By Betsy Todd, MPH, RN, nurse epidemiologist and AJN clinical editor. Published: March 20.
As we have become a little more comfortable with the concept of social distancing as a way to mitigate the spread of this new coronavirus, a new worry seemed to dominate conversations this week: the idea that the virus can linger in the air. The takeaway for many people, at least in the conversations I’ve been having, is that you can become infected by simply walking down the street. There is no evidence that this is true (unless, of course, someone sneezes in your face!).
Results of recent experiment deepen our understanding.
A March 17 research letter published in the New England Journal of Medicine reported on experiments in which SARS-CoV-2, the virus that causes COVID-19, was artificially aerosolized. (For comparisons, SARS-CoV-1, which causes SARS, was also aerosolized.) A nebulizer was used to aerosolize the virus, and the aerosol was fed into a rotating drum. The drum apparatus helps to keep the suspended aerosols from settling out of the air, so that their dynamics can be more closely studied.
Under these controlled conditions, the researchers were able to demonstrate that artificially aerosolized virus remained viable and infectious for three hours, and that therefore it’s “plausible” that, if something causes the virus to aerosolize outside of the lab, this could be another mode of transmission for COVID-19.
The researchers didn’t claim that coughing or sneezing causes the virus to aerosolize, nor that aerosolized virus under less controlled conditions (that is, without the aid of a rotating drum) can remain suspended in air for three hours. And yet some media reports seem to have left people with the impression that SARS-CoV-2 aerosols are floating around in the air. There is no evidence so far to support this.
Medical procedures that may cause virus aerosolization.
However, since at least the SARS outbreak in the early 2000s, we have assumed that respiratory viruses might aerosolize under certain conditions, such as during intubation or tracheal suctioning in hospitalized patients. CDC guidance for the care of patients with COVID-19 therefore recommends that N95 respirators be worn by staff present during these procedures. But the lack of evidence that the virus aerosolizes in any other situation is one reason why the CDC tells us that surgical (“droplet”) masks can be worn during the routine care of people with COVID-19 infection.
So what did we learn from this study?
This new study demonstrated that SARS-CoV-2 can remain infectious for hours in an aerosol (under very specific laboratory conditions), and also added to our knowledge of why the epidemiology of SARS was so different from what we’re seeing with COVID-19, in spite of the fact that the two are closely related coronaviruses. The study authors point to some possible reasons for this:
“We found that the stability of SARS-CoV-2 was similar to that of SARS-CoV-1 under the experimental circumstances tested. This indicates that differences in the epidemiologic characteristics of these viruses probably arise from other factors, including high viral loads in the upper respiratory tract and the potential for persons infected with SARS-CoV-2 to shed and transmit the virus while asymptomatic.”
What the research didn’t say.
But the researchers never claimed to have demonstrated that COVID-19 is now being spread by the airborne route.
There are still many unknowns about COVID-19, and much more to learn. But at this time, based on this research as well as on what we learn from tracking COVID-19 spread from person to person, neighborhood to neighborhood, and region to region, there doesn’t seem to be evidence of airborne transmission events.
Transmission of COVID-19 via droplets, or indirectly by contact with contaminated surfaces, remains the focus of infection control efforts as COVID-19 spreads.
Spreads by close contact. Spreads from Asymptomatic people. Are Hospitals & clinics consistent in response to threat? Some mandated Temp checks for all staff – some did not? Masking of all staff was needed months ago. Social distancing of staff was needed months ago. How many healthcare workers came to work with their own PPE and were told not to wear it? How many healthcare workers have been in crowded meeting areas where no staff had faces covered? Are healthcare workers and patients informed when they have been exposed to a Covid + staff members or patient? It is not HIPPA violation to say, “You have been exposed.” Is contact reporting or tracing occurring? Is exposed staff sent home to quarantine for 2 weeks? How many Nurses and Healthcare care workers have been exposed at facilities became sick and were denied testing. Where is OSHA in all of this? How can healthcare workers with serious injury from Covid 19 file for worker’s compensation if they have not been tested? Do facilities handle other occupational exposures in this manner… TB, Needle sticks…
A brief note from post author Betsy Todd in response to comments: I absolutely agree – health care professionals should be overprotected and not underprotected. The exposure of nurses with direct patient contact is far more intimate and longer in duration than anything that most people in this country have to deal with, and in case this virus aerosolizes even rarely, caregivers need to be fully protected. My concern is that the results of this study are being interpreted by the general public as “the virus is airborne.” Some people are afraid to walk outside. Most people don’t understand the difference between a health care worker’s exposure to the virus (intense), and therefore caregivers’ greater need for protection, and their own actual risk. They also don’t understand what nurses know well – that droplet and contact transmission can be very efficient, especially in a situation in which asymptomatic infected people may be significant contributors to droplet and contact spread.
I fear that some people won’t bother with frequent hand de-germing and awareness of contaminated surfaces because they assume the virus is airborne. But from what we’re learning, early directives remain true: keeping our hands clean and away from our faces (to prevent touch contamination), and maintaining social distancing (to prevent droplet contamination), are our best protections against the virus.
“There doesn’t seem to be evidence of airborne transmission”. Well, when there actually IS NO EVIDENCE of airborne transmission, then I think healthcare workers at the frontlines will worry a little less. The CDC has lost much credibility by their ridiculous recommendations based not on evidence-based research, but by “last resort” measures.
“The researchers didn’t claim that coughing or sneezing causes the virus to aerosolize”. Really? Do researchers need to claim this? Coughing, sneezing, exhaling – all create aerosols! https://www.nejm.org/doi/full/10.1056/NEJMicm072576
https://web.archive.org/web/20071014074854/http://www.sgm.ac.uk/pubs/micro_today/pdf/110503.pdf
Could we be “over-doing” it with unnecessary wearing of N95s? I honestly think it’s too soon to tell and I would much rather be over-protected than under protected. Yes, I am a nurse on the front lines caring for these COVID positive and rule out patients. I don’t want to be bring this to my loved ones at home. Yes, I am a nurse and I love my job, but there are thousands of nurses out there. My kids have only one mother.
Wouldn’t it be safer to assume it could become airborne?