Federal Employees News Digest
As feds head back to work, questions remain on how COVID-19 spreads
- By Nathan Abse
- May 18, 2020
Since March, approximately 85,000 Americans have died from the novel coronavirus. Yet with infections still increasing, federal employees and other workers are returning to their regular workplaces in growing numbers. Even those who are not re-entering the workplace face rising risks of COVID-19 exposure as states begin “opening up.”
Proponents of relaxing controls argue that federal bailouts of over $3 trillion and 15% unemployment rate means the costs of tight controls have become more intolerable than the disease. Opponents, however, insist testing and tracing capacity remains lacking and -- citing renewed shutdowns in Germany and South Korea after initial restrictions were loosened -- predict spikes in COVID cases and deaths here.
In a nation of generally weak testing and tracing systems, the best bet for feds is to remain alert and try to minimize the risks of catching and transmitting the disease. With no available vaccine, scientifically informed personal decisions are the only means to break the contagion chain.
This week, Nathan Abse interviews one of the country’s top experts on airborne transmission of pollutants and pathogens, William Bahnfleth, a professor of architectural engineering at the Pennsylvania State University and presidential fellow with the American Society of Heating, Refrigerating and Air-Conditioning Engineers. Bahnfleth is also a fellow with the International Society for Indoor Air Quality and Climate and an expert on bioaerosol contaminants.
This interview has been edited for length and clarity.
As an expert on indoor air safety, have you found if the novel coronavirus can infect individuals after a virus-positive person leaves a room?
Bahnfleth: We actually don’t have proof yet about how much risk there is except for short-range transmission. That’s why maintaining at least six feet is so important. But longer distances and time frames are very possible. The process that’s in play is this: The virus gets in the air in quantity just from a person breathing, exhaling, because the person is producing small droplets when they are breathing out. Anyone can shed virus this way, and therefore there may be virus in these droplets that are emitted and hang in the air.
How are those droplets can be dangerous?
Bahnfleth: The droplets have a range of sizes, on the particle scale. They can range from very small to, well, pretty big. They can come out as liquids. A drop of mucus -- mostly liquid -- that contains virus, or viruses, that’s a “droplet” and generally falls to the ground and other surfaces pretty quickly. But some droplets are smaller, and if those are in the air long enough, the liquid evaporates off and they become what is sometimes called “droplet residue.” They can remain in the air longer -- in some cases, much longer -- and they can travel. They are potentially dangerous as they can be inhaled by others that share that air.
How do people contract COVID-19?
Bahnfleth: Again, the theory currently in play with most experts is that the virus is primarily transmitted from hands and surfaces, or transmitted by larger droplets, ones that don’t move very far through the air. Larger particles settle, due to gravity, so they fall before they hit someone, unless someone is within a short distance -- one meter, two meters, something in that range. Physical contact, from touching and surfaces, and people being physically close to each other is the other way we think people get infected.
So breathing in close proximity to an infected person and picking up the virus from contaminated surfaces are thought to cause the majority of infections?
Bahnfleth: Yes. And remember, the same person who is careful and avoids getting the virus -- who avoids having it land on their face or breathing it in directly -- can of course still get it right there, in the same space, by other means. They might touch something nearby and get it on their hands. They then can touch their face, eyes or nose or mouth and easily transmit material to their own mucus membranes, causing an infection. This is generally believed to be the No. 1 way the virus was being transferred -- hands to face. This is why you hear “wash your hands” so often.
If COVID-19 usually infects another person via close breathing or sneezing or by touching the face, why isn’t avoiding those things good enough?
Bahnfleth: Because while most infections occur by way of hands transferring the virus to the face or by close contact, not all transmissions happen in these two ways. There is another possible way: through the air, where enough of the virus travels farther and remains airborne, to infect someone else. These particles where the liquid has evaporated from the droplet can be moved around by air currents, within a space, and someone else can inhale them and become infected -- even someone who is more than six feet away and maybe even some time after the initial, infected person who expelled those viral particles has left the area. This is not proven, but it is possible.
How long might these airborne particles remain a threat and in what kinds of spaces?
Bahnfleth: That’s the controversy at the moment: To what extent do these very small particles, which have been found to remain aloft for some time, actually transmit virus to others and cause new infections? This is a very active subject for research right now. I want to be clear, though -- it is a real possibility. Sampling has shown that sometimes there is live virus in the air hours -- literally hours -- after an infected person who shed that virus has left the area. Researchers also have found live virus days on surfaces even days after an infected person has left the area. This is evidence that infections, perhaps, can be caused by these routes.
Are there any other interesting details in the research on ambient airborne COVID-19?
Bahnfleth: There is theoretical analysis and modeling and other evidence showing that even at close range it is not just the larger particles that can be inhaled to cause a new infection. It can also be the smaller particles in play. Now the thing that we haven’t really agreed on -- or what I as an engineer, at least, do not yet know -- is this: What is the effective minimum dose of this particular virus, how much of it is necessary to cause a new infection? This information is crucial. The point is, a person who is creating this infectious aerosol is creating what we call a “point source.” The farther you get away from the origin of that cloud, that point source, the more diluted the virus is. Is it really infectious at a given distance? Or is the ventilation in a given space good enough such that at this or that spot, where another person might be, there is not enough virus to cause a new infection? The research is ongoing.
So that’s a key problem, still: determining the minimum dose that causes infection?
Bahnfleth: Yes. Some pathogens - -some viruses -- require a small dose to cause an infection, while others require a much higher dose to be absorbed or inhaled for a person to get sick. For example, tuberculosis in low doses is very infectious, by way of this airborne route. It’s really the main way you get TB, by inhalation.
What are some ways other than telework that workplaces can be made safer?
Bahnfleth: First, without going into the details of research that’s been coming out, you have to make some decisions. If you’re tasked with designing HVAC systems, like I am, the question is: Do you proceed in your designs and plans as if the virus could be communicated through the air at a distance? The answer is yes, we need to act as if that is the case. Just about every organization that represents the HVAC community has come down on the side of caution. We don’t have great evidence that it does happen, but we don’t have evidence that it doesn’t happen either.
Second, you have to start working on solutions. We believe that even at short distances, greater air dilution and movement -- ventilation to dilute the virus -- can be helpful. That’s where we in my profession are at with this. A lot of our proposed solutions are about increased ventilation -- bringing in more outside air -- along with using filters to remove more of the virus. In addition, other treatments to get rid of the virus are proposed -- such as certain kinds of ultraviolet light or putting the air through powerful HEPA filters. Some are proposing heating -- thermally destroying pathogens -- or irradiating the air. There are many possibilities.
What about the air on public transportation?
Bahnfleth: I’m not specialized in transportation. With respect to buses, I have talked to others who are knowledgeable on this subject, and I’ve been told that the filters used on buses are typically not better than what we use in commercial buildings. And because of that, they are not particularly effective at catching respirable particles, particles that you can breathe deep into the alveoli of your lungs and that -- depending on the dose -- can cause infection. In buses, though, there is talk of coming up with ways to mix in more outside air. That could help.
Many of our readers work at health care facilities, such as those run by the Department of Veteran Affairs. Can the ambient air in those buildings be dangerous?
Bahnfleth: Yes, it can be, depending what is going on in that space. That’s why medical personnel and others there know that medical-level masks and protection are necessary. Generally, medical buildings and health care environments have much higher levels of air filtration than other buildings. Places like that have more air recirculation -- meaning that you take the air from the space through much higher efficiency filters than in other spaces. If you can get high enough filtration in a medical setting, it helps a lot to make the air safer, because almost everything gets caught in those filters. For comparison, in some commercial buildings there might be, say, one “air change per hour,” but in a medical setting you might have one air change per hour, in the sense of new air from the outside, but fully 12 changes per hour in terms of how many times that air travels through the filter system. Much more filtration. These are just examples -- it’s certainly not how every medical space is.
What’s the bottom line about longer range airborne transmission of COVID-19?
Bahnfleth: I see no reason to doubt that, with COVID-19, there has been a lot of short-range [airborne] transmission. The best evidence is that the physical, social distancing, where we see people spacing themselves, is working. There are fewer infections, and it seems to have the desired effect, especially in places where people had been mingling and the transmission was happening faster. Of course, other modes of transmission also exist, like the one we are looking into here -- perhaps longer-range [airborne] transmission. We should err on the side of caution. The evidence is not definitive, but in some cases it is strongly suggestive. I have read and researched enough to say long-range airborne transmission is plausible. Do we need more filtration, do we need other design changes? We don’t have enough information to know all of what we need -- yet -- but we are doing things in response to the situation that make sense, I believe.