Page 49 - Green Builder May-June 2020 Issue

COVID-19:

Far More Infectious BY ERIN S. BROMAGE, PH.D.

Here’s science-based
Than You Think information about how easily

coronavirus spreads:

A COUGH: A single cough releases about 3,000 droplets and droplets
travel at 50 miles per hour. Most droplets are large and fall quickly,
thanks to gravity, but many do stay in the air and can travel across a
room in a few seconds.

A SNEEZE: A single sneeze releases about 30,000 droplets traveling at
up to 200 mph. Most droplets are small and travel great distances—
easily across a room.
If a person is infected, the droplets in a single cough or sneeze
may contain as many as 200 million virus particles which can all be
dispersed into the environment around them

A BREATH: A single breath releases 50 to 5,000 droplets. Most of these
droplets are low velocity and fall to the ground quickly. There are even
fewer droplets released through nose breathing. More importantly: Due
to the lack of exhalation force with a breath, viral particles from the
lower respiratory areas are not expelled.
Unlike sneezing and coughing, which release huge amounts of
viral material, the respiratory droplets released from breathing only
contain low levels of the virus. We don’t yet have a number for SARS-
CoV-2—the strain of coronavirus that causes COVID-19—but we can
use influenza as a guide. We know that a person infected with influenza
releases about 3-20 virus RNA copies per minute of breathing.

Remember the formula: Successful Infection = Exposure to Virus x Time

F A PERSON COUGHS OR SNEEZES, those 200 and take a few breaths, and you have potentially re- sis of contact tracing. Anyone you spend greater
million viral particles go everywhere. Some of ceived enough virus to establish an infection. With than 10 minutes with in a face-to-face situation
I the virus hangs in the air, some falls into sur- general breathing—in which roughly 20 copies per is potentially infected. Anyone who shares a space
faces, most falls to the ground. So, for example, if minute are released into the environment—things with you (say an office) for an extended period is
you are face-to-face with a person having a conver- are less severe, but you’re not in the clear. Even potentially infected. This is also why it is critical for
sation, and that person sneezes or coughs straight if every virus particle ended up in your lungs, you people who are symptomatic to stay home. Your
at you, it’s pretty easy to see how it is possible to would need 1,000 copies divided by 20 copies per sneezes and your coughs expel so much virus that
inhale 1,000 virus particles and become infected. minute = 50 minutes. you can infect a whole room of people.
But if that cough or sneeze was not directed Speaking increases the release of respiratory
at you, some infected droplets—the smallest of droplets about 10 fold; more or less 200 copies of Erin S. Bromage, Ph.D., is an Associate Professor of Biology
small—can hang in the air for a few minutes, filling virus per minute. Again, assuming every virus is in- at the University of Massachusetts Dartmouth. He
graduated from the School of Veterinary and Biomedical
every corner of a modest-sized room with infec- haled, it would take roughly five minutes of speak- Sciences James Cook University, Australia, where his
tious viral particles. All you have to do is enter that ing face-to-face to receive the required dose. research focused on the epidemiology of, and immunity
room within a few minutes of the cough/sneeze The Exposure to Virus x Time formula is the ba- to, infectious disease in animals.

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