Do we need a hand to accurately identify C. auris carriage?

Candidozyma auris has emerged as one of the most consequential fungal pathogens in modern healthcare, distinguished by its ability to spread efficiently, resist disinfection, and persist on skin and environmental surfaces.
I really enjoyed listening to Dr Areej Al-Ali's webinar on C. auris last week (you can watch back the recording if you missed it here). Areej referenced a paper which is mainly about C. auris environmental contamination. But in the detail of the paper, there's a fascinating detail about C. auris colonisation patterns that I thought was worth highlighting. It seems that patient hand contamination may be a vital and often overlooked reservoir for colonisation!

This recent multicenter study from Illinois and California in the USA provides some striking evidence to suggest that patient hands, and especially palms and fingertips, are crucial sites for C. auris colonisation and subsequent environmental contamination and wider dissmenation. 41 patients known to be colonised with C. auris were sampled at five body sites: axilla, inguinal crease, nares, palms and fingertips, and perianal skin. And guess which single site was the most effective at detecting colonised patients? Yep, it was the palms and fingertips, which would have detected 76% of colonised patients if it was the only site used to sample. This surprised me!

So, what's going on here? Why are the hands so frequently colonised in this study?

• Skin shedding: Hands constantly shed skin squames, an efficient vehicle for C. auris dispersal.
• Environmental contact: Hands interact with high-touch surfaces more than any body site.
• Moisture and microbial ecology: The palmar surface creates microenvironments conducive to yeast persistence.
• A key question raised by these findings is whether the hands are actually 'colonised' (i.e. C. auris has taken up residence in the microbiome!) or transiently 'contaminated' - or perhaps somewhere in between!

Given that hands are the primary interface between patients, healthcare workers, and the environment, colonization at this site has disproportionately high transmission potential. In fact, it seems likely that patient hands are the main reason for the other key finding of this study: that the inanimate environment became rapidly decontaminated (after 4 hours!) following disinfection. Also, whilst not evaluated in this study, a very high proportion (93%) of these patients were co-colonised with other MDROs - so could it be that hand contamination is equally common with other MDROs?

Before we jump to generalised conclusions though, as ever, there are limitations to consider:

• The sample size was fairly small at 41 patients.
• The patients were sampled from settings with a very high risk of MDRO colonisation (as illustrated by the finding that 93% of the patients were co-colonised with more than one MDRO).
• There was a limited range of settings included.
• The study did not include direct observation of practice for patients or staff.
• The study relied on culture-based detection, which does not provide the complete picture of colonisation.
• There was no longitudinal follow-up; the study was undertaken over a short timeframe.

Notwithstanding these limitations, the study suggests that hands could be an important body site for colonisation to include in patient sampling strategies. The latest UK guidance for detecting C. auris colonisation recommend screening the the axilla, groin and nose, plus consideration of 11 additional sites if clinically indicated...none of which include the hands! CDC guidance is more straightforward, recommending sampling the axilla and groin...again, with no mention of the hands.

So, are we missing a trick in not including patient hand sampling for the detection of C. auris and possibly other MDRO colonisation?