Yeast of burden

Five things to know about Candida auris.

An emerging species of Candida unlike any other is insidiously infecting hospitalized patients across the world.

Candida auris was first described in 2009, after it was isolated from a patient's external ear discharge in Japan (hence the species name). But the yeast causes more than just ear infections. In particular, candidemia is of paramount concern, with reported mortality rates as high as 60%, based on data from a limited number of patients, according to the CDC.

Photo courtesy of the CDC
Photo courtesy of the CDC

Beyond its reputation for high mortality, C. auris is also often resistant to multiple antifungal drugs, the CDC reported last November. To make matters worse, the species is difficult to both identify and eradicate, said Jose A. Vazquez, MD, FACP, a professor of medicine and chief of the division of infectious diseases at the Medical College of Georgia at Augusta University. “It's like one great perfect storm to really be able to have this organism be transmitted all over the world,” he said.

In the U.S., the first known case of C. auris was discovered in 2013, and as of Feb. 16, 35 cases have been reported in five states. The overwhelming majority of cases (28) were reported in New York, three were reported in Illinois, two were reported in New Jersey, and one case each had been reported in Maryland and Massachusetts, according to the CDC. C. auris infections have also occurred in South America, Asia, Europe, and Africa.

Experts offered five key points that hospitalists should know about this evolving health threat.

1. Unlike other Candida species, C. auris is difficult to eradicate from the hospital environment.

C. auris does not seem to be acting like a typical, commensal Candida, said Tom Chiller, MD, MPHTM, chief of the CDC's Mycotic Diseases Branch. Instead, it's behaving more like a nosocomial bacteria (e.g., Acinetobacter species, carbapenem-resistant Enterobacteriaceae) that sticks to surfaces and spreads from surface to patient, health care worker to patient, or patient to patient, he said. “Normally, [hospitalists] would see a Candida, and they're not going to be worried about contact precautions [or] spread to other patients in the same room,” Dr. Chiller said.

However, clinicians must take a novel approach with this strange new pathogen. “We need to take slightly different actions here and treat it more like a transmissible bacteria that they're used to dealing with, take precautions in infection control, and work with your micro[biology] lab to try to get a Candida species identified that is unidentifiable,” Dr. Chiller said.

At least in the U.S., C. auris appears to be a hospital phenomenon, and the CDC is not yet as worried about the yeast spreading in the community, he added. It has caused outbreaks in health care facilities, and one of the largest to date occurred in a thoracic ICU at a London hospital specializing in cardiothoracic surgery. From April 2015 to July 2016, 50 cases of C. auris colonization were identified, with a 44% observed rate of infection and an 18% rate of candidemia, according to a study published last October in Antimicrobial Resistance & Infection Control. The study authors noted that C. auris carriage was negligible in the admitted population and that no deaths were directly attributable to the related infections.

Moreover, the study highlights the yeast's persistent presence around bed spaces, equipment monitors, and other fomites. This demonstrates just how resilient and difficult to eradicate C. auris can be, even in a sophisticated ICU, said Cornelius J. Clancy, MD, an associate professor of medicine and director of the mycology program at the University of Pittsburgh School of Medicine. “To me, probably the greatest threat that this presents is that if it ends up getting into hospitals—even hospitals that have robust infection control measures—from what we know to this point, it can be a very, very tough thing to control,” he said.

2. C. auris has shown resistance to all three major classes of antifungals.

The yeast species has demonstrated the ability to become multidrug resistant, Dr. Chiller said. “We have found some of these isolates to be—not in the U.S. yet—resistant to all three classes. That's concerning,” he said. In cases of such broad resistance, multiple antifungal classes at high doses may be required to treat an infection, according to the CDC.

“This is the very first time that we have ever even considered having a yeast that is multidrug resistant,” said Dr. Vazquez, a Candida researcher who participated in creating the CDC's interim recommendations last November (see sidebar). He drew comparisons with the rapid global spread of multidrug-resistant bacteria, such as those that produce Klebsiella pneumoniae carbapenemase or extended spectrum beta-lactamase. “A couple of isolates in New York and a couple of isolates in London and Paris and, lo and behold, five or six years later, it's all over the world,” Dr. Vazquez said.

To this point, most C. auris isolates that have been described throughout the world have been resistant to fluconazole, and amphotericin B resistance rates appear to be in the 30% to 50% range, Dr. Clancy said. With resistance rates around 10% in the studies reported thus far, echinocandins appear to be the most viable treatment in the antifungal armamentarium, he said.

3. The most vulnerable patients are often the sickest.

Based on limited data, risk factors for C. auris infection seem to be similar to those for other types of Candida infections (e.g., recent surgery, diabetes, broad-spectrum antibiotic and antifungal use, and central venous catheter use), according to the CDC. Infections have affected patients of all ages and have most frequently occurred in patients hospitalized for other reasons, according to the agency.

The first few C. auris infections in the U.S. have occurred in very sick, medically compromised patients who have been in and out of health care facilities and received procedures and central lines, Dr. Chiller said. “It is being found in the sickest of the sick, which doesn't surprise me for a new organism that is trying to figure out its niche and is, thankfully, just being barely introduced in this country,” he said. So far, U.S. cases seem to be very localized. “I think that's good. I think we're early in this emergence, and now is the time to act and to really try to contain as best we can,” Dr. Chiller said.

4. Infection with C. auris may have higher mortality rates than other strains of Candida.

Despite aforementioned mortality rates hovering around 60%, it's unclear whether patients with invasive C. auris infection are any more likely to die than those infected with other Candida species, Dr. Chiller said. “Mortality with patients in these populations that are very sick in ICUs is always a challenge to attribute to one thing. . . . We need more data to understand the true attributable mortality,” he said.

Dr. Clancy said he believes that as more cases of C. auris get reported, the 60% figure will likely be the upper limit of mortality for severe bloodstream infections. “My guess is that overall mortality is going to be comparable to what we see with Candida bloodstream infections due to Candida albicans or other species that we already encounter, which are already pretty high—usually in the range of about 40% overall,” he said.

5. Most hospital laboratories won't be able to correctly identify C. auris.

C. auris is not readily identified by biochemical techniques or by the machines used in hospitals to identify organisms, Dr. Chiller said. Most hospitals test bloodstream isolates down to the species level, but C. auris frequently masquerades as other Candida species, said Dr. Clancy, who is also chief of the infectious diseases section at the Veterans Affairs Pittsburgh Health Care System. “I think the key thing for hospitalists, and for all providers, at this stage of the game is to understand how your lab is doing testing, how it's identifying Candida species, and if it has methods that would detect C. auris or not,” he said.

Labs that are equipped to correctly identify the yeast employ matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry testing with a library that contains C. auris sequences or direct DNA sequencing, Dr. Clancy said. More commonly used conventional methods get it wrong. For example, the API 20C system might misidentify C. auris as Rhodotorula glutinis, the VITEK 2 method could pick up C. haemulonii, and the MicroScan method could produce various results (e.g., C. famata), he said.

If any of these unusual yeast species are detected in the blood or if a patient is not responding to conventional antifungal therapy, clinicians may consider submitting the isolate to the CDC to see if C. auris is the culprit, said Dr. Vazquez. “I would say 99% of institutions have no way of knowing they even have a C. auris infection,” he said.