Candida auris: why UV-C disinfection is part of the answer

A fungus that spreads like a bacterium

Candida auris was first described in 2009, and since then it has caused outbreaks in hospitals around the world. It can cause severe infections in patients who are already unwell, and many strains are resistant to more than one class of antifungal medicine.

What makes it especially difficult is how it spreads. Patients can carry it on their skin, and it contaminates surfaces and care equipment close to them. From there it can move to the next patient. Controlling an outbreak therefore depends heavily on how well rooms and equipment are cleaned.

Why chemicals alone are not always enough

Researchers at the US National Institute for Occupational Safety and Health (part of the CDC) point out that many chemical disinfectants commonly used in hospitals have shown variable results against C. auris. This is one reason health authorities have suggested UV-C as a possible addition to routine cleaning.

How much UV does it take?

The same NIOSH team exposed ten clinical isolates of C. auris to measured doses of UV light. C. auris needed significantly more UV energy to be inactivated than the more familiar Candida albicans. To reach a 99.999% reduction, the C. auris isolates needed between about 103 and 192 mJ/cm², compared with about 78 to 80 mJ/cm² for C. albicans. Different isolates also varied in how sensitive they were.

Time and distance decide the result

A 2019 study from the Netherlands and India tested a mobile UV-C device against C. auris strains from four regions. The best results came with a 30-minute exposure at 2 metres from the device. Halving the time reduced the effect about 10-fold, and doubling the distance to 4 metres reduced it about 50-fold. Strains from different countries also responded differently.

The practical lesson is that a UV cycle has to be long enough and close enough to deliver the dose the organism needs. In a typical patient room, that often means more than one position for the device, especially for surfaces far from it or hidden behind furniture.

What about far-UVC?

Research on far-UVC and C. auris specifically is still limited. Studies on related yeasts are encouraging: researchers at the Charité hospital in Berlin found that 222 nm light reduced colonies of Candida albicans and Candida parapsilosis by at least 98% at a dose of 40 mJ/cm². A Japanese study found 222 nm light worked well against C. albicans yeast, but was weaker than 254 nm against mould spores.

Putting it into practice

• Clean first. UV-C works best on surfaces that have already been cleaned of visible soil.
• Use a system that calculates the dose for the room rather than a fixed timer.
• Reposition the device where needed so distant and shadowed surfaces get enough exposure.
• Keep records of every cycle, so infection control teams can show what was done.