Grand Rounds Blog

There have been a lot of mixed messages during this pandemic.  First, we were told to be paranoid about cleaning surfaces – then later learned that this method of transmission didn’t matter quite as much.  Then we were told not to wear masks – but were later told that they were imperative.  Then there was emphasis on ventilation and doing events outdoors – but the latest super-spreader event in the Rose Garden was mainly held outdoors.  Given all this mixed messaging, many people – including parents, workers, employers, and school officials – are often left confused.

The fact is, this virus is only a few months old in human history.  We are learning something new almost every day – so keeping up can be difficult.  As a physician and epidemiologist, I try to help people sort through the constant changes to help them minimize their risks.  So here is a brief summary of what we know at the moment.

Based on the current scientific evidence, the novel coronavirus actually can spread in three different ways.

Droplets:  droplets are produced when people cough or sneeze — they are larger particles that don’t travel very far before they are pulled down by gravity (typically not more than 6 feet). If someone is next to you, and sneezes on you, the droplets can land on you and potentially enter your body (through your nose, mouth, eyes, etc). Physical distancing is key to preventing droplet spread, as are masks. So standing or sitting close to someone for prolonged periods of time, especially without a mask, can increase the opportunity for droplet spread.

Aerosols: There was a lot of back and forth in the scientific community about whether coronavirus spreads through aerosols.  A group of scientists demanded the World Health Organization acknowledge aerosols several months ago, and the CDC finally recently recognized aerosol transmission as well.  So what exactly are aerosols?  They are very small particles that are produced when a person talks or sings, and can travel far in poorly ventilated spaces (potentially much farther than 6 feet), because they don’t get pulled down by gravity as quickly as droplets. Aerosol transmission is what leads to many of the super-spreader events we keep hearing about, like the one with the church choir or the Maine wedding.  To reduce aerosol transmission, ventilation is key.  One study found that the odds of viral spread was almost twenty times less likely outdoors than in poorly-ventilated indoor spaces.  So outdoor settings, or open windows, or upgraded HVAC systems can reduce aerosol transmission. That said, if you are outside but fail to wear masks and get too close to others, droplet spread can still occur if someone sneezes on you.  So being outdoors alone is not enough.  Distancing and masks are still important.

Contact spread:  Contact transmission occurs when coming into contact with surfaces that have virus on it.  This appears to be the least common way the coronavirus is spread.  When people cough, sneeze, talk, or sing, the droplets or aerosols they produce eventually land on surfaces, like countertops and walls and floors.  This is where cleaning and disinfecting becomes important, along with hand washing and sanitizing.  And avoiding touching your eyes, mouth, or nose can help as well, in case your hands have some virus particles on them from touching a contaminated surface.


In order to effectively minimize risk of coronavirus spread, all three methods of transmission need to be addressed.  If you think of preventing spread as a math formula, it would be this:

Masks + Physical Distancing + Ventilation + Hygiene = Reduced Transmission


So holding an event outdoors but not wearing masks and being in close physical contact is not enough to reduce transmission.  Or maintaining 6 feet of physical distance and masks but being in a poorly ventilated environment may not be enough – especially if people take off their masks to eat.  (This is why eating outdoors, with more than 6 feet of distance between people, may be a better option than indoor eating).


Bottom line: This virus spreads by droplet, aerosol, and (less commonly) contact transmission – therefore, masks are better than no masks, outdoors is better than indoors, distancing matters wherever you are, and hygiene remains important. By combining all these preventive measures, you have the greatest likelihood of keeping people safe  – whether that’s at your business, your school, or the holiday event you are planning in your backyard.  


If you are having trouble weighing risks related to coronavirus, talking to a clinician can help. If you’re a member, please call us at 1-800-929-0926 or send us a message; we have virtual clinical guidance available to help support your needs during the pandemic. 

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