From Marjorie McGuirk, Asheville, North Carolina, US
I tried to give my family a numeric guide to risk for coronavirus exposure to help them figure out which activities were riskier (24 October, p 40). It is my attempt to quantify exposure risk guidance from the US Centers for Disease Control and Prevention.
Give yourself a score for the following five factors. 1. Time – one point for every 15 minutes of exposure. 2. Mask – one point for a mask, two points for no mask. 3. Groups – one point if one to 10 people are present, plus an extra point for every further group of one to 10 people. 4. Breath rate – one point for talking, three for protests, five for running. 5. Location – one point for outside, two for inside at 2 metres apart. Finally, multiply the scores.
Example 1: you are talking outside with a friend for 15 minutes or less, with a mask, in a group of one to 10 people. This gives 1 × 1 × 1 × 1 × 1 = 1. Example 2: you are protesting for an hour outside with 100 people, half of whom are wearing masks, giving 4 × 1.5 × 10 × 3 × 1 = 180 points.
The lower your points, the lower your risk. I am a climatologist, so while I know a bit about probability and risk, I don’t know enough to understand the factors of covid-19, which is why I kept this to virus exposure only.
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