How dirty is your QWERTY?

I was recently involved in a study to examine the microbial profile of computer keyboards in a multi-centre study in the UK. The findings have just been published in the Journal of Hospital Infection

Keyboards were collected from staff clinical areas (e.g. “nursing stations”) in a hospital and dental practice in Scotland, and hospitals in Wales and England. The keyboards were taken from a range of wards and other clinical areas to try to get an overview of contamination. The aim of the study was to focus on dry surface biofilm rather than live plantonic bacteria, so the keyboards were washed with sterile water prior to testing. Keys were selected a random for swab testing. For the swab test, keys were swabbed and plated onto various agar plates. Keys were then incubated in TSB broth overnight as an enrichment culture before being plated onto various agar plates. There’s a couple of nice protocol details here worth mentioning – keys of a similar English language frequency were selected to try to control for the amount of contact they have had and hence contamination risk. Also, the pressure of swabbing was controlled to meet the match the average force of a finger whilst typing (0.7 to 1.7 N if you’re interested). (Mrs Otter would argue that my “angry” typing style is at least 2N.)

52 keys from 13 keyboards were tested. Interesting, none of the initial swab tests grew any bacteria, whereas following enrichment culture, a high proportion of key yielded potential pathogens. Amazingly, MRSA was cultured from 72% of keys, VRE from 31% of keys, and MDR Acinetobacter from 17% of keys (Figure). Given the surprisingly high proportion of MRSA identified on these keyboards, we went back and double checked that the lab methods were suitable for distinguishing MRSA from other meticillin-resistant bacteria, and were satisfied that they were.

Figure: Percentage of keys which resulted in bacterial grown on MacConkey agar, multi-drug-resistant (MDR) Acinetobacter spp., vancomycin-resistant enterococci (VRE) and meticillin-resistant Staphylococcus aureus (MRSA)-selective plates. Blue bars = Welsh hospital; yellow bars = Scottish hospital; grey bars = English hospital; purple bars = Scottish dental practice.

A serial transfer experiment was also undertaken, finding that viable bacteria were able to be transferred from 9/13 keys tested following wiping with sterile water, and 7/13 keys following wiping with a chlorine-containing disinfectant.

The findings highlight the potential risk that contaminated keyboards may pose in clinical settings. Whilst swabbing of the keyboard keys following washing did not yield any viable bacteria, enrichment culture identified a range of important hospital pathogens. Furthermore, the keyboard keys were able to transfer bacteria between multiple surfaces even after cleaning or disinfection. It seems likely that dry surface biofilm is the culprit here, making the case for different strategies to address dry surface biofilm specifically.

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