Something in the air?

Aerosols
Pic: Duncan C

A new paper in Clinical Infectious Diseases suggests that aerosols and the airborne/inhalation route could transmit Norovirus, demonstrating that Norovirus genomes could be detected in air samples inside and outside of rooms during outbreaks. The authors suggest that a healthcare worker could inhale up to 60 copies of virus during a 5-minute stay in a ‘symptomatic’ patient’s room. These particles, it is suggested, are available then to be swallowed.

So, given the fact that I still have some staff left in the hospital when Norovirus comes to call I’m thinking either this virus has a larger infectious dose than we think or the assumptions are not quite right. There was no linkage with the time lapse from the symptomatic ‘event’ apart from this was within 24 hr. of the sampling or with the type of event, or putting it bluntly, which end of the body the virus was ejected from the body from. Presumably the top end is a more effective disperser of viral particles than the lower end (depending on how sharply the sheets are pulled back..) and it would be interesting to see the effect of frequency of symptoms.

The authors suggest that this has implications for IPC, in that respirators/negative pressure rooms could be beneficial. I’d like to see a cost/benefit analysis of that one, especially as I’m not at all convinced that the use of PPE would actually reduce risk given how staff remove it so poorly. Closing a door, as they also suggest, would also be likely to be effective and somewhat cheaper. Given that attack rates for staff have dropped dramatically (in my experience anyway), my personal view is that improved hand hygiene, a recognition of the role of surfaces, reducing symptomatic patient movement and rapid isolation of the the affected have had most impact. If Norovirus were truly airborne with an inhalation route (especially given only short-term immunity) I suspect many individuals would be spending a considerable proportion of their time in an ‘indisposed’ state and the 5:2 diet and weightwatchers would be less popular.

To me, the real value of this research would be the development of a diagnostic tool that detects viable Norovirus particles from the air so that potential outbreaks could be prevented through early detection. Spotting ‘cases’ early when so many patients have a pretty good alternative rationale for their symptoms would be a real step forward for outbreak prevention and not attempting to bold stable doors after departure of the horse. Now that is something that would result in a sharp intake of breath.

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6 thoughts on “Something in the air?

  1. Thanks interesting review. The role of contaminated air in transmission (aside from airborne pathogens like measles) is where the role of contaminated surfaces was 10 years ago: if you sample air, you find a surprising amount of contamination. But is this cause or effect of transmission? And how do we configure studies to tease out the role of contaminated air aside from other routes?

    Who is going to do the randomised controlled clinical study of one of the various machines promising to reduce microbial contamination of the air?

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    • Yes. The other thing I’m thinking is the length of time pathogens may remain suspended in the air before settling. Is this why surfaces appear to be re contaminated after cleaning or is it sleeper cells within Biofilms? Would be interesting to see the effect of using a UVC room decontamination device on the air of an isolation room. Wondering if lots of activity during cleaning keeps particles suspended for longer meaning that they settle later. Would the use of UVC prevent this?

      I remember the old days when dressings were not done on the ward in the morning because of the level of activity, sheet shaking etc. No chance of leaving an isolation room to ‘settle’ before cleaning these days as there are normally so many people that could use it.

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  2. Great article. Personal experience of children in our household when sick with Norovirus is that I am on cleaning duty. 20 yrs of clinical microbiology lab work clearly marked me out as having required fortitude. I am scrupulous in cleaning and hygiene precautions in my duties. 50% of time have then successfully acquired Norovirus myself. I know it’s not my techniques as never got lab acquisition of gastrointestinal infection despite handling many faeces samples (we know the samples pots are pretty gross and request forms are often contaminated) definitely think I have acquired via aerosol route. Not foodbourne as wife who generally balks at required clean up operations gets off scott free! Again super post!

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