CDC has made officially the emerging scientific evidence on Coronavirus transmission:
Q: How does it spread?
1. Very low risk of transmission from surfaces.
2. Very low risk from outdoor activities.
3. Very HIGH risk from gatherings in enclosed spaces like offices, religious places, cinema halls, gyms or theatres.
Q: What does it take to infect?
To successfully infect a person, the virus needs a dose of 1000 virus particles (vp).
The typical environmental spread of activities:
1. Breath: ~20 vp/minute
2. Speaking: ~200 vp/minute
3. Cough: ~200 million vp (remain in air for hours in a poorly ventilated environment).
4. Sneeze: ~200 million vp (remain in air for hours in a poorly ventilated environment).
Q: What is the formula of successful infection?
Formula = (Exposure to Virus x Time)
1. Being in vicinity of someone (with 6 ft distancing): Low risk if limit to less than 45 minutes
The bottom line factors you can use to calculate your risk are:
- indoors vs outdoors
- narrow spaces vs large, ventilated spaces
- high people density vs low people density
- longer exposure vs brief exposure
The risks will be higher for former scenarios.