Candida auris: What is the deadly fungus sweeping through US hospitals?

The drug-resistant fungus Candida auris (C. auris) was only discovered some 15 years ago but is already one of the world's most feared hospital microbes.

If it gets inside the body, the yeast-type fungus can affect the bloodstream, the nervous system and several internal organs. The World Health Organization (WHO) estimates that its mortality rate ranges from 30% to 53% of patients affected by an invasive infection.

What is more worrisome is that the fungus has proven to be resistant to the most common types of antifungal drugs. Some strains are resistant to all of the medicines we have, says BBC's health correspondent James Gallagher.

According to the US Centers for Disease Control and Prevention (CDC), there have been outbreaks in more than 30 countries. A 2020 review from case reports from those nations found almost 4,750 cases globally between 2009 and 2019.

The CDC said new data showed the fungus has "spread at an alarming rate in US healthcare facilities" in 2020 and 2021. Clinical cases in the country trebled - from 476 in 2019 to 1,471 in 2021.

Also, a 2019 study by an international team of researchers suggested that rising temperatures linked to climate change may have played a role in the rising number of Candida auris infections.

Here is everything you need to know about this deadly superbug.

Candida auris (C. auris) is a yeast, a family of fungus which contains species pretty helpful to humans in activities such as bread-making and beer-brewing, but which also features species that cause infections in humans.

One example is the very common Candida albicans, which causes thrush but also may trigger more severe infections.

C. auris was first discovered in the ear canal of a patient at the Tokyo Metropolitan Geriatric Hospital in 2009, which inspired its name (auris is Latin for ear).

Most of the time, Candida yeasts live on our skin without causing problems, but they can cause infections if we are unwell or they get into the wrong place, like the bloodstream or the lungs.

C. auris most frequently causes bloodstream infections, but it can also affect the respiratory system, the central nervous system and internal organs, as well as the skin.

These infections are usually quite serious.

The fungus is often resistant to the usual drugs, which makes infections difficult to treat.

"The biggest problem with this fungus is its resistance to the drugs we have," said Dr Tina Joshi, associate professor in Molecular Biology at the University of Plymouth, in the UK.

"But another issue is that identifying a C. auris infection is quite difficult and it can easily be mistaken for other fungi, leading to the wrong treatment."

This means that the patient might be ill for longer, or get worse before accessing the appropriate treatment.

Transmission is mainly through contaminated surfaces in hospitals. It sticks to intravenous lines and blood pressure cuffs. It's really hard to clean off, according to Dr Neil Stone, leading fungal expert at the Hospital for Tropical Diseases, University College London.

The solution is often to close off entire wards.

"It is the most worrying fungi and we ignore it at our peril," Dr Stone said.

"It could shut down entire healthcare systems."

In a statement issued on 20 March, the CDC said new data showed that the fungus has "spread at an alarming rate" in the US.

It is unlikely that you will pick up a C. auris infection going about your daily life.

However, the risk is higher if you are in a hospital for a long time or if you are in a nursing home, and patients who are in intensive care are much more likely to get a C. auris infection, according to the CDC.

The risk of picking up an infection is also higher if you have been on antibiotics a lot, because the drugs also destroy good bacteria that can stop C. auris getting in.

Resistance to the common antifungal drugs, like fluconazole, has been seen in the majority of C. auris strains.

This means that these drugs do not work on C. auris. Because of this, less common antifungal drugs have been used to treat infections, but C. auris has now developed resistance to these, too.

DNA evidence shows that the antifungal resistance genes in C. auris are very similar to those found in the very common C. albicans.

This suggests that the resistance genes may have passed from one species to the other.

A 2019 study, published by the journal mBio from the American Society for Microbiology, suggested that the reason C. auris infections have become so common may be because this species has been forced to live at higher temperatures because of climate change.

Most fungi prefer the cooler temperatures found in soil. But, as global temperatures have risen, C. auris has been forced to adapt to higher temperatures.

This may have made it easier for the fungus to thrive in the human body, which is warm at 36C to 37C.

A better understanding of who is most at risk of contracting a C. auris infection is the first step towards reducing the number of infections.

"We are behind the curve in what concerns the study of fungi," Dr Joshi said.

"I am not surprised at all we are now having to catch-up with it."

Healthcare professionals need to know that people who spend long periods of time in hospitals or nursing homes or those who have a weakened immune system are at higher risk.

Not all hospitals identify C. auris in the same way. They are sometimes mistaken for other fungal infections, like thrush, and the wrong treatment is given.

Improving diagnosis will help to identify patients with C. auris earlier, which will mean that the right treatment is given - preventing the spread of infection to other patients.

But above all, infection prevention efforts need to be improved, said Dr Joshi.

"The main measure is infection prevention and control, because we have already seen how difficult it is to tackle what it does to patients."

"Hospitals need to be on top of disinfecting and cleaning."

Not quite. In its first-ever list of fungal "priority pathogens", published last October, the WHO named no less than 19 fungi that represent a great threat to public health.

C. auris was one of four fungi to appear in the "critical priority" group, being described by the WHO as "intrinsically resistant to most available antifungal medicines".

This article has been adapted from material produced by Lena Ciric and James Gallagher.