Go easy on schools. It's central decision making that's tying their hands.

Ahhh time and money...

...night and day...
...hot and cold...
...prevention and IPC...
...BlueSky and X...

If only!

A little bit of background
We know that SARS-CoV-2 spreads in hospitals, and in other enclosed spaces.
We know you can find SARS-CoV-2 in the air and that airborne transmission occurs.
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Previous work in Addenbrooke's demonstrated that we could detect SARS-CoV-2 in the air of COVID wards (but not COVID ICU!) and that HEPA filters removed it very effectively
The key question, would this translate into reduced in-hospital transmission?
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So we set up the AAirDS study, deploying HEPA-based air cleaning units in two wards whilst not deploying them in matched wards – excluding periods when these wards were used as COVID-19 cohort wards themselves. Using routine healthcare data we then observed rates of COVID-19.

Overall COVID-19 was ‘lumpy’, and rates of in-hospital transmission were lower than expected but increased over time. Whilst the air cleaning intervention didn’t abolish transmission it was reduced by 22%

The hazard ratio for nosocomial transmission was 0.9 (95% 0.53-1.52) – so reduced, but we cannot be certain about this as the confidence interval crosses 1 (so true effect may be reduced transmission, no effect or even increased transmission)

In the second ward pair we saw a much smaller difference, but this was also as other restrictions were being lifted and compliance with the HEPA filters dropped as they were increasingly turned off.

Why did people turn them off? Multiple reasons, including not seeing these devices as important for infection prevention and control, being moderately noisy and perception of drafts. Whatever the reasons, inoperative devices won't have an effect.
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Given our previous findings of a wide range of other organisms in the air of hospitals, we also looked to see if other nosocomial infections (yellow bars in the figures above) were reduced – overall rates of these were too low to see any difference.

So what can we conclude. 1) The effect seen was consistent with previous data 2) If HEPA filters are effective they are far from a panacea 3) prevention of nosocomial viral infections will need a multi-modal approach.

We found for a few patients it was overly disruptive to sleep which likely then imprinted in staff to think it was bothersome for all hence why compliance gradually dropped.

Overall though patients found it less disruptive likely as for them it was constant whereas for staff it incr with proximity.

Good question. We didn’t specifically ask this, but these devices produce a low rumble which is mildly disruptive to conversation- but not a highly irritating high pitched whine.

On the noise aspects did you get any comments on the “quality” of the sound. Some noise is more annoying than others even though the dB can be the same.

This is likely to be something to do with the outcomes we recently reported. The HEPA filter intervention had a modest association with reduction in nosocomial COVID acquisition. Adherence to the intervention was imperfect, especially at later time points. t.co/ks5CpmHhtO