On March 20, 2023, several media outlets and viral social media accounts promoted a story about, as the Daily Mail reported, a "highly contagious fungus with a kill rate of 60% ... spreading through the US." The phrases "kill rate of 60%" combined with the phrase "highly contagious" became central pieces of doomsday tweets or reporting about the fungus:
The fungus, Candida auris, was first discovered in Japan in 2009, and has been of concern to the U.S. Centers for Disease Control and Prevention (CDC) since 2016, when the first seven U.S. cases were described. The concerns centered around its resistance to common anti-fungal medicine and its prevalence in health care settings:
Data from these cases suggest that transmission of C. auris might have occurred in U.S. health care facilities and demonstrate the need for attention to infection control measures to control the spread of this pathogen.
As a result, the CDC's Mycotic Diseases Branch has been tracking the number of C. auris cases in the United States over time "to assess the impact of prevention strategies and inform public health practices." Since 2018, health care facilities have been able to report cases of the fungal infection directly to the CDC.
The impetus for a new batch of headlines surrounding C. auris was a new review of that surveillance data published by CDC researchers in the journal Annals of Internal Medicine. This study reported on a "dramatic increase" in C. auris cases since 2019:
A total of 3270 clinical cases and 7413 screening cases of C auris were reported in the United States through 31 December 2021. The percentage increase in clinical cases grew each year, from a 44% increase in 2019 to a 95% increase in 2021. … From 2019 to 2021, 17 states identified their first C auris case. The number of C auris cases that were resistant to echinocandins in 2021 was about 3 times that in each of the previous 2 years.
A news release for the study described C. auris as "highly contagious." Building off that news hook, other headline-generating assertions regarding C. auris in media reports come from either a 2020 review paper or from data presented on the CDC website. The latter website states that "30–60% of people with C. auris infections have died." These statements are alarming, but they are even more alarming without key context.
'Kill Rate of 60%'
The apparently high mortality rate from C. auris is, in large part, an artifact of the population from which positive cases of C. auris were identified: elderly hospital or long-term care inpatients who, as the CDC wrote, "had other serious illnesses that also increased their risk of death." In the United States, according to a 2019 study, nearly all documented cases stem from this population:
Most patients with C. auris infection in the United States have had extensive exposure to healthcare in the months preceding the C. auris infection, particularly in higher acuity long-term care facilities, such as long-term acute care hospitals and skilled nursing facilities that support patients who are chronically ventilator dependent.
Meghan Lyman, the lead author of the 2023 study, described this problem to The New York Times:
Dr. Meghan Lyman … said that the [CDC] did not have a good sense of how many deaths to attribute directly to the fungus. The reason is that people who become infected are also dealing with multiple other health challenges, so C. auris can be both a cause of death or something that, along with other poor-health factors, hastens it.
While the new release for this study described C. auris as "highly contagious," it is unclear how contagious it is in healthy people or outside of a hospital setting. The lack of knowledge could be related to the fact that sampling and testing is performed only in a hospital setting, but it could also indicate that infections generally come from contaminated hospital equipment, as described in the aforementioned 2020 review:
C. auris invasive infection and colonization have been identified almost exclusively in patients in high-dependency areas with the highest degree of medical intervention. Although transmission of C. auris in healthcare settings has been well documented, less is known about transmission in the community … [M]uch more data are needed to understand the ecological niche of this species and community-based studies are necessary to understand the risk of transmission outside healthcare settings.
Within the hospital setting, there is evidence that healthcare workers can transfer the fungus from one patient to another, that infected patients shed the fungus, and that it can survive on a variety of surfaces for extended periods, as described in the 2020 review:
Environmental sampling for C. auris has found the organism in several places in rooms of patients and hallways outside patient rooms, including beds, chairs, windowsills, countertops, trolleys, electrocardiogram leads, blood pressure monitoring cuffs, infusion pumps, and ventilators.
Shared and mobile equipment, like temperature probes, have also tested positive for C. auris and provide a potential transmission route for patients placed in single rooms. To make matters worse, C. auris persists on surfaces. In laboratory studies, C. auris has been shown to survive on moist surfaces for at least 7 days, on dry linen for up to 7 days,11 on dry steel disks for at least 7 days, and on dry plastic coupons for at least 14 days.
In healthy individuals outside of intensive health-care facilities, however, the risk of acquiring an infection and dying from it are substantially lower. "C. auris is not a particular threat to young healthy people, whose immune systems can fight it off," The New York Times reported. "Those who contract it can experience typical infection symptoms, like fever and chills that can intensify absent treatment."
The Bottom Line
C. auris is indeed a significant threat and is therefore in need of monitoring and scientific research. C. auris is increasingly resistant to a first-line, anti-fungal treatment and almost fully resistant to another. It persists in humans with compromised immune systems, and is hard to eradicate or even detect in the very healthcare settings in which these individuals are often found.
C. auris, then, is a threat to the ability of the global healthcare system to protect patients from hospital-acquired infections. However, the fungus does not yet appear to be highly contagious outside of a hospital setting, and a reported mortality rate of 60% is based on limited data collected largely if not only from already sick patients.