Stay Indoors - But Is That Enough?

 

Any casual reader of this blog might know that I was interested in indoor air quality including airborne viruses – long before it became fashionable. That had various origins including an undergrad focus on ecology, being raised by two heavy smokers, having to manage a coal fired stoker as a kid, working in a HEPA filtered clean room as a research assistant, and routinely getting viral respiratory infections in a hospital staff setting where we were all advised that hand washing was supposed to stop the mini-epidemics. And having asthma through all of that.

The indoor air quality issue has become complicated as our outdoor environment deteriorates. As an undergrad 50 years ago, we studied air pollution scenarios that affected large cities.  That included the concept of how smog was created by photochemical reactions but a lot of the specifics were not known.  More recently the entire Midwest and Northeastern US has been blanketed by wildfire smoke from Canada. Wildfire smoke is chemically complex.  In a lot of areas there are air quality alerts on one day due to wildfire smoke and ozone the next day. Those alerts are graduated to advise people with health conditions like asthma, emphysema, and heart disease on the lower end to limit outdoor activities or stay inside.  At high levels everyone gets the same advice.

The advice to stay inside assumes that your indoor air quality is better than the outdoor air quality that you are being warned about.  But is that a valid assumption?  How do you get measurements on everything and know the critical differences?  A good place to start is the outdoor air quality. The EPA has developed a nationwide network of sensors that detects particulates and ozone in the air and calculates the air quality index.  The AirNow app is available for your smart phone.  It gives you the outdoor reading, particulates, and ozone, as well as the break points from Good (0-50) to Hazardous (301-500). It will give you conservative advice about what to do about health and activity for those break points.

The CDC has a publication on indoor air quality in airports (1) where smoking was allowed. It provides some more intuitive markers of indoor quality. They found that the PM 2.5 (<2.5 micron particles per cubic meter) were 300+ in the smoking areas and 50+ in the areas adjacent to the smoking areas.  300+ levels are considered “very unhealthy”.  Anyone who has ever been in a smoke-filled room can probably sense that the atmosphere is not very good for your health either immediately of after leaving.  In Minnesota when the AQI was greater than 300 due to wildfire smoke – you could smell the wood fired smoke.

With an accurate assessment of the outdoor air – what about your indoor air quality?  I was fortunate enough to have purchased an air cleaner for my office with a PM 2.5 measure built into the machine. It usually reads in the 1-5 range but when the wildfire smoke arrived it was suddenly reading 40+ indoors. I had to figure out why that number was so high.  I had just replaced my furnace and it has a MERV13 filter that should provide some filtering efficiency.  The question mark was how my air exchanger fit into the mix.

My house is about 15 years old and like most modern houses it is considered airtight.  The concern by builders and contractors with modern homes is that they are so airtight that it leads to indoor air pollution from a number of sources including any combustion processes in the home and volatile compounds in the air from various sources like cleaning products.  As a result, air exchangers are installed to vent the indoor air and bring in fresh outdoor air.  These air exchangers are designed to reduce heat exchange and most do not have HEPA ( High Efficiency Particulate Air [filter])  filters.  They have a relatively primitive filtration system to remove mainly insects and very large particles. They can easily bring in outdoor smoke so it is a good idea to have it shut off on days where there is very high particulate matter.

The problem with my new system is that I was not sure that the air exchanger was off.  When my new furnace was installed the air exchanger was integrated into a touch panel with 30 different options and several ventilation settings.  I talked with 5 technicians (3 from the HVAC contractor, 1 from the air exchanger manufacturer, 1 from the smart thermostat manufacturer).  They all agreed shut off the air exchanger was a good idea but they gave me widely varying advice.  I decided to experiment myself over a period of 12 hours and generated the following graph (click to enlarge).

The first section shows the AQI outdoors versus indoors running the MERV 13 filter through the furnace.  There is no difference over that time period.  The next period I shut off the furnace filter and used a free-standing Space Gaard air cleaner with a MERV 8 (MERV = Minimum Efficiency Reporting Values) filter. Notice that during this time period the wind picked up outdoors, blew off some smoke and the PM 2.5 dropped from 160 to about 90.  At that time I talked with a 6^th technician and he gave me clear advice on how to shut off the air exchanger.  The last section is with the air exchanger off and all air circulating through the furnace filter MERV 13.  At that point the indoor AQ drops consistently despite a blip upwards in the outdoor PM 2.5 and continued to drop to 10.  To me that illustrates the importance of making sure the air exchanger if off when the outdoor AQ is poor and actively managing it to turn it one when the outdoor AQ is acceptable.

A related indoor AQ related to viral transmission is the carbon dioxide CO₂ levels.  Lower levels correlate with less people rebreathing air in the room and that decreases the risk of infection from airborne viruses. Outdoor CO₂ is roughly 400-420 ppm. My indoor measure is currently 570 without the air exchanger on.

There are currently PM 2.5 and CO₂ monitors available in most home stores and large online retailers.  What we really need is a more comprehensive single device that measures and records all of the parameters. I would suggest PM 2.5, PM 10, CO₂, Ozone, and Volatile Organic Compounds (VOC).  The closest I could come to that device was a gadget that required that I purchase a separate weather station and even then the bandwidth to multiple devices was limited.

Home HVAC system design could also use some innovation. Just based on my experience durability is a problem. Should an HVAC system last longer than 14 years?  Probably.  But the design itself does not seem very efficient.  I am not a certified HVAC tech by any means but it appears to me that the air exchanger introduces outdoor air into the system after the air filter so that any particulate matter in the outdoor air does not get at least one pass through the highest efficiency filter.

Outdoor air quality is a little discussed casualty of climate change. As the environment deteriorates, I expect that there will be increasing amounts of wildfire smoke and it will be chemically more complex. I currently wear an N95 mask outdoors during the alerts, but I can envision a time in the not-too-distant future where respirators that can also remove ozone and organic chemicals will also be necessary. Geography is no longer helpful in separating clean air from polluted air. Monitoring your personal indoor air quality and figuring out how to manage it will become the most critical part of home management. I have posted a few things that you can do right now and I am always interested in other ideas about how to address this problem.  Please post any of those ideas in the comments section.

 

George Dawson, MD, DFAPA

 

 

References:

1:  Centers for Disease Control and Prevention (CDC). Indoor air quality at nine large-hub airports with and without designated smoking areas--United States, October-November 2012. MMWR Morb Mortal Wkly Rep. 2012 Nov 23;61(46):948-51. PMID: 23169316.

2:  CDC Health Alert Advisory.   Wildfire Smoke Exposure Poses Threat to At-Risk Populations.  Link

Update 07/06/2023: 

One week after turning off my air exchanger - the PM 2.5 in my house is down to 6 or essentially normal.  I talked with my air conditioning tech who also services the air exchanger and he agreed with the approach.

Image Credit:

Canadian Wildfire Smoke in Minneapolis

Chad Davis from Minneapolis, United States, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

file URL:  https://upload.wikimedia.org/wikipedia/commons/c/c0/Canadian_Wildfire_Smoke_in_Minneapolis_%2852907984452%29.jpg

page URL:

https://commons.wikimedia.org/wiki/File:Canadian_Wildfire_Smoke_in_Minneapolis_(52907984452).jpg

The Tomorrow River

 

The Tomorrow River is a small Wisconsin stream that crosses US Highway 10 three or four times between Fremont and Waupaca.  It eventually runs into a creek and becomes the Waupaca River.  I crossed all those tributaries twice on a trip last weekend. It gave me the usual opportunity to free associate to my past life. Two memories came immediately to mind – both from about 1977.  I was freshly out of the Peace Corps and trying to establish myself in a job as a research assistant cloning trees at an Institute in the area. That involved a lot of travel down Highway 51 to Highway 10 and I did not have a car.

One day I was travelling on a Greyhound bus heading to my apartment.  That was the first time I caught the Tomorrow River sign, as I looked up from a letter I was writing to my friend Glenn. I had a good experience in the Peace Corps entirely due to the Americans I met in my group.  They were bright, excitable, and energetic. We had gatherings where we listened to music, ate pizza, and played basketball.  We had long discussions into the night about what was important, what art meant, literature, music, math, science, and the meaning our work as high school teachers in the Peace Corps. We read the hipster literature of our time – Kerouac, Pirsig, Kesey, Brautigan, Wolfe, and others.  There were animated discussions and arguments.  All of that probably influenced the letter I was writing and then I saw the sign. The letter took on a surrealistic quality that Glenn appreciated in a letter he sent back to me.  As I visualized that decades old experience – it was a good feeling. I still feel a connection to my Peace Corps friends even though it has been decades and we rarely see one another or communicate.  I know that when I do – we will pick things up the way they have always been.

Between the second or third Tomorrow River sign there is an uphill curve in the road that bends to the left when you are traveling east. It is a long half mile bend. Later that same year just after Thanksgiving – I was getting a ride to my apartment from my friend Walt.  We went to the same high school and college. He was two years younger than me. Walt’s personality was completely the opposite of me. He was spontaneous, outgoing, and engaging. He could joke about anything.  I was the lab assistant in his organic chemistry section and one day his condenser hose broke loose and started spraying water just over the top of a freshly cut pile of sodium metal. I was able to grab the hose and redirect it.  Luckily there was no contact with the sodium, but after that point he started referring to himself and his lab partner as Captain Sodium.  On that day he was dropping me off and heading to his graduate program in endocrinology in Chicago.  The weather was not cooperating.  On that bend – the traffic that was usually travelling at 65-70 mph was at a dead stop in an ice storm and backed up for miles.  We both got out for a better view and realized it was impossible to stand on the road. Even  maintaining your balance, you eventually slid from the highest to the lowest part of the road and were forced to crawl back across the lane of oncoming traffic. We got back in the car and spent a long time joking about his bright reddish orange Dodge sports car and all of the trash talk he got from people in our home town about that car.  When he walked into a local bar he would hear: "Here comes the Fire Chief!"  We eventually completed the trip and I would see him from time to time over the next decades as he completed his PhD, then medical school, then residency in anesthesiology.  He became one of the top anesthesiologists in the country. And then several years ago, I got the news that he had died suddenly after a brief illness.  He was at the top of his game at the time – a department head and national expert in neurosurgical anesthesia.  I felt badly about not seeing him and not congratulating him on all of his success. I always feel badly when people don’t make it to retirement and a lot worse if I know them.  

Even before I went into the Peace Corps, I spent a lot of time navigating these roads with my friend Al.  We did that mostly in a 20-year-old Volkswagen beetle with a defective gasoline heater. When you tried to turn the heater on it might blow the hood open. Al was a mathematical genius and had accumulated almost enough math credits for a major when he was in high school - all self-taught by reading the texts. He decided to go to medical school and that led him to spend an additional 2 years as an undergrad taking the prerequisite courses.  Somewhere along the line driven by my insomnia and his sense of adventure, we ended up driving long distances to other towns at night to see movies or bands that we knew would never come farther north to our college town.  When you drive on roads in Wisconsin, Minnesota, and Michigan unusual things can happen.  When the pitch-black night is underlit by the snow cover – anything can happen. One night at about 2 AM we were on a road running parallel to Hwy 51 north when suddenly – an old model Chevrolet was airborne about 50 feet in front of us.  By airborne I mean it crashed over the top of a 5- or 6-foot snowbank at a high rate of speed and crossed our highway in a perpendicular path.   It landed on the other side of the road clipping the top of that snowbank first.  Turning around it was obvious that this was a planned attempt to launch the car from a parking lot outside of a bar to the other side of the road.  A few seconds later would have resulted in our Volkswagen being T-boned. That night we were able to turn up the radio and keep going.

These are the kinds of associations I have when I am driving these roads.  The paragraphs seem flat compared to the images in my head. I can envision my friends, our youth, images of what happened, the associated emotions, and the thoughts I have stacked on these events over the past 40-50 years. People I knew then often in a casual way.  People who I wanted to know better. People who – if I had interacted with them differently – would have drastically altered the course of my life and the people who did alter the course of my life. People who I wish would call me or send me an email.  People who I regularly think about and dream about.  But then I tell myself – “This is your own weird perspective on life – most people don’t think like this.”  Generally, that is good to know but at the same time – people do reach out from the past. They seem to realize that we are not the same people we used to be – but the common experience means something.  In many cases, it means a lot.  At my 50^th high school reunion, I was sitting outside of the main room when a classmate approached me and asked if she could sit down. I have known her for over 50 years and yet, that conversation was the longest I had ever spoken with her. It was longer than all of the conversations I ever had with her combined.  It was probably the best experience of the reunion.

I should probably clarify that I have no regrets and consider myself to be very fortunate.  All of these thoughts about the past don't cause regret - but there is often that feeling that you get when you go back to your home town for the first time. You see things in a different light.  You realize that you can't go back to the way things used to be. These thoughts have continuity with the present and the future.

At some point in the drive, I do a memory check.  I use the autobiographical memory test format and think of famous movie stars, visualize their image, and try to match names.  So far – so good.

I fantasize - primarily generative fantasies. I first encountered that term in the writings of the late Ethel Persons, MD.  She was an American psychoanalyst I found when I started to research fantasies in the 1990s.  She seemed to be one of the few psychiatrists writing about it. Generative fantasies are primarily problem solving fantasies that are more stimulating than coming up with lists in your head or your software. As I type that I am reminded of another road trip (east of Duluth on Hwy 2) when my wife asked me: "Do you ever have fantasies?' I told her I was fantasizing right at that time and she was very interested in the content. "I was thinking about what it would be like to win the men's 500M in the Olympics." She knew immediately that I was thinking about speedskating. I took up speedskating during residency and got quite good at it in my 40s. I was never an elite speedskater by any means, but I had the movements down, could endure the pain, and skated a lot of laps.  Part of learning the movement had to do with fantasies and thinking about the skaters I was seeing in the Olympics and racing against and remembering any advice I had received. I always have plenty of these thought patterns that seem focused on a hypothetical future.

 As a student of consciousness, I always wonder about how all of these thoughts are generated and (as a psychiatrist) what they might mean. Twenty years ago, I did a presentation on what I called the bus theory of the human brain. In computers, a bus is any system that connects components and allows data transfer between those components.  I decided that there was not enough emphasis on white matter and studied those tracts, their fiber content, and tried to calculate the bandwidth of those fiber tracts. At about the same time, I was wrapping up a course that I taught for many years on dementia diagnosis and cortical localization that was more of a behavioral neurology approach to the problem.  I tried to think of all of the recent papers I had pulled on hippocampal connectivity and recent papers on the neurochemistry of the hippocampus.  I thought about a paper I recently read on entropy and consciousness and whether thermodynamics could be a granular explanation for conscious states.  I am still a skeptic.

My wife wakes up.  We are driving home from her high school class reunion. There is a significant celebrity in her class and he sent a video when he could not make the reunion. The audio-visual equipment did not work, but we could see his projected image. We start to talk about the events of the night and what some of them might mean.  We talk about the A-V problems and the celebrity who clearly has become a projective test for everyone in her class. We talk about how good it will be to get back home and what we will need to do to reestablish the routine.

Thinking is a big part of life for me and life is very good…..

 

George Dawson, MD, DFAPA  

 

Photo credit for this one goes to my wife.  That is a Tomorrow River sign shot alongside Highway 10 last weekend.

References:

1:  Osanai H, Nair IR, Kitamura T. Dissecting cell-type-specific pathways in medial entorhinal cortical-hippocampal network for episodic memory. J Neurochem. 2023 May 30. doi: 10.1111/jnc.15850. Epub ahead of print. PMID: 37248771.

This Is How Civilization Ends...

I had that thought immediately after seeing the above graph on the CDC web site. Over a million new cases.  An all-time high by far.  At that point, the news had been heavy with discussions about the Omicron virus for about 3 weeks. The trail though Africa and Europe was described.  In the United States we had plenty of warning and plenty of time to adjust.  It wasn’t like that first peak in the fall and winter of 2020-2021.  Back then there were no vaccinations.  My wife an I finally got vaccinated in March of 2021 and then only by an extraordinary stroke of luck.  Before Omicron we were flush with vaccinations.  Two different retail pharmacy chains were scheduling appointments and they were free. When the booster came out that was also free and much easier to get. The overwhelming scientific evidence was that the immunizations were safe and effective.

The public health measures seemed less effective. That could be confirmed by a walk around Target or Walmart. At the absolute peak of mask wearing in Minnesota, my estimates were up to 30% of shoppers were masked. Half of those masks were loose fitting cloth masks and probably not very effective. Today, at the height of the Omicron spike 10% of the people in my coffee shop were masked and I was the only guy wearing an N95.  Despite an increasingly vocal group of aerosol scientists most people remain shockingly ignorant or willfully ignoring the airborne route of transmission. The most easily observed scenario is restaurant dining where the customers wear a mask to the table and then take it off to eat and talk for the next two hours. There is no magical protection from airborne virus in that scenario. Forget about the 6 feet safe distance rule at the start of the pandemic. Looking for restaurants that have improved their HVAC systems to improve airflow and air exchanges over time was also disappointing. So far in the Twin Cities Metro area I have found 1 restaurant. No restaurant or business as far as I know is posting their air exchanges per hour or carbon dioxide measurements to describe the potential risk of their environment. They are posting that they adhere to social distancing and all of the surfaces are wiped clean between diners.

Despite all of that inertia, the restaurants are packed.  Typically, shutdown occurs when a significant number of staff are ill with coronavirus and they cannot stay open. I dodged a bullet at Christmas just as infections were increasing. My wife and I were supposed to meet another couple at a restaurant. My suggestion to get take out and eat it at either of our homes was met with resistance. I was saved by a call from that restaurant that significant numbers of their staff were ill and they would be closing until things improved.   

The general cultural landscape has been even more grim. I follow all of the experts in the media on a regular basis – Drs. Fauci, Hotez, Jha, and Walensky.  On an average day they are awash in a sea of misinformation.  That sea contains the entrepreneurs who see the pandemic as a money-making scheme as well as the purely irrational who find that conspiracy theories about the virus, vaccine, and public health measures are easier to understand and believe than the science. Political opportunists are in the mix and as recently as today were suggesting that “white people” were being discriminated against and were less likely to get the vaccine as a result. The Florida Governor made this statement:

“We reject the biomedical security state that curtails liberty, ruins livelihoods and divides society.”

Biomedical security state? The politicization of this pandemic knows no bounds. It obscures both the science and goodwill toward the scientific and medical communities.  But it doesn’t stop there.  In some large health care organizations 10% of the workforce has been fired for not complying with workplace mandates on COVID-19 immunizations.  Some of these workers are physicians who should have been taught basic epidemiological concepts – the most basic being that vaccinations are a rare medical miracle that have saved the lives of tens of millions of people.  Disease have been eradicated, prevented, and the course of infectious diseases has been altered.  And even if you are not a physician, everyone has the experience of taking all of the mandatory vaccinations required to attend school.  Most of these vaccinations had a significantly worse side effect profile than the currently available COVID-19 vaccinations.

Apart from reducing rates of infection, hospitalization, and death these modern vaccinations also reduce the risk of chronicity. Chronic or “long COVID” symptoms might occur in as many as 70% of patients after the infection. Remission rates and rates of disability are still being determined at this time.  Given the risk/benefit considerations of the vaccinations it is difficult to see how any rational person would refuse it.  It is even more difficult to understand how a rational person would not take basic measures to protect themselves and their families from airborne virus or justify ignoring the pandemic on the basis of a completely implausible conspiracy theory. In some cases, the motivations are very clear.  Politicians would rather use various forms of rhetoric to attack the idea of a pandemic and what it takes to resolve it for political gain rather than taking positive steps recommended by experts. It is a standard political tactic.  That rhetoric has been advanced to extreme levels and to the point where scientists and their families are being threatened.  Today the suggestion that “white people” were being discriminated against struck me as white nationalist rhetoric.  It was viewed just as another “falsehood” in the media.  Certainly, blind partisan acceptance of these statements is not very likely to exhibit flexibility in thinking about the pandemic, the virus, or possible solutions.

The press has stepped in and commented on the process as a “mass delusion” or “mass psychosis” as if the use of psychiatric jargon by a journalist would add credibility to the criticism of many people thinking and acting irrationally. Many of them are agitated, visibly angry, and can become aggressive typically when confronted about pandemic precautions in schools and businesses.  Hardly a day goes by without seeing an airline passenger or town hall meeting participant screaming until they are red in the face and carted away by security. None of these people has a psychiatric disorder.  They can cool off somewhere, suppress their irrational thoughts and the associated anger, and get up and go to work the next morning.  During the run up to the 2020 Presidential election there was heated commentary about President Trump’s mental health and fitness for office. There was some debate in the psychiatric community if it was appropriate to discuss that issue based on Trump’s observed behavior rather than a psychiatric assessment. This essay looks at the other side of that debate. Why do so many people follow leaders who make repeatedly false statements that in some cases are viewed as potentially inciting people to do the wrong thing? And conversely – how do so many people accept the more obvious rational path and reject all of the paranoia and conspiracy theories?

There are of course numerous theories about how this comes about.  The theories generally depend on the same theories that have been used to describe normal development, psychopathology, and normal learning processes.  In some cases the theories have a philosophical basis – that seem to be fashionable these days. And despite many of these theorists incorporating a neurobiological model – very little explanation about how that is relevant.

The relevance is obvious to me starting with the relationship between emotion and cognition specifically decision making. In order for it to be obvious, the relationship between emotions and normal decision making needs a brief exploration. Human decision making typically occurs as an integrated process in the frontal cortex. I won’t digress into any subdivisions or tracks in this post. The key word here is integrated. That means the frontal cortex takes a large number of inputs and uses them to varying degrees in the ultimate decision. That includes a lot of memory input, specific types or learning, emotional input, and real time sensory and perceptual data.  The amount of input is large and much of it occurs at an unconscious level. How it occurs is largely unknown at this point but with our limiting inputs have been determined.  One of those inputs is emotion. We know for example from lesion studies that emotional input is absolutely critical for normal day to day decision making. Of the vast number of potential decisions we all have a subset that are associated with emotional valences that can affect our preferences. Without access to those valences decision making slows and grinds to a halt.

Restricting our consideration of the decision space to all of the possible decisions about the pandemic and how to proceed – all of the medical, scientific, personal, political, manipulative, and conspiracy theories the possibilities are very large. If we have 300 million decision makers and they all have unique conscious states and personal capacities for decision making the potential outcomes are large. It is also a more complex scenario than all of the typical explanations for pandemic denial.  Each one of our 300 million decision makers has unique experience affecting the emotional valences of their decisions. The overt decisions may seem to coalesce at some points but for many different reasons. For example, believing what a politician says despite the clear documentation that they are lying can occur as the result of identification with similar people in the past, identification with a general class attitude or ethos that it represents, or it simply could be activated by the angry emotion that politician effects. Those are just a few possibilities.

The pandemic vaccination vs. anti-pandemic antivaxx is by definition a binary polarized debate – the reality based on what we know about how the brain works it is far from that simple.  Even on what appears to be the rational side there is no Spock-like analysis.  The public health experts are all accessing emotion when making their decisions. Rational thought is reward-based learning and associated to one degree or another with a “Eureka” moment.    

The key question going forward is what can be done to address the degrees of freedom associated with the possible decisions of this brain process.  What can be done to improve the process and by improve, I mean assure that civilization survives the current and potentially more lethal pandemics. To that end, there are numerous cinematic depictions of apocalyptic pandemics. Based on the depictions prior to this pandemic they are probably fairly accurate. Once a lethal pandemic takes hold, the decision space for survival collapses as fewer and fewer decisions are possible. An intuitive writer or film maker knows that at some level.  Time to make it general knowledge.

 

George Dawson, MD, DFAPA

Airborne Transmission - Once Again!

 

I thought I would take time for a rare celebration on this blog.  Most of my writing is about probabilities and uncertain outcomes. In many cases I am responding to the same tired arguments from people who don’t understand science, biology, medicine or psychiatry. Those positions generally result in some political attacks based on that lack of understanding or some specific political agenda. The position I am referring today is the airborne transmission of viruses. Although it seems like a straightforward scientific issue it has led to as much controversy as any psychiatric topic. Despite a significant amount of literature out there on airborne spread, there has been nothing but resistance to the concept.

Nowhere was the resistance more evident than the advent of the current SARS-CoV-2 pandemic. Initially the message was that the virus was spread by fomites or intermediate size droplets that fall within a few feet following a cough or a sneeze.  Accordingly, social distancing at more than a few feet, decontaminating hands and surfaces were recommended to counter this mechanism of transmission. Many experts claim that most respiratory viruses with very few exceptions are transmitted this way. Those same experts claim that airborne transmission of viruses in smaller droplets travelling much longer distances was controversial at best. All of those conflicting ideas led to recommendations for no masks in February of 2020 followed by recommendations for masks in the next two months.  The mask recommendations occurred in the context of widespread shortages of personal protective equipment (PPE) for health care workers.   

I posted my qualifications on the matter (2 Avian Influenza Task Forces earlier in this century, being subjected to multiple respiratory virus epidemics at work despite rigorous hand washing, and studying the available engineering and viral data, and lengthy discussions with HVAC experts) and began to write about it on this blog.  My perspective is clearly that respiratory viruses are airborne and therefore will not be stopped by handwashing alone, that there are clearly engineering approaches to stop respiratory viruses that will work much better than just handwashing, and that there should be a major research and development effort on environmental designs to minimize and even stop respiratory viruses in homes and public building. In fact, as I type this I have selected a UVC device to be installed in my home HVAC system and it will probably be installed in the next month or two.  Many of those posts on this blog can be found here or by using the search term “airborne” in the search box.

The victory lap today occurs with a press release from the CDC today that I consider a bombshell in terms of the airborne transmission concept.  The press release is a quick read but it highlights why surface contamination is unlikely to be a significant factor:

“Quantitative microbial risk assessment (QMRA) studies have been conducted to understand and characterize the relative risk of SARS-CoV-2 fomite transmission and evaluate the need for and effectiveness of prevention measures to reduce risk. Findings of these studies suggest that the risk of SARS-CoV-2 infection via the fomite transmission route is low, and generally less than 1 in 10,000, which means that each contact with a contaminated surface has less than a 1 in 10,000 chance of causing an infection.”

And further:

“The principal mode by which people are infected with SARS-CoV-2 is through exposure to respiratory droplets carrying infectious virus.”

This information has been slowly presented over the course of the past several months.  For example, Dr. Fauci mentioned on several news outlets that cleaning all of the mail and groceries was not necessary because it was not considered a main route of transmission. A logical inference from that statement is why there is a concern about any surfaces at all unless there is a person with a known infection close by.  And by extension, if surface contamination is not that much of a problem why the concern about accidentally touching your face?  As Dr. Fauci typically states we now have the science behind the transmission and the recommendations can be adapted to the new findings.

The CDC press release does not come right out and say airborne transmission.  They continue to say respiratory droplets are the predominate mode of spread and the old document on respiratory droplets says nothing about differentiating between moderate sized droplets that typically fall to the ground within a 6-foot radius of where they are generated or airborne droplets that are lighter, spread past 6 feet from the generation site and remain suspended for longer periods of time.

Some of the comments on the press release have been much more definitive. The only reference to this post has a good timeline on the airborne controversy and this quote from atmospheric chemist Jose-Luis Jimenez: “If we took half the effort that’s being given to disinfection, and we put it on ventilation, that will be huge.”  In the same reference Germany has invested a half billion dollars in improving ventilation and indoor air quality.

Overall, it appears that the CDC is slowly coming around to the idea that respiratory viruses are transmitted via airborne routes, but some resistance is still evident in the press release they link to an earlier non-descript respiratory droplet transmission document.  There are many potential advantages to fully backing the airborne transmission concept (in addition to the available science).  Research and development is at the top of the list. In an early blogpost, I pointed out that UV decontamination was routine in buildings when I was a kid in a small town in northern Wisconsin.  The currently available UVC is much safer and very effective for killing airborne biological particles. From a clinical trials perspective, deployment of these systems on a large scale and following the number of respiratory infections in facilities with and without the technology seems like a fairly basic experiment.

It is also interesting to consider the resistance. There is undoubtedly politics in science and that can be a factor. There may be a medical intervention bias. In other words, we need some magical intervention like a vaccine, antiviral medication, or general polypharmaceutical modality that can either cure or prevent the excessive morbidity and mortality from respiratory viruses.  The track record there is some wins and many losses.  Every year various populations around the world are subjected to significant effects from flu-like illness that are nowhere as lethal as SARS-CoV-2.  Remarkably – everyone accepts this state of affairs until a more lethal virus comes around and affects a larger group of people.  There is politics as usual leading to irrational attitudes about viruses and physical interventions.  The appropriate environmental interventions may make mask refusers irrelevant at some point in the future.

The bottom line of today’s release is good news for all of the airborne virus crowd and I definitely consider myself in that crowd. I would still like to see the CDC modify their position on transmission in respiratory droplets and I think that is coming.  But most of all, I would like to see us get serious about using environmental measures to limit the exposure and spread of all respiratory viruses including the current one that has killed far more Americans than any influenza epidemic since 1918.

 

George Dawson, MD, DFAPA

 

References:

1:  Lewis D. Why indoor spaces are still prime COVID hotspots. Nature. 2021 Apr;592(7852):22-25. doi: 10.1038/d41586-021-00810-9. PMID: 33785914.

2: Dietrich WL, Bennett JS, Jones BW, Hosni MH. Laboratory Modeling of SARS-CoV-2 Exposure Reduction Through Physically Distanced Seating in Aircraft Cabins Using Bacteriophage Aerosol — November 2020. MMWR Morb Mortal Wkly Rep. ePub: 14 April 2021. DOI: http://dx.doi.org/10.15585/mmwr.mm7016e1

3: Greenhalgh T, Jimenez JL, Prather KA, Tufekci Z, Fisman D, Schooley R. Ten scientific reasons in support of airborne transmission of SARS-CoV-2.  The Lancet (online).  Published 4/15/2021. https://doi.org/10.1016/S0140-6736(21)00869-2  Current link

4: Tang JW, Bahnfleth WP, Bluyssen PM, Buonanno G, Jimenez JL, Kurnitski J, Li Y, Miller S, Sekhar C, Morawska L, Marr LC, Melikov AK, Nazaroff WW, Nielsen PV, Tellier R, Wargocki P, Dancer SJ. Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). J Hosp Infect. 2021 Apr;110:89-96. doi: 10.1016/j.jhin.2020.12.022.  Current Link

Covid-19 Up Close and Personal

 On September 4, I started to feel typical symptoms of a flu-like illness. I have been a student of flu-like illnesses for at least the past 15 years. Some may say that I am obsessed with flu-like illnesses. By definition these illnesses start out as acute upper respiratory infections but also lead to systemic symptoms like malaise, weakness, and muscle pains or myalgias. In some cases, the symptoms can build to a disabling intensity. About five years ago I developed a flu-like illness after returning from Alaska that led to an exacerbation of asthma. I had not taken any asthma medications for 20 years but have been on those medications ever since. Researching that area suggested that flu-like illness was probably a rhinovirus. Some researchers think that rhinovirus is one of the main precipitants of asthma. Rhinovirus also happens to be a common circulating respiratory virus along with about 20 others that cause respiratory infections every year.  There are several non-COVID-19 coronaviruses in this group.

There were definite early signs even before the first respiratory symptoms. I have a fairly set exercise routine that I do every week and I noticed that my baseline heart rate (54 bpm) and blood pressure (105-110 mm Hg systolic) were increased and my exercise capacity was decreased by about 40%. That occurred about 48 hours before the onset of symptoms. As the symptoms increased my first thought was that I needed to get tested for coronavirus. That took an additional four days. It wasn’t from a lack of trying, but more a lack of resources going into the weekend. That delay highlights a significant weakness in the American healthcare system. I self-quarantined during that time but there are a lot of people who would need to see the test result before they could.  I did get positive test on day seven, I canceled the rest of the day at work and have been home recovering ever since.

The overall course of the illness has been very similar to a moderate case of influenza with the exception that I did not get a fever. It measured every day in the normal range. I also did not get shortness of breath.  Having the risk factors of asthma and old age, I was fairly anxious about any shortness of breath as a symptom. My symptoms are basically as graphed with a few exceptions of what I would refer to as atypical symptoms. The first one would be feeling flushed or like the skin temperature is elevated. That has been a fairly consistent feature that I have not seen mentioned anywhere. My skin was always cool to the touch and not moist. Another atypical symptom is laryngitis.  I have observed that in several COVID-19 patients in the media.  It can be fairly limiting if you have to talk all day at work like I do. The third atypical symptom was viscous mucus in the nose and throat. It was not abundant but difficult to clear and never reached the volumes typically seen in bronchitis.

One of the questions that I have been asked is: “How does a guy as careful as you end up catching COVID-19?”  It turns out that is an excellent question. As noted elsewhere on this blog I have essentially self-quarantined at home since the end of March or the start of the pandemic. I have had limited contact with people. I do not go into stores, supermarkets, coffee shops, or any public space. I pick up groceries ordered online and then collect them from a site where a masked attendant loads them into the back of my SUV.  All of my clinical work, continuing education, and professional meetings are done online.  I prepared a timeline of all contacts in or around my home for the previous 19 days (click to enlarge).  

From the summary, of the 18 total contacts I had direct contact with 6, only 4 of them about 6 days prior to the onset of symptoms.  All 4 of those contacts were wearing masks and none have tested positive for COVID-19.  My wife had contact with the other 12 and 9 of them were socially distanced or masked.  Only the electrician and three of the appliance repair/installers were not but they were socially distanced.  In addition, we made an effort to air out the house when they were there and after the left.  There was a total of 5 tradesmen in the house. They were all there for an average of about 1 hour.  I greeted one of them at a distance of about 12 feet and he was not wearing a mask. According to a recent hierarchy of transmission risk, I had no high-risk contacts for transmission (3).

My wife on the other hand was in a couple of higher risk scenarios (but not much higher).  As an extrovert, she was also out talking with people every day and exercising with several of her health club friends at their homes. She did however test negative for COVID-19 on the exact same test that I took. There are various estimates that 20-40% of COVID-19 infections result in asymptomatic carriers. It may be possible that she was a carrier and subsequently cleared the virus so that no viral RNA was detected on the nasal swab.  We are both currently trying to get antibody testing to COVID-19. It will confirm that I have short term immunity and possibly that my wife was an asymptomatic carrier.

When I did find out that I tested positive, I self-quarantined in the house pending my wife’s test and have been quarantined ever since.  The health plan recommendation is to wait for day 14 and if asymptomatic at that point, the self-quarantine can end. My wife is using the same date to end her quarantine and remained asymptomatic.  We have the luxury of having a large enough house where we can occupy separate areas and have separate bathrooms that are exhausted to the outside of the house.  I also kept an electronic air filter with a UVC germicidal light at the entrance to my office and between us in any public areas.  Several questions arise from this experience including:

1.  Why were my symptoms so mild (relatively speaking)?

Considering the actual statistics of the pandemic in the United States – my outcome is not that surprising.  About 1 in 34 cases have died and that number increases to 1 in 13 in my age range and 1 in 5 in the next highest age decile.  At the time of this posting there have been 197,000 deaths and 6.7 million cases.  There is a lot of comparison with influenza, but at this time there should be no mistake that while influenza typically generates more cases and more hospitalizations – there has only been one year where influenza mortality exceeded current SARS-CoV-2 mortality and that was the pandemic of 1918. 

The second consideration are the physical parameters of the environment. Assuming that my wife is not an asymptomatic carrier, the only time I was at a distance of less than 4 meters I was wearing a mask and so were the people I was in proximity to.  The contact lasted less than 10 minutes. And not a lot was said. We know that masks, distancing, and dilution in outdoor air probably works be reducing the concentration of airborne viral particles.  With that reduced concentration, any inhaled inoculum will be less resulting in a less severe infection. The estimated number of viral particles necessary to precipitate a case of COVID-19 is about 280 particles. That is 2-3 orders of magnitude higher than more virulent and lethal viruses like smallpox.

A few other lifestyle considerations. I eat a high-protein, high fiber, high whole grain, and low fat/low sugar diet.  I try to maintain a healthy weight.  I drink a lot of fluids every day.  I have been doing that for at least 30 years on the advice of a rheumatologist in order to maximize uric acid secretion and decrease the risk of gout attacks (I am an undersecretor of uric acid and had my first gout attack in medical school). Anyone reading this should drink a lot of fluid only based on their physician’s advice.  The only relevant factor in this paragraph in surviving the virus is probably maintaining a healthy weight and a good diet.  I was able to maintain my usual fluid intake during the course of this illness.

I take Vitamin D every day because my levels are typically marginal.  I take famotidine daily to prevent anaphylactic reactions. I only take it because the original H-2 antagonist recommended by my allergist (ranitidine) was taken off the market because of contamination in the manufacturing process. There has been some suggestion that famotidine is useful in the prevention or treatment of COVID-19 and for a while it nearly disappeared off the generic market.  I am not aware of any randomized clinical trial (RCT) results of famotidine and it has been demonstrated to not have any direct antiviral effect in vitro.  There is current speculation that in combination with H-1 antagonists that it may reduce histamine associated cytokine effects (13). At this point I would not consider it to be too relevant.

Exercise is a big part of my life and has been for the past 30 years. I typically exercise vigorously for 90 to 120 minutes per day.  Recent research (11,12) suggests that people who exercise vigorously into old age have better acute adaptive immunity (T-cell response) due to a better thymic environment.  One of the purported mechanisms is IL-7 production by skeletal muscle.  IL-15 is also an exercise responsive interleukin that enhances T-cell survival.  The net effect of these changes in the older person who exercises vigorously has a greater input of thymocyte progenitor cells and an enhanced output of CD4 and CD8 cells that are recent thymic emigrants (RTE). Both of these cells populations are critical for the acute adaptive response to novel viruses.  If I had to speculate about the lifestyle factors that are important it would probably be the effects of exercise, diet, not smoking and no alcohol intake on immunity and pulmonary function.

 2.  Why is there such heterogeneity in responses?

The host determinants of response are not well characterized at this point- other than the suggestion that previous exposure to common circulating coronaviruses could possibly lead to an enhanced antibody effect and either apparent asymptomatic carrier status or a less severe case as an adult.  Is it possible that the severe respiratory infection that I got in January was a coronavirus that was not SARS-CoV-2 and that it conferred some immunity?  This is one of the theories about why children are less affected by COVID-19 than adults – they tend to get more respiratory virus infections per year. Human coronaviruses and rhinoviruses are generally considered to cause up to 50% of common cold infections per year (10).  The Minnesota Influenza Incidence Surveillance Project, (MIISP) 3 of the 4 normally circulating human Coronaviruses – NL63, HKU1, and 229E (not OC43) since last September. Although these coronaviruses are now considered all part of the collection of common cold viruses they have been fairly recent discoveries with NL63 discovered in 2004 (7) and HKU1 discovered in 2005 (8).  The common coronaviruses have considerable RNA sequence homology with SARS-CoV-2 suggesting cross immunity can exist (9).  For example, pre-existing T-cell immunity in blood donors to SARS-CoV-2 is documented and is thought to be due to exposure to beta-coronaviruses that are in circulation (4).  But there is also evidence suggesting that pre-existing coronavirus immunity is not effective with SARS-CoV-2 (15).

One the genetic side, there are essentially no data at this point about genetic factors that favor successful recovery from the pandemic virus (click to enlarge).

 

3.  Given the exposures – is it possible that some other exposure (packaging, mail, aerosols from washing packing or mail) is more important than suggested by conventional wisdom?

Even though handwashing and washing of frequently touched surfaces is a top recommendation the current opinion is that transmission is unlikely from either groceries or mail based on studies that look at virus survival on different materials over time.  To me that is somewhat inconsistent with the hand washing advice.  The original theory was that a person could touch a contaminated surface, touch their face, and then end up with the infection through mucus membranes.  Groceries and the mail seem to be designated as infrequently touched surfaces relatively free from contamination.  An additional question for consideration is whether aerosols generated in washing the surfaces of groceries can transmit. SARS-CoV-2.  I use a UV sanitizer for mail and any objects the size of a large book or smaller. That method has limitations in terms of how accessible the surfaces of any contaminated object are.

One final critical consideration is the person you are in quarantine with. Do they share your goals and risk tolerance or not?  In my particular case, I am not risk tolerant at all if the risk is contracting a virus that has a 1 in 13 chance of killing me.  The prior probability of an adverse outcome is higher due to me having asthma, but the exact numbers are probably not known at this time. I would happily remain at home, not get a haircut (I have not), and just go out for groceries and necessary medical care.  My wife on the other hand is very social, and has maintained an active schedule with her friends and associates over the entire pandemic.  She spends her days exercising, socializing, and attending limited activities with friends.  She is distanced and wears a mask when necessary. Despite our ability to pick up groceries without having to enter a store she will spontaneously stop at these stores, put a mask on, and pick up a few items. This difference in approaches to the pandemic does create some tension.

Whether our different approaches produced predictable outcomes or not is up in the air at this point.  She was just approved for antibody testing and I still have to get approval at an appointment next week. All we know is that I was positive for SARS-CoV-2 on a PCR test and she was not. That leaves either airborne transmission, contaminated surfaces, or aerosols from washing contaminated services.

Getting through this does provide a sense of relief.  Even though immunity to this virus does not seem to be permanent at this point I am very grateful to have made it through these two weeks.  My boss sent me an email and asked what that sense of relief was like and I told him:

“It feels like I dodged a bullet.”

And it does…..

 

George Dawson, MD, DFAPA

 

References:

1:  Stephens DS, McElrath MJ. COVID-19 and the Path to Immunity. JAMA. Published online September 11, 2020. doi:10.1001/jama.2020.16656

2:  Gandhi M, Beyrer C, Goosby E. Masks Do More Than Protect Others During COVID-19: Reducing the Inoculum of SARS-CoV-2 to Protect the Wearer [published online ahead of print, 2020 Jul 31]. J Gen Intern Med. 2020;1-4. doi:10.1007/s11606-020-06067-8

3:  Jones Nicholas R, Qureshi Zeshan U, Temple Robert J, Larwood Jessica P J, Greenhalgh Trisha, Bourouiba Lydia et al. Two metres or one: what is the evidence for physical distancing in COVID-19? BMJ 2020; 370 :m3223 Link

4:  Stephens DS, McElrath MJ. COVID-19 and the Path to Immunity. JAMA. Published online September 11, 2020. doi:10.1001/jama.2020.16656 Link

5:  Fischer EP, Fischer MC, Grass D, Henrion I, Warren WS, Westman E. Low-cost measurement of face mask efficacy for filtering expelled droplets during speech. Sci Adv. 2020;6(36):eabd3083. Published 2020 Sep 2. doi:10.1126/sciadv.abd3083 Link

6:  Bar-On YM, Flamholz A, Phillips R, Milo R. SARS-CoV-2 (COVID-19) by the numbers. Elife. 2020 Apr 2;9:e57309. doi: 10.7554/eLife.57309. PMID: 32228860.

7:  Fouchier RA, Hartwig NG, Bestebroer TM, Niemeyer B, de Jong JC, Simon JH, Osterhaus AD. A previously undescribed coronavirus associated with respiratory disease in humans. Proc Natl Acad Sci U S A. 2004 Apr 20;101(16):6212-6. doi: 10.1073/pnas.0400762101. Epub 2004 Apr 8. PMID: 15073334; PMCID: PMC395948.

8:  Woo PC, Lau SK, Chu CM, Chan KH, Tsoi HW, Huang Y, Wong BH, Poon RW, Cai JJ, Luk WK, Poon LL, Wong SS, Guan Y, Peiris JS, Yuen KY. Characterization and complete genome sequence of a novel coronavirus, coronavirus HKU1, from patients with pneumonia. J Virol. 2005 Jan;79(2):884-95. doi: 10.1128/JVI.79.2.884-895.2005. PMID: 15613317; PMCID: PMC538593.

9:  Yaqinuddin A. Cross-immunity between respiratory coronaviruses may limit COVID-19 fatalities. Med Hypotheses. 2020 Jun 30;144:110049. doi: 10.1016/j.mehy.2020.110049. Epub ahead of print. PMID: 32758887; PMCID: PMC7326438.

10:  Greenberg SB. Update on Human Rhinovirus and Coronavirus Infections. Semin Respir Crit Care Med. 2016 Aug;37(4):555-71. doi: 10.1055/s-0036-1584797. Epub 2016 Aug 3. PMID: 27486736; PMCID: PMC7171723.

11:  Duggal NA, Pollock RD, Lazarus NR, Harridge S, Lord JM. Major features of immunesenescence, including reduced thymic output, are ameliorated by high levels of physical activity in adulthood. Aging Cell. 2018;17(2):e12750. doi:10.1111/acel.12750

12:  Lazarus NR, Lord JM, Harridge SDR. The relationships and interactions between age, exercise and physiological function. J Physiol. 2019;597(5):1299-1309. doi:10.1113/JP277071

13:  Hogan Ii RB, Hogan Iii RB, Cannon T, et al. Dual-histamine receptor blockade with cetirizine - famotidine reduces pulmonary symptoms in COVID-19 patients [published online ahead of print, 2020 Aug 29]. Pulm Pharmacol Ther. 2020;63:101942. doi:10.1016/j.pupt.2020.101942.

14:  Minnesota Influenza Incidence Surveillance Project,  (MIISP). Minnesota Department of Health.  Correspondence on circulating common coronaviruses in Minnesota.  Received on 9/19/2020. 

15:  Loos C, Atyeo C, Fischinger S, Burke J, Slein MD, Streeck H, Lauffenburger D, Ryan ET, Charles RC, Alter G. Evolution of Early SARS-CoV-2 and Cross-Coronavirus Immunity. mSphere. 2020 Sep 2;5(5):e00622-20. doi: 10.1128/mSphere.00622-20. PMID: 32878931; PMCID: PMC7471005. 

Supplementary 1:

My wife tested negative for SARS-CoV-2 IgG antibodies today (9/22/2020) in addition to the negative nasal swab PCR tests - making her an unlikely source of infection.

Supplementary 2:

COVID-19 follow-up: 

Saw my internist yesterday (9/25/2020). 

My course of the illness was "average" for all of the patients he has seen. He agreed that PCR false positives are not likely but false neg are. He declined Ab testing. I applied to the Red Cross convalescent plasma program.

       

Airborne Transmission Denial Dies Hard ........

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/),