“How can airborne transmission of COVID-19 indoors be minimized”/Environment International

Could the SARS-CoV-2 virus become the secondhand smoke of the 2020s?

Remember how smokers got kicked to the curb because of the difficulty of designing ventilation systems that kept the cigarette smoke of the “smoking section” from permeating entire bars and restaurants?

Now studies are implicating inadequate ventilation in the spread of SARS-CoV-2 in buildings in both China and the U.S.  SARS-CoV-2 is the virus that causes the deadly, pandemic disease COVID-19.

Chinese scientists who studied 381 COVID-19 outbreaks which infected 1,245 people in 120 cities in April found that all but two infections happened indoors, and they warned that China’s “required ventilation rate is only 3 to 9 liters per second (L/s) per person in shopping malls and 2 to 8 L/s per person in public buses, whereas a ventilation rate of 8 to 10 L/s per person is required for good indoor air quality. An international systematic review showed that a rate as high as 25 L/s per person may be needed.”

The Chinese study at MedRxiv has yet to be peer-reviewed. The same is true of another published Monday involving a now somewhat notorious COVID-19 outbreak in Washington state. But the evidence indicating problems with infections from invisible, free-floating SARS-CoV-2 is growing.

It comes at a time when businesses are reopening across the country and the number of reported COVID-19 cases is again creeping upward.  Southern and Western states – Florida, Arizona, Alabama, and Texas – are now witnessing record numbers of daily Covid-19 cases, Inc. reported.

Temperatures are now high in all of those states often pushing people toward the comfort of air-conditioned buildings where air circulation may be poor.

In the Washington case, 53 of 61 members of a church choir came down with the disease after a rehearsal ina building with a suspect air circulation system. Two eventually died.

Singing in the COVID

 A follow-up study of that COVID-19 cluster was conducted by scientists from the universities of Colorado, California and Virginia Tech, the United Kingdom’s National Health Service, the universities of Leads and Queensland in the UK along with researchers from the Netherlands, Scotland and Estonia. They concluded that in the confined, poorly ventilated environment of a “fellowship hall” in Mount Vernon, Wash., one person ill with COVID-19 was able to pump enough viruses into the area to infect most of the rest of the Skagit Valley Chorale.

The infections happened even though the Chorale practiced social distancing, the researchers said. They suggested the widespread infections among the dispersed members of the group argued against “close contact” spread by touching or respiratory droplets.

“At the time of the chorale rehearsal on 10 March 2020, because of emerging concern about SARS-CoV-2, person-to-person contact and touching of surfaces was consciously limited,” they wrote.

“The risk of widespread transmission owing to close contact would seem to be low in this event, considering that there is believed to have been only one index case who would have been seated in proximity to only a small proportion of the other chorale members. If transmission by close contact and/or fomites (contaminated objects) were indeed the dominant modes of transmission, then the secondary attack rate should have been much smaller than the observed range of 53 (people or) 87 percent.

“We would also expect to see the secondary cases predominantly among those in closer proximity to the index case rather than distributed broadly throughout the room. Given the circumstances of the rehearsal, such a high secondary attack rate by the close-contact route would have necessitated effective transmission based largely on brief proximate encounters. That interpretation of the high attack rate in this event seems much less probable than the alternative explanation, i.e. that inhalation of infectious respiratory aerosol from ‘shared air’ was the leading mode of transmission.”

Whether face coverings would have helped is an unknown, but studies of the hospital rooms of COVID-19 patients would indicate that although masks block droplets, the virus still manages to make its escape into the surrounding environment.

A correspondence scheduled for publication in Environmental International in September notes that examinations of the rooms of people hospitalized with COVID-19 have found SARS-CoV-2 viruses all over the place – including in the air – and argues that “it is scientifically incongruous that the level of evidence required to demonstrate airborne transmission is so much higher than for these other transmission modes.”

“The infectious agents of several other diseases (tuberculosis, measles, chickenpox) are recognized to be transmissible via the airborne route, either by the short-range (face-to-face, conversational exposure) or by longer-range aerosols.”

That report compiled by scientists from Australia, the United Kingdom, the Netherlands, the U.S., Italy, Sweden, Estonia, Denmark, Spain, Singapore, Finland, Japan and Canada says building ventilation and occupancy are being badly overlooked as pandemic problems.

Blowin’ through the mask?

Writing in the Journal of Fluid Mechanics, John Hopkins University scientists have also raised questions about the efficacy of masks and suggested more study is badly needed.

‘The outward protection afforded by face masks has emerged as a particularly important issue in the COVID-19 pandemic because a SARS-CoV-2 transmission may occur early in the course of infection, not only from symptomatic patients but also from asymptomatic as well as minimally symptomatic patients,” they wrote. “Indeed, the late switch to recommending universal use of face masks in the was based on the recognition that this spread by asymptomatic hosts might be a significant driver of COVID-19 infections.”

The issue, they address is whether masks actually reduce viral loads in indoor environments where most infections are taking place.

“While a mask can significantly reduce the velocity of the throughflow jet during expiratory events, the increased pressure in the region between the mask and the face pushes the face mask outwards, resulting in increased perimeter leakage,” they write. “The leakage jets that issue from the perimeter can be turbulent and highly directed, potentially serving as effective dispersers of respiratory aerosols in transverse directions.”

Coughing and sneezing only up the ante, they said, which adds to the “critical need for modeling, flow-induced billowing and associated leakage enhancement during expiratory events. Ultimately, analysis should not only enable a detailed evaluation of the protective efficiency of face masks; it should also drive design changes that enhance mask performance and provide data that inform guidelines on practices such as social distancing.”

Given the likelihood SARS-CoV-2 virus are likely to be found floating around and possibly concentrating inside poorly ventilated buildings whether people are wearing masks or not, the scientists writing in Environment International argue that there needs to be more focus on ventilation in “indoor environments, because this is where most transmission occurs. Further, the measures mostly apply to public buildings. In residential houses and apartments, normal practices (e.g. segregating infected individuals, opening windows and doors, and using portable air-cleaning devices when practical) to ensure healthy indoor air, should stay in place at any moment.”

Opening windows and doors to increase ventilation has been known to be protective since the Spanish flu swept the globe more than a century ago, but many buildings are now designed with windows that don’t open.

Five steps

But even where that is the case, much can be done to improve building safety, according to the scientists who laid out a five-step plan.

1. Ventilation should be recognized as a means to reduce airborne transmission. Most hospitals have already taken this into account, they noted, but in most offices, businesses and public buildings, “ventilation rates are significantly lower than in hospitals for various reasons, including limiting airflows for energy and cost savings.”
2. Ventilation rates should be increased by system modifications, be they simple – such as opening the windows – or more complicated, as in adjusting heating, ventilation and air-conditioning (HVAC) systems to pull more fresh air into buildings. This does not come without problems. “For naturally ventilated public buildings, particularly in cold climates….It may be necessary to provide additional heating in some buildings to maintain thermal comfort, particularly where the occupants are vulnerable.”
3. Avoid air recirculation. “The recirculation of air is a measure for saving energy, but care must be taken, as it can transport airborne contaminants (including infectious viruses) from one space and distribute them to other spaces connected to the same system, potentially increasing the risk of airborne infection in areas that otherwise would not have been contaminated.” One Chinese study has suggested an air conditioning unit might have been involved in circulating SARS-CoV-2 in a restaurant there.
4. “Air cleaning and disinfection devices may be beneficial.  In environments where it is difficult to improve ventilation, the addition of local air cleaning or disinfection devices, such as germicidal ultraviolet may offer benefits.”
5. “Minimize the number of people within the same indoor environment in an epidemic.”

The study offers no numbers for minimization because there are no universally agreed upon numbers other than those for social distancing, which might not or might not cut the density down enough.

“Although the physical distance required to avoid transmission through direct contact dictates the requirements for the floor area per person, the rate of ventilation provided and the efficiency of ventilation are the parameters that control the concentration of virus-laden microdroplets in the air exhaled by the occupants and will guide decisions on safe occupancy numbers,” the authors write. “In a school or a supermarket, for example, if the number of infected students or shoppers is low, and the ventilation rate is high, the risk of airborne transmission can be low. Similarly, during an epidemic, reducing the number of people using public or private transport at the same time, e.g. in subway train systems or busses, is part of effective social distancing.”

Public transportation – a climate-change rage before the pandemic – has been taking a beating since the pandemic began. As much as possible, people have shifted to working from home, or traveling to work by means other than public transport if possible when working from offices.

How safe those offices remains a question. The Environment International story would suggest they are not all that safe, but could be made much better.

“If implemented correctly, these recommended building-related measures will lower the overall environmental concentrations of airborne pathogens and thus will reduce the spread of infection by the airborne route,” it says. “Together with other guidance on minimizing the risk of contact and droplet transmission (through hand-washing, cleaning of hand-touch sites, and the appropriate use of PPE), these ventilation-related interventions will reduce the airborne infection rates not just for SARS-CoV-2 in the current COVID-19 pandemic, but also for other airborne infectious agents.”

All of this has been known for decades, but much of it has been avoided as the world has focused on making buildings more energy-efficient.

As the Environmental Protection Agency noted a decade ago, long before COVID-19, “there is significant political and institutional momentum toward energy conservation in buildings which has led to building codes devoted solely to energy conservation and resulted in the tightening of building envelopes and reduced air infiltration and leakage. With air exchange significantly reduced, there is little room for error in protecting indoor air quality.”

SARS-CoV-2 is now shining a bright light on indoor air quality.

On an individual level, the most you can do is protect yourself. If a space looks or feels like it would have once performed well as a smoke-filled bar, the studies suggest it would be best to avoid it.

This is a revised version of the original story. It was updated on June 18 to reflect the national increase in COVID-19 cases.