I started this post as I left a staff meeting today on containing the coronoavirus. We had a similar meeting 2 months ago and at that point I added that there was airborne transmission of the virus. The only comment I got was a condescending remark about how we don't know much about airborne transmission and we need to wait and see and blah, bah, blah. It was "as if" I did not know what I was talking about or any of the surrounding controversy. To my surprise the same people today were sold on airborne transmission. They were even interested in HVAC issues and negative pressure rooms – all of the stuff I have been studying for 20 years. Nobody mentioned UVC or air filtration. I decided just to keep my mouth shut. Just like I usually do when politics seems to be the priority rather than science. But the good news was undeniable. Airborne transmission has much greater acceptance than it did prior to the current pandemic and there are clear reasons for it.
That staff meeting is a small part of a larger landscape of
what airborne transmission advocates like me have been talking
about for decades or longer. Back in the
days when I was working in an outdated building that had an HVAC system that
was designed to contain heat rather than provide fresh air to dilute and remove
airborne pathogens – I routinely observed the effects of this approach on
myself and my coworkers. Upper
respiratory infections were endemic. If
one person came into that building with a severe form of a respiratory virus –
most people got it. I can recall coming down with an acute flu-like illness one
morning at work and getting ill so quickly and severely that I was barely able
to make it home due to the cognitive effects.
I was close to delirium.
When you are in medical facilities, the party line is
always “wash your hands”. I got the respiratory infections if I washed my hands
20 times a day or a hundred times a day.
The pandemic equivalent of that advice has been “don’t touch your
face”. But it is apparently safe to eat
food that has been contaminated with SARS-CoV-2 because the virus is not
infectious via gastrointestinal pathways. The expert opinion is really based on the lack
of evidence that eating food or touching food packaging is
associated with SARS-CoV-2 infections. We hear about the virus being infectious
through the eyes and nose. It could be rubbed into the eyes from the face or
into the nose by nose picking – but how common is that? Certainly, washing your hands and not
touching your face along with physical distancing at 6 feet seem like common
sense rules. But is that going to
protect you?
I have never felt like any of those measures was enough and
this week a
letter came out pointing out the evidence for airborne
transmission of respiratory viruses in general and for SARS-CoV-2 in
particular. I was pleased to see Dr.
Milton as a co-author of this statement.
I have been reading his work for 20 years on airborne viruses in
buildings of different design including the viruses that have been detected
both in the air and the occupants of the building. This paper is a brief
commentary specific to SARS-CoV-2 with a couple of generalities about airborne
viruses and it is signed by 239 scientists who support it.
The commentary starts out as an appeal to the medical
community to recognize the potential for airborne spread of COVID-19. Airborne transmission is defined as the
release of droplets containing viral particles during breathing, coughing,
sneezing, and any type of vocalization.
There is no doubt this happens. A distribution of droplet particle sizes
occurs. The larger droplets at a typical
velocity settle out of the air in shorter distances typically in about 2 meters
or 6 feet. The smaller droplets can travel much longer distances. The authors cite an example of a 5 µm droplet
at an original height of 1.5 meters and expelled at a typical indoor velocity
travelling for “tens of meters” before it falls to the floor. This is typical
airborne transmission and it will obviously not be contained by hand washing or
physical distancing.
The authors on to describe some of the well-known scenarios
where COVID-19 was transmitted despite no observed direct or indirect contact
among the parties where the transmission occurred by video recordings. They go on to cite other experiments demonstrating
that several viruses (influenza, Middle East Respiratory Syndrome coronavirus (MERS-CoV),
and respiratory syncytial virus (RSV) can all be spread by airborne routes. Although
they don’t go into a lot of technical detail in the commentary, respiratory
viruses are exhaled in normal tidal breathing.
The distribution and velocity of exhaled droplets will vary based on the
way they are generated. Infective viral
RNA in small (5 µm) droplets from COVID-19 has been detected.
The critical sentence from this document follows:
“Hand washing and social distancing are
appropriate, but in our view, insufficient to provide protection from virus
carrying respiratory microdroplets released into the air by infected people.”
The is really a landmark statement from this group of
experts. In my opinion it revolutionizes the approach not only to this virus
but all respiratory viruses. They
all have access to the same type of spread and many have already been shown to
have permeated heating and ventilation systems.
One of the main differences is virulence of the virus. For example, smallpox or variola virus can
cause an infection from the inhalation of a single viral particle (6). Adenovirus, a much more common respiratory virus
can cause an infection by the inhalation of as little as 6 viral particles (3). Although adenovirus is potentially a flu-like
respiratory virus, the main initiative at preventing the associated morbidity
and mortality occurs in the military where a vaccination is used. The SARS-CoV-2
infections dose has been estimated to be about 280 particles – but the authors
of one study suggest it is in the same ballpark of influenza virus and in that paper
suggest that the amount of virus leading to infection in volunteers may be
twice the amount of the aerosolized virus (5).
The main implication of airborne spread is that sustained
inhalation of COVID-19 in poorly ventilated spaces of just being indoors
increases risk of transmission. People who are coughing, sneezing, singing or engaged
in any activity that results in forceful exhalation will expel small droplets
at higher rates of speed and they will remain airborne for a longer period of
time and travel much greater distances than the current suggested social
distancing of 6 feet.
To reduce the airborne transmission risk they have straightforward
recommendations to avoid overcrowding (every additional person in the room is
generating airborne droplets), have adequate ventilation, and supplement these
measure with additions like HEPA filtration, germicidal UVC light, and exhausting
room air rather than recirculating it. I can recall getting into an argument at
one of my Avian Influenza Task Force meetings about a fast way to change the hospital
ventilation system in the event of an influx of avian influenza patients. Recall that the hospital was designed to retain
heat by recirculating room air rather than exhausting it – like modern hospital
rooms. At the time, the counterargument
was that it was just too expensive to build negative airflow rooms to
prevent the flu virus from leaving the room with medical staff caring for the patients. Most hospital rooms, even the ones I worked in
that were built in the 1960s, had windows to the outside. How difficult would it be to fit these windows
with exhaust fans to the exterior of the hospital?
This consideration is important now that there are political
initiatives to reopen schools and other public places. The ventilation systems of all of these
places should be looked at and that assessment incorporated into the overall
decision about how safe they are to open.
Further, there should be a systematic approach to how safe buildings are
in general from the perspective of transmission of respiratory viruses. A prospective approach that looks at how buildings in temperate climates need to be designed to minimize the spread of respiratory viruses needs to be a long term goal.
It took a virus with heightened mortality and morbidity to
raise awareness that physical measures rather than any available medication may
be the best way to contain respiratory viruses.
Airborne transmission of respiratory virus denial dies hard - but
hopefully it is being put to rest once and for all. That should be a continued priority for
everyone and momentum we cannot afford to lose.
George Dawson, MD, DFAPA
References:
1: Lidia Morawska,
Donald K Milton, It is Time to Address Airborne Transmission of COVID-19, Clinical
Infectious Diseases, , ciaa939, https://doi.org/10.1093/cid/ciaa939
2: Erin
Bromage. The Risks - Know Them - Avoid
Them. Erin Bromage COVID-19
Musings. May 16, 2020. Link
3: Yezli S, Otter JA. Minimum Infective Dose of
the Major Human Respiratory and Enteric Viruses Transmitted Through Food and
the Environment. Food Environ Virol. 2011;3(1):1–30. doi:
10.1007/s12560-011-9056-7. Epub 2011 Mar 16. PMCID: PMC7090536.
4: Nicas, M., Hubbard, A. E., Jones, R. M.,
& Reingold, A. L. (2004). The Infectious Dose of Variola (Smallpox) Virus.
Applied Biosafety, 9(3), 118–127. https://doi.org/10.1177/153567600400900302
5: Schröder I. COVID-19: A Risk Assessment
Perspective. J Chem Health Saf. 2020;acs.chas.0c00035. Published
2020 May 11. doi:10.1021/acs.chas.0c00035
Previous Airborne Transmission Posts from this Blog:
SARS-CoV-2 Is An Airborne Virus?
Viruses Are In The Air - Protection From Airborne Viruses
Hand Washing
New Twist On An Old Method To Kill The Flu Virus
Is It Time To Quarantine Air Travelers?
Supplementary:
This statement from a recent Nature article:
"But this conclusion is not popular with some experts because it goes against decades of thinking about respiratory infections. Since the 1930s, public-health researchers and officials have generally discounted the importance of aerosols — droplets less than 5 micrometres in diameter — in respiratory diseases such as influenza."
from: Dyani Lewis. Mounting evidence suggests coronavirus is airborne — but health advice has not caught up. Link.
Graphics Credit:
Graphic at the top is from Reference 1 based on the
following CC License. This
is an Open Access article distributed under the terms of the Creative Commons
Attribution- NonCommercial-NoDerivs licence
(http://creativecommons.org/licenses/by-nc-nd/4.0/),