New Studies on Airborne Transmission
During the webinar, Dr. Zuroweste described two recent epidemiological studies that highlight the risks associated with the aerobiology of COVID-19. One research paper covered the resulting COVID-19 infections at different tables in a restaurant where one diner at a center table was COVID-19 positive, called A1. There were four other tables in the vicinity of A1’s table, and a ventilation system along one wall that circulated air across A1’s table and two others. Four of ten of the diners at A1’s table became symptomatic. Of the four diners at the table “downwind” of A1’s table, three of them became infected within a week. Of the seven diners “upwind”, two became infected. Two other tables were not in line with the ventilation system; no diners from those tables became sick with COVID-19. “This shows that, probably, a significant part of this was the airborne component,” Dr. Zuroweste said. While perhaps some sharing of food occurred at A1’s table, the cases at surrounding tables point to airborne transmission, he added.
In a Morbidity and Mortality Weekly Report (MMWR) from the CDC, researchers followed a choir that practiced for 2.5 hours. One COVID-19 positive and symptomatic individual attended choir practice. After the practice, 32 confirmed cases of COVID-19 and 22 probable cases were identified to be related to the symptomatic singer. Three were hospitalized and two died. “Again, there may have been handshaking and hugging, but probably a significant part of this infection rate was airborne,” Dr. Zuroweste concluded.
Read the MMWR: High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice — Skagit County, Washington, March 2020: https://bit.ly/2LW9Hhs
The restaurant example comes from a recent article by Erin Bromage, PhD, a Professor of Biology: “The Risks, Know Them, Avoid Them:” https://bit.ly/2ZEB4EE
By Claire Hutkins Seda, Senior Writer, Migrant Clinicians Network and Managing Editor, Streamline
In mid-May, Migrant Clinicians Network hosted a one-hour webinar with Chad Roy, PhD, a microbiologist and director of the infectious disease aerobiology and biodefense research programs at Tulane University’s National Primate Center, and with Ed Zuroweste, MD, Founding Medical Director at Migrant Clinicians Network. The two presenters responded to a lengthy list of participant questions around new COVID-19 findings from the growing data that researchers are amassing regarding the airborne infectiousness of the virus. But both were clear: as the virus spreads, we gather more data, and these data combined with increased understanding from newly conducted experiments lead to a more refined understanding of COVID-19, its spread, and the best ways to reduce the spread.
“Everything is moving so quickly – and this is the best we know today,” advanced Dr. Zuroweste. To demonstrate the rapid changes in our understanding, Dr. Roy added, consider scientists’ understanding of the aerobiology of COVID-19. Initially, there was little evidence of the aerosol efficiency of COVID-19, the ability for aerosolized particles with the virus to maintain themselves in the air. Early recommendations from the Centers for Disease Control and Prevention (CDC) did not recommend masks, due to the lack of data to demonstrate the need for masks among the general population to prevent the inhalation of aerosolized particles with the virus, and perhaps also with the goal to reserve limited supplies of masks for health care workers. Then, new research published in the New England Journal of Medicine found that aerosolized particles retained infectivity for three hours. This was followed by initial research that a significant number of infected individuals – perhaps 40 to 50 percent of total cases – never become symptomatic.1
“Even in those who do become symptomatic, for the first two to four days, they are not symptomatic, yet they can spread it,” noted Dr. Zuroweste. These new understandings of the virus prompted new CDC recommendations on face masks among the general population. Masks of any kind, including surgical masks, homemade masks, or any type of cloth barrier, will impede big droplets expelled from the mouth to enter the air. This reduces the spread of COVID-19 from asymptomatic but infected individuals to those around them. However, the research needs to catch up to quantify how much it protects mask-wearers from inhaling aerosolized particles with COVID-19. “Surgical masks, face masks – they do an incredible job of protecting others from transmission, but not vice-versa, necessarily,” Dr. Roy said. This confusion over mask effectivity – that they protect others from the mask-wearer, but they provide unknown protection for the mask-wearer – is further complicated by N-95 respirators. N-95 respirators are utilized by health care workers who work with COVID-19 cases, where the providers require a high level of protection for themselves. “Ninety-five percent of these tiny particles are not going to permeate [the N-95 respirator],” Dr. Zuroweste said, as long as the fit is correct. “[Health care workers] have to be fit tested to make sure they form a seal on your face.” Such respirators, which remain in short supply, are less critical for the general public, who are not working in close proximity with infectious patients.
Our understanding of the aerobiology of COVID-19 continues to evolve. Dr. Roy’s research has contributed to our growing knowledge. “[The conclusion of initial research in the New England Journal of Medicine] wasn’t because [researchers] had determined that at three hours, the infectivity was gone; it’s just that they had done that experiment for three hours,” and then concluded the research, explained Dr. Roy. He and his colleagues replicated the experiment. “We felt it obvious to extend those time periods [until] the aerosol infectivity drops off… kind of like an [infectivity] half-life.”
“At 16 hours, there was still an infective fraction of the virus in those aerosols,” Dr. Roy continued. “I’ve worked with a number of viruses in my career, doing the same types of experiments. In influenza, for example, we don’t see that – we see it decay in a couple of hours.” Initial findings, currently under peer review for publication, are accessible for pre-publication view.
Dr. Roy’s research, that COVID-19 viruses can be found in aerosolized particles for up to 16 hours after expression, significantly changes our understanding of the virus, yet not all aerosolized particles will remain active in the air for such a long period of time. The research was conducted in a dark chamber, under ideal temperature and humidity for the virus. Dr. Roy says that his colleagues are presently completing chamber research on the virus that exposes the aerosolized particles to ultraviolet light, similar to that from the sun. They found COVID-19’s aerosol efficiency with exposure to UV light dropped from 16 hours to a minute and a half. “It’s highly susceptible to light,” Dr. Roy said. “It’s all a matter of context.”
Similarly, temperature and humidity may play a role in the decay of the virus. Outdoor workers, including agricultural workers and outreach workers providing education to agricultural workers, can take advantage of wind, light, and warm days. Many worker health advocates are focusing heavily on ventilation, which may be the key adjustment to reduce indoor workplace spread of COVID-19, including for agricultural worker housing and transportation.
The frustrations, the misinformation, and the exhaustion are in part because the research is only beginning to be gathered, and it takes time for the public health authorities to translate the research into action. Drs. Roy and Zuroweste ask health advocates to remain vigilant and stay informed as new data are released. COVID-19 is new, and consequently, it takes time for researchers like Dr. Roy to gather data, analyze findings, and write up their conclusions. Research is then followed by peer review and publication, which in turn finally influences public health decisions. “As this develops, and as we learn more about this, it can really inform about transmission, and mask use, the [other] engineering controls to protect yourself against the virus.”
Here are the questions that participants asked during the webinar, answered by Drs. Roy and Zuroweste.
What is the probability of transmission outdoors?
“It’s highly susceptible to light,” Dr. Roy said, as new research is beginning to indicate.2,3 When outside, “you’re in millions of cubic meters of air, so the dilution effect on these particles – I was working with highly concentrated particles – is massive,” when outside. “Remember, it takes probably more than one virus particle to induce infection. There’s a multiplicity of viral particles that you’re exposed to in order to become infected,” he added, although the dose of aerosolized particles needed for infection is still unclear.4 The dilution, aided with early research on sunlight, point to a reduced risk of transmission outdoors, as long as distance is maintained. “It depends on the situation, and considering all the environmental factors,” he added.
I am an Outreach Worker with a pre-existing lung disease. What is the best practice to protect myself in the labor camps and confined workspaces in the health center?
In addition to keeping sufficient physical distance and wearing a mask, “if you have a pre-existing condition at a labor camp, if you’re interacting with farmworkers, I would have the wind at your back. This is something we learned from tuberculosis a long time ago. If I can be outside, interviewing people with the wind at my back, going toward them, I feel much safer,” Dr. Zuroweste answered, again, alluding to the importance of good ventilation to reduce virus transmission. He also recommended an N-95 respirator for maximum protection for an enclosed space.5
Are cloth face coverings helpful at all?
“If I happen to have COVID myself and I’m talking, [which] would expel [the virus], if I have anything covering my nose and mouth, I would assume that part of that, especially the big droplets, would be impeded by the mask,” Dr. Zuroweste said. A meta-analysis in The Lancet confirmed that masks were beneficial in impeding droplets.6 “It would help the person who’s wearing it, not to spread [the virus] as much.” Dr. Roy added that cloth and surgical masks do not protect from viruses flowing around the edges as a mask-wearer breathes in. Only N-95 respirators that are fit-tested to the wearer can protect the mask-wearer from inhaling particles that may contain the virus, which is why N-95 respirators are better protection for any health care worker who may be working with COVID-19 positive patients.7
What do you recommend for farmworkers who need to be transported to and from work in buses or vans? Should they wear masks, and what about the staff who drive these workers?
“If anybody is sick – any symptoms at all of COVID – they shouldn’t get in the van,” Dr. Zuroweste said. Additionally, all windows should be kept open to maximize ventilation, and all riders, including the driver, should don a mask. Distance should be maintained by increasing the number of vehicles and frequency of trips. The CDC’s interim guidance provides more specific “special considerations” for shared transportation: https://bit.ly/2Ve3faL.
You talked about ventilation in the vans – that's one type of engineering control. What kind of engineering controls can we use in a clinical setting, in a closed space?
“This virus, as well as rhinoviruses, noroviruses, and other viruses that cause illness that are transmitted in the air are highly susceptible...to UV,” Dr. Roy said, noting that the data around UV and COVID-19 is still preliminary.8,9 “When we stay out of enclosed areas, or ventilate in enclosed spaces, and get into the light, or... increase circulation, then it will further reduce the possibility of us coming in contact with the multiplicity of viruses that it probably takes to infect us.” Opening a window or getting into the sunlight are “practical solutions we all can do,” he added. “This virus is not Superman – it is susceptible to all those things.” In an enclosed space in which these controls are not possible, respiratory protection is necessary, and proper ventilation remains key.10
Additional Participant Questions
The participants of the webinar had additional questions that Drs. Roy and Zuroweste were unable to answer in the limited time provided. Here are some of the additional questions posed by participants, answered by MCN’s environmental and occupational health team.
Should we rethink our PPE program? Should all employees wear respirators?
The determination of who should use respiratory protection is made after the employer conducts an appropriate risk analysis. In some cases, this may mean expanding or establishing a respiratory protection program. For those employees whose risk is high or very high and whose risk cannot be eliminated or significantly decreased by engineering controls, the use of personal protective equipment such as respirators is recommended. OSHA and the CDC have generated various guidelines to assist in risk classification and determination of controls to be used:
CDC’s COVID-19 Businesses and Workplaces: https://bit.ly/3en1mj3
OSHA’s COVID-19 Standards: https://bit.ly/3d1EJAd
What are the differences between surgical masks and respirators?
Surgical masks and respirators, like N95 or N99, differ mainly in the intention of protection and their efficiency. On one hand, face masks (including surgical masks and homemade masks) are intended to protect the people around who wears it, while respirators protect the individual who is wearing it. On the other hand, their filtration efficacy when tested using NIOSH methods, could be less than 70 percent for a facemask and as high as 99 percent for respirators. More information regarding the differences between facemasks and respirators like the N95 masks can be found here:
3M’s Respirators and Surgical Masks: A Comparison: https://bit.ly/3gikC33
FDA’s N95 Respirators and Surgical Masks (Face Masks): https://bit.ly/2X46z9H
Are all respirators the same? There seems to be more KN95 respirators available than N95.
There are several types of respirators available; however, not all are certified by NIOSH or accepted by OSHA. Typically, in the US, a respirator must be NIOSH approved in order to be used as respiratory protection. However, due to the COVID-19 emergency, OSHA is allowing the use of some non-NIOSH approved respirators, like KN95 or PFF, that are certified using standards from non-US jurisdictions.
OSHA’s Enforcement Memo: https://bit.ly/3gkOBao
NIOSH’s Understanding the Use of Imported Non-NIOSH-Approved Respirators: https://bit.ly/3bZAdkn
CDC’s Interim Guidance for Conserving and Extending Filtering Facepiece Respirator Supply in Non-Healthcare Sectors: https://bit.ly/36thNHP
What adjustments can we make to ventilation systems?
Modifications in ventilation systems are an engineering control to protect workers from COVID-19 that would probably lower the pressure on PPE inventory. However, this is currently a field in development. The following organizations are leading the research on ventilation system effectivity. Please watch their updates on COVID-19 for new information, resources, and tools.
American Industrial Hygiene Association’s COVID-19 Resources: https://bit.ly/3c94Y6R
American Conference of Governmental Industrial Hygienists: https://www.acgih.org/coronavirus
American Society of Heating, Refrigerating and Air-Conditioning Engineers: https://bit.ly/2A4suo2
1 Oran DP, Topol EJ. Prevalence of Asymptomatic SARS-CoV-2 Infection: A Narrative Review [published online ahead of print, 2020 Jun 3]. Ann Intern Med. 2020;M20-3012. doi:10.7326/M20-3012
2 Sagripanti JL, Lytle CD. Estimated Inactivation of Coronaviruses by Solar Radiation With Special Reference to COVID-19 [published online ahead of print, 2020 Jun 5]. Photochem Photobiol. 2020;10.1111/php.13293. doi:10.1111/php.13293
3 Ratnesar-Shumate S, Williams G, Green B, et al. Simulated Sunlight Rapidly Inactivates SARS-CoV-2 on Surfaces [published online ahead of print, 2020 May 20]. J Infect Dis. 2020;jiaa274.doi:10.1093/infdis/jiaa274
4 Somsen GA, van Rijn C, Kooij S, Bem RA, Bonn D. Small droplet aerosols in poorly ventilated spaces and SARS-CoV-2 transmission [published online ahead of print, 2020 May 27]. Lancet Respir Med. 2020;S2213-2600(20)30245-9. doi:10.1016/S2213-2600(20)30245-9
5 Chu DK, Akl EA, Duda S, et al. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. The Lancet. 2020. doi:10.1016/s0140-6736(20)31142-9
6 Grinshpun SA, Haruta H, Eninger RM, Reponen T, McKay RT, Lee SA. Performance of an N95 filtering facepiece particulate respirator and a surgical mask during human breathing: two pathways for particle penetration. J Occup Environ Hyg. 2009;6(10):593-603. doi:10.1080/15459620903120086
7 Sagripanti JL, Lytle CD. Estimated Inactivation of Coronaviruses by Solar Radiation With Special Reference to COVID-19 [published online ahead of print, 2020 Jun 5]. Photochem Photobiol. 2020;10.1111/php.13293. doi:10.1111/php.13293
8 Azimi P, Stephens B. HVAC filtration for controlling infectious airborne disease transmission in indoor environments: Predicting risk reductions and operational costs. Build Environ. 2013;70:150-160. doi:10.1016/j.buildenv.2013.08.025
Watch the MCN webinar with Dr. Chad Roy and Dr. Ed Zuroweste: https://bit.ly/3gpt0xD
Access Dr. Chad Roy and colleagues’ research in this pre-publication article: Comparative dynamic aerosol efficiencies of three emergent coronaviruses and the unusual persistence of SARS-CoV-2 in aerosol suspensions: https://bit.ly/3d6UENN
Dr. Zuroweste recommends an article by Erin Bromage, PhD, a Professor of Biology, on the airborne component of COVID-19: “The Risks, Know Them, Avoid Them:” https://bit.ly/2ZEB4EE
This article is available on MCN’s blog in English and Spanish: https://bit.ly/3fFI6Ou
Additional Resources by Topic:
You can access this complete list of resources with links by visiting: https://bit.ly/2X6EFtH
On Masks and Respirators:
Respiratory Protection During the COVID-19 Pandemic: Best Practices for the Agricultural Community, from Colorado State University’s High Plains Intermountain Center for Agricultural Health and Safety: https://bit.ly/3gp8bSX
NIOSH 's Guide to Air-Purifying Respirators: https://bit.ly/2ZBEgRm
CDC’s infographic on surgical masks versus N95 respirators: https://bit.ly/3d3uifE
Johns Hopkins Bloomberg School of Public Health’s “Can a Mask Protect Me?” video: https://bit.ly/2TBr3ED
OSHA’s COVID-19 poster, Steps to Correctly Wear a Respirator at Work: https://bit.ly/3em0gEi
Minnesota Department of Health’s Youtube video, “Donning and Doffing Facial Protection – Mask alone”: https://youtu.be/OABvzu9e-hw
On Minimizing Risks:
CDC’s Interim Guidance for Agricultural Workers and Employers: https://bit.ly/2Na5FCH
CDC’s Interim Guidance for Businesses and Employers Responding to Coronavirus Disease 2019: https://bit.ly/3gl3oSu
Read this article in the Summer 2020 issue of Streamline here!
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