with 137 and Florida with 24. Nine other states reported a range of C. auris clinical cases from one to eight.
As prevalence increases, so does the concern that C. auris will become a leading source of fungal infections. Outbreaks in India and Spain showed C. auris displacing other Candida strains like C. albicans and C. parapsilosis, he said.
“Also, in South Africa, the second most common cause of candidemia is C. auris,” he said. “This thing can get into a system and take over — and these are invasive infections.”
Again, candidemia has been a leading cause of bloodstream infections for years, but the source is often the patient’s gut microbiome, which is disrupted during invasive medical care.
“That is different in this Candida auris,” Chiller said. “This is really a paradigm shift from what we have thought of as Candida infections. This is a yeast that is acting like a bacteria. Resistance is the norm. It thrives on skin and contaminates patient rooms — not your GI tract. It is transmitted in healthcare settings because of this [contamination].”
In particular, C. auris is spreading in skilled nursing facilities for ventilated patients (vSNFs), and long-term acute care hospitals (LTACHs), he said. Indeed, a study1 presented at IDWeek 2018 revealed that Chicago healthcare facilities are struggling to contain C. auris, primarily because it has established reservoirs in these step-down sites. (See Hospital Infection Control & Prevention, January 2019.)
“How is it spreading in these settings? One hypothesis we are looking into is the idea of a ‘super shedder,’” Chiller said. “In other words, patients are shedding skin cells with C. auris on them by the millions in their rooms. That’s how it is spreading and contaminating surfaces.”
For example, CDC experiments thus far have shown a strong correlation between C. auris on patients’ skin and environmental contamination on their bed rails.
“We find a ton of C. auris on bed rails when we do sampling,” he said.
Compounding the problem, C. auris can remain viable in the environment for up to a month, requiring strong disinfectants to eradicate. There are three cleaning products now with EPA claims for efficacy against C. auris. Sporicidals used for C. diff also will kill the bug, but quaternary ammonia compounds are not effective, he said. In addition to environmental cleaning, the threat of C. auris warrants vigilance with hand hygiene and contact isolation precautions for infected or colonized patients, Chiller emphasized.
“Once it sets up shop it tends to begin to spread in facilities from patient to patient,” Chiller said. “We have seen this [pattern] across the globe as well. In the [United States], these patients are usually the sickest of the sick.”
They may be on mechanical ventilation, have tracheotomies, are often colonized with other resistant pathogens, and may have a recent history of receiving antibiotics and antifungals.
Testing, Decolonization Woes
Complicating detection and control measures, rapid C. auris tests are not currently available in most hospitals but are in use in the seven regional sites that comprise the CDC’s Antibiotic Resistance Laboratory Network (ARLN). The CDC is working on testing protocols for colonization, but C. auris can be as difficult to detect as it is to treat or decolonize. For example, C. auris can evade lab detection without specialized equipment, as standard clinical testing may misidentify the pathogen with more benign Candida strains like C. haemulonii, the CDC reports.2
The CDC is concerned that C. auris will become widely dispersed nationally, similar to what happened with carbapenem-resistant Enterobacteriaceae (CRE). “There are institutions [in endemic areas] who are screening everyone [that] comes into a hospital so that they know whether to put them into contact isolation,” Chiller said. “We are trying to take a very aggressive stance. I don’t think we were as aggressive with CRE, for example, and now we know CRE is everywhere.”
There have been cases where a C. auris patient was identified and promptly isolated, the environment was cleaned rigorously, and no subsequent transmission occurred.
“That’s our strategy, but we need a better, quicker screening test in hospitals so that they can do it on site,” he said. “That is obviously one of our limitations. And of course, how to decolonize someone — we really don’t know how to do that.”
Some have tried chlorhexidine bathing, with mixed results, he said.
“These patients seem to be colonized indefinitely,” Chiller said. “We have patients document now as being colonized for years — not just months. They can be intermittently positive — so we are saying if you are ever positive on the skin you are colonized [and must be in contact isolation].”
This is reminiscent of the phrase “isolation for life” infection preventionists have applied to other multidrug-resistant pathogens.
“For this organism, the environment is really the major problem,” Chiller said. “I don’t think there is a lot of person-to-person transmission. I think it is person-to-environment, then environment back to person. This sucker is hard to clean and hard to kill.”
- Kerins J, Kemble S. Rapid emergence of Candida auris in the Chicago region. Abstract 923. IDWeek 2018. San Francisco. Oct. 3-7, 2018.
- CDC. Candida auris information for laboratory staff. Available at: https://bit.ly/2rZKn3s. Accessed Dec. 9, 2019.
Imagine if a common healthcare-associated infection became impossible to treat. The nightmare scenario public health officials are contemplating is that an emerging strain of multidrug-resistant Candida auris will displace treatable strains of Candida, which are already a leading cause of bloodstream infections.
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