EDITOR'S NOTE: Barbara Turpin is Chair and Professor, Gillings School of Global Public Health, UNC-Chapel Hill. She is past-president and Fellow of the American Association for Aerosol Research. A more detailed version of this essay is available here. Over the last week, we have watched COVID-19 spread in the White House and take hold in the Senate. This is a good time for an update on how to stay safe. The most effective interventions involve actions taken by infected people before they know they are infected. No one wants to give a deadly disease to their employees, coworkers, friends, or even their political rivals, and people are most contagious before they know they have COVID-19. So, to keep from spreading the disease, we must act at all times like we might already have it.
When each of us talks, coughs, sneezes, and especially when we sing, we create a plume of
airborne particles (aerosols and droplets) that extends several feet in front of us. When someone is infected with COVID-19, these particles contain the coronavirus. We know the virus is present in
respiratory fluid, and it has been measured in
aerosols from infected patients.
Imagine President Trump, practicing for the debate with Chris Christie and talking constantly. If one of them was unknowingly already infected with COVID-19, the worst place for them to be would be facing each other just across the table - in the high concentration plume. Staying more than 6 feet apart, outside of the plume of exhaled particles, dramatically reduces exposure.
When someone wears a mask, the speed of their expelled particles causes most particles to hit the mask and be removed. Even a simple cloth mask can reduce the emissions of aerosols by the wearer by about
70%.
When everyone wears a mask, each person’s exposure is reduced by about 80%. Masks may have prevented transmission during Amy Coney Barrett’s Oval Office reception.
What happens to that plume of particles? When we cough or sneeze, some droplets are very large, about 100 microns in diameter. They fall in under one minute and within several feet. You could be exposed by standing so close they hit you in the face (yuck) or by touching a contaminated surface and then one’s face. But there is another way.
You could be exposed just by being in the same room as an infected person, if you stay long enough. The majority of particles (aerosols) emitted when vocalizing are smaller than one micron. Instead of falling, they mix rapidly throughout the room. Thus, when people stay 6 feet apart, they breath much lower concentrations, but are exposed to more viruses the longer they spend in the room.
To illustrate, had he stayed 6-feet away, Christie’s potential exposure during an 8-hour debate practice would have been 100 times greater than his exposure at the 40-minute Oval Office reception for Barrett, assuming similar ventilation.
Be thoughtful. Keep your distance. Wear a mask. Minimize time indoors where people are not masked. Stay at home if sick and isolate if exposed.
