Risk

A risk management approach? I have a few issues with Jason’s thinking here.

There is a vast difference between making a public health recommendation and informing personal risk assessments. The Vice article is forlornly wandering between the two viewpoints trying to make them homogeneous.

“What it’s suggesting could be accurate and useful, but we have no way of knowing that at the moment.” [1]
We have no way of knowing? We do have multiple pieces of information from several studies. We can use that in our risk assessment modelling, and adjust our behaviour accordingly. This is how Plan > Do > Review works. You update your assessment as new information becomes available.

i.) Social Distancing
We know that the 1.5m distancing is most likely insufficient for running and cycling – being behind someone releasing a snot rocket makes this pretty obvious.
An individual making a risk assessment for their outdoor activity will be using Dynamic Risk Assessment, or an OODA Loop, to be safer.
The paper reaffirms the issue with the 1.5m during running and cycling;

❝ This suggests that avoiding substantial droplet exposure in the conditions of this study can be achieved by one of two actions: either by avoiding to walk or run in the slipstream of the leading person or by keeping larger social distances, where the distances increase with the walking or running speed. The equivalent social distance for walking and running in the slipstream is defined as the distance that should be kept between the leading and trailing walker/runner to avoid substantial exposure to slipstream droplets, similar to the case where two people are standing still at 1.5 m distance. ❞ [2]

The published literature for masks during the last weeks have been clear that physical distancing is currently the key social engineering measure; depending on the location this distance is either 1.5m, 6ft, or 2m (already we have variance).

❝ Finally, WHO continues to emphasize the utmost importance of frequent hand hygiene, respiratory etiquette, and environmental cleaning and disinfection, as well as the importance of maintaining physical distances and avoidance of close, unprotected contact with people with fever or respiratory symptoms. ❞ [3]

“there currently is no consensus about how dangerous it is to exercise or be outside” [1]
There is a currently undefined risk, this risk may/can be mitigated using physical distancing. The Medium write up [4], quoting the study [2] gives some estimated distance which are greater than the distances for standing/walking.

❝ On the basis of these results the scientist advises that for walking the distance of people moving in the same direction in 1 line should be at least 4–5 meter, for running and slow biking it should be 10 meters and for hard biking at least 20 meters. Also, when passing someone it is advised to already be in different lane at a considerable distance e.g. 20 meters for biking. ❞ [4]

🏃‍♂️ —-10—- 🏃‍♂️ running

🚴‍♂️ —-10—- 🚴‍♂️ slow ride

🚴‍♂️ ———20——— 🚴‍♂️ fast ride

ii.) Aerosol Transmission
A study published in the New England Journal of Medicine in mid-March said aerosol transmission was “plausible”; so aerosol transmission has not been eliminated as a vector.

❝ Our results indicate that aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days (depending on the inoculum shed). ❞ [5]

“Where the droplets are is much less relevant than the amount of transmission that occurs via this route” [1]
The epidemiologists viewing a population are going to have a different view on this than the individual.
The epidemiologist will probably also be a binary thinking mode.
The aerodynamics is outside of an area that the epidemiologist should be commenting on.
The individual is considering the risk to themselves, and if they can avoid that risk.
Is the study enough for a CMO to make a public health recommendation? Of course not – but it should definitely prompt some further questions in this area.
Is it enough for an individual to use in their risk assessment – absolutely!

“Hanage said it’s probably OK to exercise outside as long as you “apply common sense.” ” [1]
Common sense; like having a greater physical distance when performing activities such as running and cycling?

iii.) Risk
We know aerosol transmission is “plausible”.
We know social distance is important for limited spread.
We know there is a high probability of aerosol in the 1.5m to 2.0m social distancing space.
We know there is less probability of aerosol in the increased distances when running and cycling.

A simple risk calculation for Covid-19 when running and cycling in the 1.5-2.0m social distance; Exposure = occasionally (3), Likelihood = likely (0.6) and Consequence = Major (10). This produces a risk estimate that is HIGH risk, and the easiest way to mitigate the risk is to use these larger distances when participating in the activities.

For some the Consequence = Catastrophic (20) and that would be your figure for some age brackets or for comorbidity pushing the risk up to EXTREME, where the increased distance become even more important.

“What it’s suggesting could be accurate and useful, but we have no way of knowing that at the moment.” [1]
Is the information useful? Absolutely, and if further study gives us more optimised distances we will use them in our risk assessment.

REFERENCES:
[1] The Viral ‘Study’ About Runners Spreading Coronavirus Is Not Actually a Study (2020-Apr-10) [VICE]
[2] Towards aerodynamically equivalent COVID-19 1.5 m social distancing for walking and running (preprint) [Urban Physics and Wind Engineering]
[3] Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations (2020-Mar-29) [WHO]
[4] (2020-Apr-08) [Medium]
[5] Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1 (2020-Mar-17) [New England Journal of Medicine]

( This post was initially a Twitter thread. )