The invisible menace! I’ve often thought it would be great if there was some visible sign that your hands had become contaminated during patient care. I guess that does happen to a degree when hands are visibly soiled – and we know that compliance with hand hygiene is almost universal when that happens. But what about when there’s no visible contamination but invisible and risky contamination with pathogens that can cause HCAI? A helpful systematic review and meta-analysis from 2019 suggests that around 5-10% of HCW working in acute care hospitals or care homes are contaminated with key hospital pathogens.

The review identified 57 studies that included data from studies that reported hand contamination rates with MRSA, VRE, C. difficile, A. baumannii or P. aeruginosa, and were conducted in acute care or care home settings. These rather broad inclusion criteria mean that the pooled estimated of contamination rates effectively represent a point-prevalence estimate of hand contamination at any given time. This is because a study where hands were sampled immediately after direct patient care for a patient with a known HCAI pathogen (with a high risk of contamination) would be included, but so too would a study where a HCW was met in a corridor and asked for a hand sample (with a lower risk of hand contamination) would also be included, with estimated pooled across all studies.

The pooled estimates for hand contamination rates by pathogen are shown in Figure 1. Overall, around 5% of HCW hands were contaminated with an HCAI pathogen, 9% for VRE, 6% for A. baumannii, 5% for P. aeruginosa, and 4% for MRSA. For C. difficile, only 4 studies were included, two of which drew a blank, one of which reported 10%, and the other 2%.

Figure 1: Pooled estimates of hand contamination rates with key hospital pathogens.

The more you think about this question, the more complicated it becomes. And the less useful the broad inclusion criteria selected for this study appear to be! The review reports contamination rate, which varies by organism, and by organism-region. However, there are some really fundamental variables that are not captured when looking at the data this way:

• Patient-level factors will influence greatly how many of these HCAI pathogens are shed into the environment, which will, in turn, influence hand contamination rates. For example, patients who are infected tend to shed more than patients who are colonised.
• Activity. The activity will be a big factor in determining contamination rate: is direct patient care involved? If so, what type and how long for?
• The timing of the sampling is crucial, especially in relation to hand hygiene. Were samples collected before or after hand hygiene? If after, how long after? Was that data even captured?
• Glove use will affect things too. Gloves are often used when caring for patients with HCAI pathogens – in fact, they are almost always used. Hand hygiene should be done after glove removal. But when were the cultures collected?
• How were hand cultures collected? Swab? Contact plate? Glove juice? These methodological issues will influence apparent prevalence.
• The background prevalence of HCAI on the ward will be important too. Is there an outbreak ongoing? How common are these HCAI pathogens in the setting where hands are being sampled?
• Environmental factors will play a part. When was the bed last made? Is the space adequate or cramped? Is the environment contaminated?

So, still lots of questions to answer in this area – and I wonder whether a more focused review that asked, for example “how frequently are HCW hands contaminated immediately after direct patient care but before hand hygiene for patients with key HCAI pathogens” may be more useful.