Dhe pathogen is relatively new and of concern to health authorities worldwide. The yeast fungus Candida auris, only discovered in 2009, has quickly spread internationally. From the start, the extremely stubborn pathogen was resistant to some antimycotics – drugs used to combat fungal infections – and some disinfectants.
The latest data from the USA now shows that the number of infections is increasing rapidly there, and the yeast is causing problems in more and more states. “These are considerable numbers of cases, and the fungus is not even widespread in all states,” says Oliver Kurzai from the University of Würzburg, head of the National Reference Center for Invasive Fungal Infections. “That’s worrying.”
The fungus does not usually attack healthy people – even if it colonizes them. But the pathogen should be kept as far away from hospitals and care facilities as possible – especially from intensive care units. Because if it gets into the body of people who are already ill or have a weakened immune system – for example via a catheter or breathing tube – it can become dangerous. The transmission takes place via smear infections, the pathogen does not spread through the air like the corona virus.
“Candida auris is a worldwide pathogenic yeast that can cause invasive candidiasis in the blood, heart, central nervous system, eyes, bones and internal organs,” wrote the World Health Organization (WHO) late last year in a call for the pathogen to be given top priority. The mortality from the disease, in which the fungus can attack internal organs, is between 29 and 53 percent.
In view of the problem, the US health authority CDC (Centers for Disease Control and Prevention) classified the fungus as an “urgent threat” in 2019 and introduced a reporting requirement.
Since then, the spread has accelerated, as a CDC study in the journal Annals of Internal Medicine shows. The fungus had already arrived in the USA in 2013, but was only discovered in 2016. That year, 53 clinical cases were registered, two years later – in 2018 – there were already 330. The cases rose to 476 by 2019 and to 756 by 2020. In 2021 the increase compared to the previous year was even 95 percent – de facto a doubling to 1471 cases.
The team speaks of a “dramatic increase”. In addition, more and more regions are affected – by the end of 2021, a total of 3270 clinical cases were registered in 28 of the 50 US states and in the capital Washington. Of the strains identified in 2020, 86 percent were resistant to azole antifungal agents, 26 percent of strains were unresponsive to the last-line antifungal amphotericin B, and some pathogens are even immune to all three classes of antifungal agents, the CDC said.
In Germany, the spread seems manageable so far: there have been around 40 clinical cases since 2015, says Kurzai. But the number is increasing here too, most recently there were 10 to 15 cases per year – so far without a fatal outcome. “We’re also seeing an increase here,” says the microbiologist. “We are observing this trend everywhere in Europe and also on other continents.” He cites South Africa, India, Brazil and the Arabian Peninsula as examples.
In 2021, an outbreak at the Berlin Charité ended mildly, where C. auris was transmitted between two patients in a Covid intensive care unit. As employees of the university hospital and Kurzai reported in the specialist journal “Mycoses”, a 65-year-old woman came to the ward and was immediately isolated because of the infection with a resistant bacterium – Klebsiella pneumoniae. Eleven days later, analyzes showed that she was carrying the yeast C. auris, which was not causing her any problems. But shortly thereafter, the pathogen caused sepsis in a 60-year-old man on the same ward.
Subsequent analyzes indicate that the patient was infected via an intubation spatula that had been used on the woman seven days earlier. Although the device had been disinfected, the chlorine dioxide used for it had not killed the stubborn pathogen. Disposable spatulas are now used on the ward.
Once the pathogen is in hospitals and care facilities, it becomes dangerous
“The situation was extremely dangerous,” says Kurzai. You were “lucky and worked very professionally at the Charité”. “Once the pathogen has arrived in hospitals, nursing homes and rehabilitation facilities, we have a big problem.” Although such a spread cannot be averted in the long term, “every year counts that we prevent it”.
In Europe, larger outbreaks in hospitals have now been reported from Spain, Italy and Greece – and repeatedly from England. In 2015/2016, 50 cases occurred in a cardiac surgery ward in a London hospital, 9 of which involved the bloodstream of humans. The outbreak dragged on for 16 months. And in an intensive care unit at Oxford University Hospital, an outbreak that affected 70 patients even lasted 2.5 years. The fungus was probably also transmitted by medical devices, such as probes to determine the temperature in the armpits – a body region that C. auris likes to colonize.
Kurzai justifies the fact that such outbreaks can drag on for a long time with the fact that the undemanding pathogen is not only difficult to eliminate in humans, but that it can sometimes survive on surfaces for months.
In order to be able to better monitor the development in Germany, Kurzai and other experts recommend reporting evidence of the fungus. In the specialist journal “Mycoses” they also recommend a whole bundle of measures, including screenings in clinics, hygiene rules and special disinfection strategies.
But where does the pathogen come from? Candida auris was first identified in 2009 in a 70-year-old Japanese woman in a Tokyo hospital. The Latin name “auris” comes from the fact that the fungus was found in the woman’s ear. Subsequent analyzes of stored samples found the earliest evidence of the pathogen to date in a blood sample taken from a small child in South Korea in 1996.
Experts are puzzled as to why various strains of the fungus appeared at relatively the same time in different regions of the world – South America, South Africa, South Asia and Japan. It is also amazing that a fungus that originally came from the environment could suddenly spread to humans.
That is absolutely unusual, says Bernhard Hube from the Leibniz Institute for Natural Product Research and Infection Biology in Jena. “Only 0.01 percent of the total of five million types of fungi can cause diseases in humans.” The fact that the fungus is easily transmitted between people is “an exception for fungi that could cause life-threatening infections,” emphasizes the expert.
In view of the high temperature tolerance – the fungus survives at up to 42 degrees Celsius – Arturo Casadevall from Johns Hopkins University in Baltimore suspects that climate change is involved. Only the adaptation to global warming enabled the species to colonize humans with their high body temperature of 37 degrees Celsius, wrote a team led by the microbiologist in 2021 in the journal “mBio”.
Another consideration is based on the fact that many C. auris strains are resistant to the azole antifungal group. At the same time, it is known that the large-scale use of antimycotics in agriculture promotes resistance to azoles in other pathogenic fungi. This raises the suspicion that the C. auris fungi found in humans also acquired their resistance through contact with these pesticides, as the WHO also writes. Both assumptions may sound plausible, but there is still no proof of this.
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