In late March 2023, the U.S. Centers for Disease Control and Prevention highlighted the threat posed by a rapidly spreading fungus called Candida auris that is causing infections and deaths among hospital patients across the country. The unexpected rise of this recently discovered pathogen is part of a larger trend of increasing fungal infections in the U.S.

Arif R. Sarwari is a physician and professor of infectious diseases at West Virginia University. Amid rising concerns among doctors and public health officials, Sarwari helped explain what Candida auris is, how it is spreading and how worried people in the U.S. should be.

1. What is Candida auris?

Candida auris is a recently identified, single-cell fungus that can infect humans and is moderately resistant to existing antifungal drugs. You might be familiar with superficial fungal infections – like athlete’s foot or vaginal yeast infections – which are quite common and don’t pose significant risks to most people. In contrast, Candida auris and other related fungi can cause infections within a person’s body and are much more dangerous.

Candida auris is a type of yeast that was first identified in 2009 and is one of a number of species in the candida family that can infect people. In the past, most invasive candida infections were caused by Candida albicans. Recently, though, infections with species of candida that are much more resistant to drugs than Candida albicans – like Candida auris – have shot up, with a nearly fivefold increase since 2019.

2. How dangerous are candida infections?

For the most part, healthy people do not have to worry about invasive candida infections. There are two groups of people who are most at risk for dangerous candida infections: first are patients in intensive care units who also have central intravenous catheters and are receiving broad spectrum antibiotics. Patients with weak immune systems, such as cancer patients on chemotherapy or patients with human immunodeficiency virus, are also at high risk of candida infection.

Nearly all people have candida fungi growing in their guts and on their skin as part of their microbiome. When a person is healthy, candida numbers are low, but the fungi can proliferate rapidly and overcome a person’s immune system when a patient is sick and on antibiotics.

If candida cells on a person’s skin contaminate an intravenous line, the fungus can get into a patient’s bloodstream and cause often deadly bloodstream infections. Candida species are the fourth most-common cause of hospital associated bloodstream infections.

There are three classes of antifungal drugs that can be used to fight invasive candida infections. Candida albicans is susceptible to all three and easier to treat than Candida auris, which is moderately resistant to all three classes of antifungals.

3. How common are invasive fungal infections?

The CDC estimates that in the U.S., around 25,000 patients get candida bloodstream infections every year.

Candida bloodstream infections are best understood as a tale of two eras. In the past, they were almost always caused by drug-susceptible Candida albicans that arose endogenously from a patient’s own microbiome. There was no concern about infections spreading to other patients.

The recent emergence of drug-resistant and more transmissible Candida auris is raising alarms among health professionals. Because this species can contaminate surfaces and easily spread from patient to patient, the fungus is causing outbreaks both within and between hospitals.

4. Why are fungal infections increasing?

Fungal infections have been rising in the U.S. in recent years, especially infections caused by Candida auris. The pathogen only caused a few infections each year between 2013 and 2016, but starting in 2017, infections began to rise rapidly with 2,377 confirmed cases recorded in 2022 according to the CDC. Deaths caused by all candida infections are rising, too, from 1,010 in 2018 to nearly 1,800 in 2021.

The reasons for this increase are complicated, but I think there are two main drivers: more, sicker patients in hospitals and a stressed health system, both of which got worse during the COVID-19 pandemic.

Hospitals are seeing more very sick patients with weak immune systems, especially as the population ages. This means there are more susceptible patients at hospitals to begin with.

Additionally, any time the health system is stressed – like during a pandemic – drug-resistant bacterial and fungal infections increase. This is because very sick patients are usually in crowded wards and exposed to many antibiotics. In addition, loss of hospital staff and increased workload results in lower quality sanitation - causing more spread of resistant pathogens.

I view the rise of drug-resistant fungi like Candida auris through the same lens as worsening antibiotic resistance. The more antibiotics people use, the greater the chances a resistant strain will become dominant.

5. What can the medical community do about it?

There are a few options for fighting the rise of drug-resistant Candida auris.

The most effective measures are good infection control practices. These behaviors and protocols include practicing good hand hygiene before and after each patient contact, wearing isolation gowns and gloves that are carefully discarded in a patient’s room, and taking measures to detect Candida auris infections early and isolate patients to prevent the spread. Though relatively simple, these actions are key to preventing the spread of all antibiotic-resistant pathogens, not just fungi.

The second option is to develop better drugs to treat new, antifungal-resistant strains of candida. Many new antifungal drugs are already under development. However, prevention through sound infection control will always remain foundational, as further drug development is akin to an arms race.

Arif R. Sarwari does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.