It’s two weeks into the First 2020 Lock Down. Life has been a riot of uncertainty and changed routines. I worked in laboratories for 16 years: three in a virology department, often working with radioactivity, and always with dangerous chemicals. In those early years I also had very young kids at home. And, I’ve been working as a chemical risk assessor for the last 20 years (considering and calculating exposure, and calculating risk from that exposure). I can’t think of any situation in the past where that professional experience has been of a practical use in real life. Until now. Now, having the mind-set that anywhere outside the home could be a source of virus contamination, and anything coming into the home could be a source of contamination, is useful.
We know some things in detail, but there are some uncertainties: but, the risk assessor knows this, and constantly revises the evaluation as information changes. The same applies here. When the Covid-19 emergency was confined to China, then no mitigation measures were necessary in the UK; once the virus had got into Europe and was obviously heading for the UK then the Government started implementing mitigation measures, as did many other organisations. Proportionate response to perceived risk. And, risk is different for different groups and different people. The epidemiological negative game changer is that for a large chunk of the population, symptoms are very mild or there are no symptoms, but the infected person is still a source of infection to others; this has only recently become apparent. But, then, all this is pretty recent.
This virus, a member of the corona virus family, is a bundle of RNA wrapped in protein and lipid (fat). The RNA part is particularly fragile, in that the world is awash with RNAses (enzymes that destroy RNA), which is one of the reasons why the lipid coat is important to the virus; but, fat is dissolved by detergents (and soaps) and organic solvents (e.g. alcohol). Hence, this virus is easily destroyed: but it is known (at this point in time) that the virus can persist on some surfaces for a number of days – at least one day on cardboard and at least three days on hard surfaces like plastic and steel. It will transfer from those surfaces to our hands if we touch them, and from our hands to our upper respiratory tract if we then touch our eyes, nose or mouth before washing our hands. It doesn’t, though, fly or jump. No contact, no transfer.
The virus gets to surfaces when infected people cough or sneeze (or exhale?), releasing viruses in their upper respiratory tract in very small water droplets. Hence, the 2 m minimum distance for social distancing – it is currently thought that beyond the 2 m the virus dose delivered is too small to be a concern (I’m not sure of this, yet). Hence the instruction to catch sneezes in tissues, and why wearing a suitable mask might now be useful (reduces chances of breathing in air sprayed virus, and reduces the chance that if the wearer is infected they deliver virus in droplets to their immediate environment), but not if you fiddle with the mask inappropriately when taking it off, or if it doesn’t fit properly in the first place.
So where are we now? The mitigation measure with the biggest positive effect, at the population level, is social distancing. This creates little hubs or nodes of populations (e.g. your family) that if infected can’t then spread the virus to lots of other isolated hubs. At the population level this is very disruptive to virus spread – no contact, no infection – and because the virus doesn’t persist long outside of the human host, this can result in the termination of the epidemic. We should all be implementing social distancing as carefully as we can. Long term, the most effective measure will be mass vaccination (assuming that this works for this virus) combined with effective treatment regimes. These measures will take a while yet to develop, in my opinion.
Social distancing is also the key mitigation measure at the household level; that is, keeping away from anyone else not part of the household. But, although much less risky than spending time in close proximity to non-household people, there are other potential sources of infection at the level of the household. Note that because the risk is small, and the resulting infection is retained in the isolated household, this is not a particularly important factor at the population level. It could be important at the household level, though. Anytime that members of the household leave the household there is a low risk that they will encounter sources of infection, and the magnitude of that risk will depend on the nature of the activity. The most important potential source of infection is other people – hence social distancing outside the home. The same applies to every time anything comes from outside the household into the household (e.g. deliveries, or food purchased from shops).
Putting the risk from non-household people aside (this is pretty easy to recognise, and fairly easy to mitigate the risk), the risk level associated with virus left on surfaces (which includes food packaging and food items) is currently unknown, but thought to be low. The risk increases as the epidemic deepens, because the number of infected people who are then sources of the virus also increases, and then decreases again as the epidemic lessens. But it is a risk that we can mitigate, because we understand it is there and we know what we can do to deal with it. Washing the surface with an appropriate cleaning medium removes the risk – no contact, no infection.
I particularly like the idea of wearing gloves (this can be household marigold gloves, or disposable gloves) when leaving the front door for any reason (including driving). This has two effects: it is a barrier between hands and sources of surface-borne infection, and it can be used as a means to train yourself not to touch your face with your hands (the thought here is that you fix in your mind that gloves equal risk – when working in laboratories I found that this built up an automatic association which resulted in me not touching my face if I was wearing gloves). The gloves are then removed before entering the house, and are either washed (if reusable) or disposed of, then hands are washed. I also wear gloves when unpacking deliveries, removing surface packing if feasible (straight to recycling or rubbish bin) and washing individual item packaging if possible. It’s also worth remembering that the other mitigation measure in this regards is time – leaving the item ‘socially distanced’ for a few days also significantly reduces the risks.
These secondary measures (after the primary social distancing measures) are currently of unknown importance, and definitely much less important than social distancing. But, no contact – no infection.