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Visualizing How Covid-19 Spreads Indoors

posted by Jason Kottke   Oct 29, 2020

Visualization of how Covid-19 spreads in a bar via aerosols

From El Pais, this is an excellent visualization of how Covid-19 spreads indoors via aerosols and what can be done to limit that spread. They go through simulations of three different indoor scenarios that are based on actual events — in a home with friends, in a bar at 50% capacity, and in a classroom — and see what happens when differing levels of precautions are applied: masks, ventilation, and limiting exposure time.

Six people get together in a private home, one of whom is infected. Some 31% of coronavirus outbreaks recorded in Spain are caused by this kind of gathering, mainly between family and friends.

Irrespective of whether safe distances are maintained, if the six people spend four hours together talking loudly, without wearing a face mask in a room with no ventilation, five will become infected, according to the scientific model explained in the methodology.

If face masks are worn, four people are at risk of infection. Masks alone will not prevent infection if the exposure is prolonged.

The risk of infection drops to below one when the group uses face masks, shortens the length of the gathering by half and ventilates the space used.

In all three scenarios, note that distancing is largely irrelevant when people gather indoors for longer periods in poorly ventilated areas. From the school example:

In real outbreaks, it has been noted that any of the students could become infected irrespective of their proximity to the teacher as the aerosols are distributed randomly around the unventilated room.

The only thing that’s disappointing about this piece is that it does not stress enough that finding alternatives to indoor activities with lots of people is the much safer course of action than just cracking a window or masking up. Safety step #1 is still being smart about non-essential activities — masks and ventilation are not magically going to protect you during risky activities. Educating our children is important and difficult (though not impossible) to do outside in many places, so yeah, let’s mask up and ventilate those classrooms. But your indoor birthday party with 10 friends or Thanksgiving dinner with the cousins and grandparents? Or dining out in a room full of strangers at a restaurant? Even with masks and ventilation, it’s not a great idea. Scale it down, move it to Zoom/FT, hold it outdoors (distanced, masked), or just skip it.