CDC New NOTE on Covid-19

July 12, 2020

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

  1. Talking to someone face to face (with mask): Low risk if limit to less than 4 minutes
  2. Someone passing you by, like walking/jogging/cycling: Low risk
  3. Well-ventilated spaces, with distancing: Low risk (limit duration)
  4. Grocery shopping: Medium risk (can reduce to low by limiting time and following hygiene)
  5. Indoor spaces: HIGH RISK
  6. Public Bathrooms/Common areas: HIGH FOMITE/SURFACE TRANSFER RISK
  7. Restaurants: HIGH RISK (can be reduced to medium risk by surface touch awareness)
  8. Workplaces/Schools (even with social distancing): VERY HIGH RISK, including high fomite transfer risk
  9. Parties/Weddings: VERY HIGH RISK
  10. Business networking/conferences: VERY HIGH RISK
  11. Arenas/Concerts/Cinemas: VERY HIGH RISK

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.


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