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By Dr. Gavin Macgregor-Skinner | July 29, 2020
As an epidemiologist or “disease detective,” a question I am frequently asked regarding SARS-CoV-2 (the virus that causes COVID-19 disease) is: “How does someone become infected?”
Everything we know about how this coronavirus behaves is based on data that has been collected in just a few months or has been hypothesized from the behavior of its relatives (SARS-CoV-1 from 2003 and MERS-CoV from 2012). How it spreads has generated significant debate. One reason for this is simply a lack of evidence.
SARS-CoV-2 virus transmission depends on the movement of people and spreads through close contact with a person who is infected with the virus. When an infected person coughs, talks, or breathes, they can release respiratory droplets that contain the virus. Other research has indicated that the virus may spread through indirect routes, such as by hands touching contaminated surfaces and then touching our eyes, nose, and mouth.
But understanding the mechanism of transmission is critical to ensure that the appropriate public health measures and workplace policies are implemented.
As Jonathan Kay stated in his article COVID-19 Superspreader Events in 28 Countries: Critical Patterns and Lessons:
If large respiratory droplets are found to be a dominant mode of transmission, then the expanded use of masks and social distancing is critical.
If small aerosol droplets are found to be a dominant mode of transmission, then we would need to prioritize the use of outdoor spaces, where aerosols are more quickly swept away, and improve the ventilation of indoor spaces.
If contaminated surfaces are found to be the dominant mode of transmission, then we would need to continue, and even expand, our current practice of washing hands as well as cleaning and disinfection protocols for high-touch surfaces to reduce the viral load.
What we do know is that before SARS-CoV-2 can spread to another person, it needs to be released into the environment from someone who is infected. Then, in order for someone else to get infected, they need to be exposed to an infectious dose of the virus.
How many SARS-CoV-2 virus particles are needed for an infectious dose is unknown. So how does an infected person spread a virus?....
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OPINION: Transmission through aerosols matters
By Linsey C. Marr
Ms. Marr is a professor of engineering.
Finally. The World Health Organization has now formally recognized that SARS-CoV-2, the virus that causes Covid-19, is airborne and that it can be carried by tiny aerosols.
As we cough and sneeze, talk or just breathe, we naturally release droplets (small particles of fluid) and aerosols (smaller particles of fluid) into the air. Yet until earlier this month, the W.H.O. — like the U.S. Centers for Disease Control and Prevention or Public Health England — had warned mostly about the transmission of the new coronavirus through direct contact and droplets released at close range.
The organization had cautioned against aerosols only in rare circumstances, such as after intubation and other medical procedures involving infected patients in hospitals.
After several months of pressure from scientists, on July 9, the W.H.O. changed its position — going from denial to grudging partial acceptance: “Further studies are needed to determine whether it is possible to detect viable SARS-CoV-2 in air samples from settings where no procedures that generate aerosols are performed and what role aerosols might play in transmission.”...
In a peer-reviewed study published in Nature on Wednesday, researchers at the University of Nebraska Medical Center found that aerosols collected in the hospital rooms of Covid-19 patients contained the coronavirus...
The Diamond Princess, a Case Study in Aerosol Transmission
A computer model of the cruise-ship outbreak found that the virus spread most readily in microscopic droplets light enough to linger in the air.
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In a year of endless viral outbreaks, the details of the Diamond Princess tragedy seem like ancient history. On Jan. 20, one infected passenger boarded the cruise ship; a month later, more than 700 of the 3,711 passengers and crew members had tested positive, with many falling seriously ill. The invader moved as swiftly and invisibly as the perpetrators on Agatha Christie’s Orient Express, leaving doctors and health officials with only fragmentary evidence to sift through.
Ever since, scientists have tried to pin down exactly how the coronavirus spread throughout the ship. And for good reason: The Diamond Princess’ outbreak remains perhaps the most valuable case study available of coronavirus transmission — an experiment-in-a-bottle, rich in data, as well as a dark warning for what was to come in much of the world.
Now, researchers are beginning to use macroscopic tools — computer models, which have revealed patterns in the virus’s global spread — to clarify the much smaller-scale questions that currently dominate public discussions of safety: How, exactly, does the virus move through a community, a building or a small group of people? Which modes of transmission should concern us most, and how might we stop them?
In a new report, a research team based at Harvard and the Illinois Institute of Technology has tried to tease out the ways in which the virus passed from person to person in the staterooms, corridors and common areas of the Diamond Princess. It found that the virus spread most readily in microscopic droplets that were light enough to float in the air, for several minutes or much longer.
The new findings add to an escalating debate among doctors, scientists and health officials about the primary routes of coronavirus transmission. Earlier this month, after pressure from more than 200 scientists, the World Health Organization acknowledged that the virus could linger in the air indoors, potentially causing new infections. Previously, it had emphasized only large droplets, as from coughing, and infected surfaces as the primary drivers of transmission. Many clinicians and epidemiologists continue to argue that these routes are central to disease progression.