Doc. Phd Jakob Löndahl is an Associate Professor at the Department of Design sciences at Lund University. We “sit together” online to discuss his work as well as current questions about SARS-CoV-2 transmission pathways.
Olga Garmash: Hi Jakob! Could you please tell us about your research at Lund University? What are the most pressing questions in your field?
Jakob Löndahl: My research deals with lung-particle interactions and on bioaerosols. One main topic is diagnosis of lung disease and the other is the transmission of disease through inhalation. A focus for several years has been transmission pathways for various infectious diseases. We studied the winter vomiting flu and some respiratory diseases. Now we are looking at the coronavirus, of course, but we work also on other respiratory viruses, such as RS-virus and influenza. Bioaerosol is quite different from my original topic as a PhD student – the link to my present research is primarily inhalation. The PhD topic was aerosol deposition in the lungs and particle effects on the lungs. Later, I investigated if changes in lungs can be measured with aerosols, which they can. We [research group, ed.] developed a method for a diagnosis of the COPD [Chronic Obstructive Pulmonary Disease, ed.] based on nanoparticle aerosols. COPD is the third most common cause of death globally, but it is vastly under-diagnosed. COVID sort of merges all these things. It is a virus that has effects on the lungs, probably long-term effects also, such as increased risk of fibrosis in lungs, which I think would be measurable with aerosols.
O.G.: Is your work more of an experimental work or is it a lot to do with combining experiments and models?
J.L.: I work mostly experimentally. I have done some theoretical work too, but I like experiments most.
O.G.: I heard from colleagues that you have been taking samples of aerosols in the hospital air and testing them for SARS-CoV-2 virus. Could you say something about the research questions and measurements?
J.L.: Yes, we have been sampling aerosolized viruses, bioaerosols, at hospitals for several years. Two of our PhD students have done much of this work, Malin Alsved (who became a PhD on Sep 18) and Sara Thuresson. We carried out measurements at the infection clinics and other places in Lund and Malmö, and were setting it up again in January this year. Then this new virus turned up. Naturally, we started looking for it in our samples, too. In Sweden, we’ve had many patients, so there have been lots of measurement opportunities. However, due to all regulations and safety requirements it has not been easy to take the samples. At the moment we have gathered around 500 air samples from around the corona patients. What we specifically looked for, which is still not investigated, is SARS-CoV-2 from aerosol-generating procedures in health care. It can be expected that these viruses will be in the air, although usually at very low concentrations in relation to the infectious dose. Sometimes the concentrations can be high for various reasons, maybe due to some medical procedures. It is important to identify these procedures because this is when it is most critical to have appropriate breathing protection.
O.G.: So were you mainly measuring the air? Were you measuring in different rooms with patients and rooms with no patients?
J.L.: Yes, we have mainly sampled from air, but have also collected some surface samples. We measured air close to patients, in hospital corridors and in different rooms. We sampled around various types of patients: from very early stages of disease to very severe intensive care patients. Actually, we also measured during the autopsy. We measured it in two dissections. And there are some more activities, which we would like to measure. For instance, women with the coronavirus disease giving birth. We also measured aerosols, droplets and viruses from singing. A study that was published a couple of weeks ago.
O.G.: I assume that there are a lot of challenges associated with the measurements at the hospital. In addition to personal protective equipment, what other challenges did you face in establishing the measurements and sampling?
J.L.: Well, first we have safety. In the very beginning, no one really knew how efficient this virus was in infecting others. We used quite heavy protection, but that part has become easier and more relaxed with time. We generally use the same protection as the health care personnel, which works well. Secondly, SARS-CoV-2 is a dangerous virus, so we can’t easily handle it in the labs. There is a lot of administration around that. The third problem, which is the main problem now, is that all the reagents and chemicals needed to do the analysis are in short supply. Hospitals are the priority, so it has been difficult to do the analysis at the university lab. We can sometimes do the analysis in the hospital lab, but they do not sequence and quantify the viruses as we would ideally wish.
O.G.: You explained also that you measured different locations and different situations in the hospitals. How do you think the measurement location affects your results? Maybe you don’t have the results yet, but what is your opinion?
J.L.: There have been some publications by now, and I think we begin to understand the transmission pathways of the SARS-CoV-2 virus quite well. But still, there are no measurements really of aerosol generating procedures, so it remains to be published. The virus concentrations vary a lot between patients, which is something we’ve been looking more into lately. To get very high aerosol concentrations, you probably have to have patients early in the disease. Someone who’s been sick for weeks would not shed much virus containing aerosols. In addition, concentrations above pathogen invasion threshold are typically only obtained at close range. At long range, the viable virus concentration in aerosol will be low for various reasons. It’s diluted, it’s damaged and it’s deposited.
O.G.: It actually relates to my next question. In your opinion, how much of SARS-CoV-2 virus is transmitted through aerosols? What kind of evidence do scientists need to provide in order for this route to be more accepted by the medical community and by the public?
J.L.: There has been a lot of misunderstanding between the aerosol people and the medical community. I am not sure that the aerosol community has fully understood what airborne transmission means in an infectious disease context. In infection medicine, airborne diseases traditionally mean those that transmit very easily over long ranges such as through ventilation systems or outdoors by wind between people and buildings. A short visit outside a patient would constitute a high risk of infection. Examples are measles, anthrax, smallpox, legionella or even the SARS in 2003. For a virus to be airborne, it has to fulfill a number of criteria such as a very low infectious dose and high persistence to environmental stress. I think SARS-CoV-2 fulfills the criteria to be airborne, but it is not a main route of transmission in the same way as for typical airborne diseases. Environmental persistence is sufficient, although not high, and infectious dose may also be low enough, although in most cases only at close range.
There are different levels of airborne diseases. There are diseases that are so called obligate airborne transmission, which means through the air only. Tuberculosis may be the only communicable disease in this category. Then there are diseases that are preferentially transmitted through the air, such as those previously mentioned. Finally, there are those many diseases with opportunistic airborne transmission. These may transmit through inhalation over a long range when circumstances are favorable, such as when there is a highly infectious person over a long time in an environment with poor ventilation, noise and dry air. They are normally not classified as airborne, as diseases are classified by their main route of transmission. I think COVID-19 is an opportunistic airborne disease in this sense. This is not the main route of transmission as far as I can see it, but it can happen. When it comes to the environmental samples, the highest doses are found on the surfaces and large droplets.
O.G.: Is “aerosol transmission” not an equivalent term to “airborne transmission”?
J.L.: It is tricky. Airborne and aerosol transmission in medicine are used synonymously, so they mean the same thing. Nowadays I say that we study “aerosol and droplet transmission” because a large part of the droplets are also aerosols by the definition we use in aerosol science. In our paper on aerosol emissions from singing1, we chose to define aerosols as particles smaller than 5 µm, as is done in infection medicine due to rather obscure historical reasons. From a physics, or even inhalation, point of view it is a poor choice of cut-off. I think this pandemic will result in a revision of a number of erroneous or outdated ideas that still circulate around aerosols in medicine.
O.G.: Do you think studying particles below 5 µm would be important in terms of transmission and prevention of diseases?
J.L.: I think studying the range below 1 µm is particularly interesting. For instance, it seems that for some diseases a large fraction of the culturable viruses are found in the small end of the size scale. There is just one study so far that has been able to culture SARS-CoV-2 virus from aerosols. They used a method that can sample down to 10 nm. It is a BioSpot instrument, which we also have used for sampling during Covid, but with less success. Often it’s preferable to collect high air volumes of the viruses in a liquid for analysis, but it can be tricky for sub-micron particles.
O.G.: Related to that recently published paper: does shouting or singing, actually, produce more aerosols than normal talk?
J.L.: Yes, loud voicing increases aerosol emissions from the respiratory tract. We showed it and others have shown it too. With singing, and I think we are the first to publish on singing, there are two factors that increase emissions: 1) it is typically rather loud compared to normal talking, and 2) many people in the room may sing at once. In comparison to talking, this can increase the aerosol concentration tenfold or more. Unfortunately, I have to say, as I love singing myself, singing is something that at the moment should be done with precautions and distancing. The emitted large droplets, not the 5 µm droplets, but the very large droplets are depositing quite quickly. Luckily, they can be assumed to contain the most viruses. Some droplets may spread longer distances of course, but they will probably be less likely to transmit the COVID-19 disease due to a decrease in dose and viability.
O.G.: You mentioned earlier that aerosol transmission is not the main route for COVID-19 transmission. In light of discussions that are going on at different workshops and conferences, do you think aerosol scientists are over-interpreting the aerosol transmission route of COVID-19?
J.L.: I am well aware of these discussions and there are different bubbles with risk of group-thinking around this in social media. If you define aerosols as we typically do in aerosol science, with the 100 µm limit, then I think it is aerosol transmission to a large extent. But aerosol transmission in infection medicine is not only about particle sizes and aerodynamics, but also about behavior of the disease. If you say that this is an airborne disease, many in healthcare will think that it is a disease that is transmitted between rooms and through ventilation, and there are almost no examples of that for COVID-19. A dangerous airborne disease means that a space suit is needed for protection and that many healthcare workers would refuse to be in the same building as patients. None of this is necessary other than in special circumstances.
Usually, COVID-19 transmission is occurring at short range. It’s probably not because the droplets are just falling down, which would be a too simplified explanation. With increasing distance from the source, the aerosol concentrations are rapidly decreasing because of the dilution and infectivity decreases due to environmental stress on the virus. Also, it seems that the infectious dose needed for the transmission of this disease is not that low. Therefore, over the longer range, it’s not transmitting very efficiently. However, similar to other diseases with opportunistic airborne transmission I am quite convinced it happens sometimes. But typically, over longer range I think the risk of transmission through other pathways, such as transport of contaminated objects may also be considerable. This makes it behave like a droplet disease. From an aerosol perspective, you may call it “short range aerosol transmission”, but from a medical viewpoint this is a quite contradictory concept. The division between aerosol and droplet transmission is a false dichotomy, but helpful as a simple way of communication around disease transmission in healthcare.
Have you heard about the Pareto distribution or Price’s law? It is interesting in relation to how this disease is transmitted. To explain this phenomenon, I can take an example from science: it’s been shown that a rather small amount of scientists (let’s say 5%) are producing about 50% of all the important discoveries. The reason is that you need a number of things to happen at the same time. You need a clever person, but that is not enough. You also need a good research environment, a relevant topic, proper networks, funding and many other things. When all of these things happen at the same time, you get great research. The Pareto distribution shows that only a small group of people will have all these things at the same time and thus obtain a large research output, while the majority won’t. This small group will do a lot of the important findings. Others will contribute, but probably won’t do Nobel prize winning discoveries.
I think it is a bit similar to COVID-19 disease. Super spreaders often appear when we have a highly infectious person without much symptoms, meeting many people at the peak viral load and, maybe, in an environment with poor ventilation, loud voicing, and long residence times. For most that are sick, this will not happen, but sometimes all these factors come together. Thus, as shown by the Pareto distribution, a small group of people can cause a relatively large part of transmission. In these cases aerosol transmission may sometimes be important. The common way of spread is within families and workplaces, at rather close contact. Also, there are a lot of examples when it is not spreading within families, if you just keep staying in different rooms and are careful with especially hand hygiene. If COVID-19 was a typical airborne disease, this would not happen. It would never be possible to isolate measles in a normal house, with just a closed door. When COVID-19 first appeared, airborne transmission was overstated in many countries because of the original SARS in 2002, which was airborne to a larger extent. Because of that, there were too strict precautions and many people didn’t dare to go to work at hospitals. I think that now we’ve had this disease around for some time and know the risks better. The healthcare personnel do not get the disease by just walking in the corridors or rapidly inhaling the air from the same room as a patient. It is not the way it is spreading.
O.G.: This has been a very interesting discussion. I found your opinions very interesting in comparison to the US community that is ringing the bells to the authorities.
J.L.: This discussion around airborne versus droplet transmission is full of misunderstandings and strong opinions. It will not be solved easily. For influenza, it has been discussed for decades to what extent it is transmitted through aerosols and to what extent through other routes. A review a couple of years ago concluded that aerosol transmission occurs somewhere between half of all cases and very seldom. But it is not never. For COVID-19, we will likely discuss this for many years to come.
O.G.: Of course, SARS-CoV-2 virus has gained a lot of attention among people. Can we take this opportunity to talk to authorities and society about aerosol and droplet transmission of diseases from an aerosol science point of view? Is this being done in any Nordic country that you know of?
J.L.: Yes, absolutely. For example in Sweden, hospital hygiene, infection medicine and clinical microbiology are the medical specialities that primarily discuss how various diseases are transmitted and how we should protect ourselves. I think they have paid a lot of attention also to us aerosol scientists.
So far this year, knowledge has increased a lot about airborne diseases. Interest in airborne transmission began to increase in Sweden a couple of years ago when we discussed winter vomiting flu, which was not considered an airborne disease at the time. I think we are slowly reaching a much more nuanced understanding of infectious aerosols. At least in Sweden, the 5 µm aerosol definition previously used by the medical community is increasingly altered to 100 µm, but probably this will not change so much the basic understanding of transmission routes from droplet to aerosols. There is not a sharp line between these two for various reasons - physical, virological as well as medical.
O.G.: Thank you so much for sharing your research and opinions. Would you like to still add something?
J.L.: When it comes to transmission pathways, I think it is difficult to give a short answer. Maybe a message to the aerosol community could be to try to understand what airborne transmission means for those with a background in infectious disease. I think we also have some things to learn from them. Hopefully, we will reach improved concepts and classifications for transmission pathways in the future.
O.G.: We clearly need more collaboration! Thank you for the interview!
J.L.: Thanks!
The paper referred to is:
M. Alsved, A. Matamis, R. Bohlin, M. Richter, P-E. Bengtsson, C-J. Fraenkel, P. Medstrand & J. Löndahl. (2020). Exhaled respiratory particles during singing and talking, Aerosol Science and Technology. Find it by clicking at either reference.
Find out more about Jakob’s activities and publications at http://www.eat.lth.se/personal/jakob-loendahl/
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