" 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%. "
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.
This medium post provides a pretty good answer for this question: https://medium.com/swlh/so-youre-going-outside-a-physics-based-coronavirus-infection-risk-estimator-for-leaving-the-house-d7dcae2746c0
And see also the related calculator: https://sygo.mardillu.com/
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)
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.
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?"