[ Parent Question — Coronavirus: Justified Practical Advice Thread ]

If I interact with someone with nCov for an hour, how likely am I to get nCov?

by Raemon1 min read1st Mar 20208 comments

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I'm guessing data is limited here, but a related-related question might be "how likely am I to catch the flu or a few other common diseases by interacting with a victim for an hour?"

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" In Sichuan province, 25,493 contact persons were named, 25,347 (99%) were found, 23,178 have already been examined and 0.9% of them were infected. In the province of Guangdong, 9,939 contacts were named, all found, 7,765 are already examined and 4.8% of them were infected. That means: If you have direct personal contact with an infected person, the probability of infection is between 1% and 5%. "

https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-report.pdf?fbclid=IwAR1r1hTkCcLUPPeXvYXpDkZ4XsuAvUdH1JQFbfE9LztHs0VIH7o3bY6GlWs

That's not particularly useful without the base rate of infection in those provinces, and it appears to at least double count (assuming 'close contact' is a reciprocal relationship, every case of two people in close contact both being infected would count as two cases of a close contact being infected).

Based on the upper estimate of 2.5 for R_0, those numbers suggest that the average person has fewer than 50 'close contacts', and likely even fewer.

Answer depends on several things

1. Where you met, temperature, humidity, degree of ventilation

2. Distance and intensity of interaction and exchange of fomites

3. Degree of infectivity (were they coughing and their viral shedding; where they are in illness course)

4. Hygiene, theirs and yours, including hygienic behaviors

5. Your level of immunity (are you already immune, are you immunocompromised, etc)

Do you have a sense on how it depends on any of those things?

1avicennah2yTransmission risk 1. Goes up with humidity and down with more ventilation and warmer temperatures 2. Higher with smaller distances and fomites Infectivity 3. Increases with greater viral inoculate (which goes up with more shedding), which is also greater with 4. reduced hygiene and direct contact with mucous membranes. Even at smaller inoculates, 5. an immune incompetent host has higher chances of infection. Happy to provide citations for anything you’re specifically curious about.
2Raemon2yThanks. The thing I'm ultimately looking for though is more like "at humidity X, your likelihood is Y". I know roughly how the variables fit together, but not enough to decide "do I let a random person who might have covid into my house or not?"
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I'm hoping that we've gained more information about this in the past month. If anyone is able to assemble the current bits of evidence we have bearing on this (either from Covid itself, or similar illnesses), I'd still super appreciate it.