Proceedings of a Workshop—in Brief

Management of Indoor Air and Airborne Pathogens

Proceedings of a Workshop Series—in Brief

INTRODUCTION

In the United States, people spend nearly all their time indoors, where they are exposed to various contaminants and pollutants that may be present at different concentrations than in outdoor settings. The presence of virus particles and other contaminants provides unique challenges in indoor air environments, particularly if these contaminants can infect people through respiratory routes. These challenges were emphasized during the COVID-19 pandemic because of the documented human transmission of SARS-CoV-2 through the air,¹ but they also apply to other airborne pathogens. Therefore, the Environmental Health Matters Initiative (EHMI) of the National Academies of Sciences, Engineering, and Medicine held a three-part series on Indoor Air Management of Airborne Pathogens to a) consider the state of knowledge about building management, ventilation, and air cleaning for respiratory airborne pathogens; b) discuss experiences with management of indoor spaces during the COVID-19 pandemic, specifically of schools and public transportation; and c) suggest mitigation strategies to be adopted to make these spaces safer. The full statement of task can be found on the project website.² To address these and other related questions, an interdisciplinary group of experts, including natural and social sciences, facilities managers, ventilation engineers, and representatives from affected populations, were invited to share their knowledge and experiences to understand advances and good practices in indoor air management (August 12, 2022) and their uses and associated challenges in schools (September 12, 2022) and public transit environments (November 16, 2022).

This Proceedings of a Workshop Series–in Brief summarizes key themes discussed by participants from the entire series, highlighting specific equipment and approaches that may be effective in reducing indoor infection of airborne pathogens and specific considerations of schools and public transit. The workshop rapporteurs prepared this Proceedings as a factual summary of what occurred at the workshop. The views contained in the proceedings are those of individual workshop participants. Additional details can be found in materials and videos available online.³ This

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Proceedings highlights potential opportunities for action, but these should not be viewed as consensus conclusions or recommendations of the National Academies.

CONTEXT

Throughout the workshop series, speakers and panelists highlighted several approaches that different actors at different resource levels may consider to reduce the risk of infectious particles in the air, based on experimental and modeling studies and experience in either facilities (e.g., school buildings) or public transportation (i.e., buses, trains, and subways). They also highlighted challenges to the implementation of approaches for improving air quality, including costs and burdens of retrofitting existing buildings and public transit vehicles, trade-offs of improving air quality with energy efficiency, unequal access to resources, absence of standards that effectively address airborne pathogen and other contaminants, communication, and the importance of a multidisciplinary teams and systems approach. These challenges recurred throughout the workshop discussions and are woven into the key themes described below.

MAJOR TAKEAWAYS FROM THE THREE WORKSHOPS

A layered and integrated approach to reduce the transmission of airborne infectious particles

Several speakers and panelists throughout the three workshops described the importance of considering complementary engineering and behavioral measures, such as ventilation, filtration, and masking, to control the sources of exposure and reduce the transmission of infectious diseases. Ventilation is defined as supplying or removing air from a space to control air contaminant levels, humidity, or temperature.⁴ Filtration is the removal of contaminants or infectious particles from an environment. Masking is using face masks to limit the number of infectious particles released from people through breathing, speaking, singing, or other behaviors. Shelly Miller, University of Colorado Boulder, and several other speakers stated that good ventilation and filtration can reduce environmental aerosols. Low ventilation is associated with high amounts of viral particles, and high-efficiency particulate air (HEPA) filters lower the number of viral particles in the air. She further stated that the use of air cleaning methods (i.e., methods for removing contaminants in the air) needs to be appropriate for the size of the space. Speakers stressed the importance of measures in reducing the risk of the spread of any airborne pathogens, not only SARS-CoV-2, were aided by the increased knowledge gained during the COVID-19 pandemic.

Several speakers highlighted that the effectiveness of these approaches tends to be determined in controlled, experimental settings, which often do not reflect real-world conditions. Specifically, they noted that the variability in the age, design, and occupancy in various buildings and vehicles, along with resources and training levels, lead to variable effectiveness and use of different ventilation and filtration measures. In addition, Don Milton (University of Maryland, College Park) stated that the first step in reducing airborne infection is managing engineering controls, the next step is administrative changes, and the last step would be individual behavioral changes, such as masking. Engineering controls that are automatic and shield people from airborne hazards are easier to implement than group and individual behavioral controls.

Some speakers said that improving indoor air quality management of airborne pathogens relies on systems-level approaches that (a) incorporate both engineering and behavioral measures, (b) provide clear standards for ventilation and filtration, (c) enable individuals to evaluate the design of their buildings for infection resilience, (d) provide education on effective measures for reducing airborne particles of virus; and (e) equip individuals and managers with the knowledge and technologies they need. These will allow them to assess and understand the risks in their indoor spaces and decide on effective measures for improving ventilation and filtration in those spaces. Some speakers also stressed that achieving action can be difficult, and individuals are often left responsible for implementing guidelines. However, they suggested that highlighting the co-benefits of improving ventilation, filtration, and air cleaning could help push toward action. These co-benefits include reductions in particulate matter and volatile organic compounds from the air, which can also improve health performance, productivity, economic gains, education, and quality of life.

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Acknowledging health inequities and applying strategies to improve air quality

The issue of improving air quality and reducing airborne transmission is a matter of improving public health and ensuring health equity. This is a critical issue, especially when considering populations that have been disproportionately impacted, noted Sandra Crouse Quinn (University of Maryland). Several speakers shared that overwhelming public health data shows that Latino and Black populations have been and continue to be at higher risks of infections, morbidity, and mortality.⁵ Peg Seminario (American Federation of Labor and Congress of Industrial Organizations) noted, one reason is that workers from these populations are the most exposed, yet have the least amount of control over their environments. Many examples of facilities and public transit environments are primarily staffed by minority workers where the relationship between labor and management may be inadequate, with limited trust between the two entities.

Investing in and operating public transportation systems reliably and safely can be a strategy to improve health equity. Similar to many public transportation systems in the United States, the Southeastern Pennsylvania Transportation Authority (SEPTA) is ridden by a higher percentage of people of color, seniors, and low-income people, compared to the local population. The New York Metropolitan Transportation Authority (MTA) employs about 40,000 transit workers, the largest U.S. transit workforce. Early in the pandemic, MTA employees were thrust into the role of frontline workers as they continued operating buses and trains even when the city temporarily closed schools, workplaces, and businesses. Robyn Gershon, NYU School of Public Health, reached out through an existing communication lane with Transport Workers Union (TWU) 100 to measure how transit workers felt about their workplace safety.

STATE OF KNOWLEDGE ABOUT AIRBORNE INFECTIOUS DISEASE TRANSMISSION AND CONTROLS

Microbiological knowledge and considerations for decision-making

Implementing measures based on other known pathogens can sometimes lead to misplaced resources and efforts. Several speakers supported the importance of timely and accurate information about infectious agents and their modes of transmission for determining the appropriate measures for cleaning contaminated spaces. For instance, a few speakers stressed that guidance early on during the COVID-19 pandemic supported cleaning of surfaces to reduce concerns about viral spread through fomites,⁶ and for no mask use for the general population. The guidance changed as more informed knowledge and facts were generated about how SARS-CoV-2 was largely transmitted via aerosol rather than droplets and fomites. Although, speakers of the transportation workshop stated that highly visible measures, such as surface cleaning, continue to enhance rider and worker perceptions of risk. Speakers also referenced the variability in mask-wearing, which, whether through noncompliance with mask mandates or local government policies lifting (or not issuing) these mandates ultimately affected the infection rates in certain cities and led to increased risk of spread via public transportation and other venues.

Milton discussed the relationship between the amount of virus in a person’s saliva (viral load) and the amount of virus released from their breath. In fact, Milton stated that detecting SARS-CoV-2 infection is three times more likely from saliva samples than in nasal swabs during the early days of infection.⁷ For Influenza, seasonal coronaviruses, and SARS-CoV-2, he explained that studies show surgical masks can reduce the amount of fine aerosol particles of the virus in the air by about half and coarse viral particles by nearly three-quarters. Masking prevents many particles from escaping into the air after an infected individual breathes, and it prevents non-infected individuals from exposure to these aerosols, said William Lindsley (National Institute for Occupational Safety and Health/Centers for Disease Control and Prevention). However, Milton said that surgical masks for professional workers are inadequate to prevent SARSCoV-2 aerosol transmission and that effective Personal Protective Equipment (PPE) is warranted in these cases.

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Several speakers shared that the number of people (i.e., occupancy) and their rate of viral shedding contribute to the risk of exposure to airborne viral particles. As the number of people increases, so does the probability of viral shedding, which is a critical factor in assessing risk. Malin Alsved (Lund University) also suggested that fewer viral particles are shed during breathing than speaking or singing, and other speakers suggested that well-fitting respirator (N95) masks can effectively control viral shedding in the air. One critical point about the risk of infection that speakers highlighted is that different pathogens have different infectious doses (i.e., the amount of virus that could result in infection), highlighting the importance of using microbiological characteristics to inform effective ventilation and filtration methods.

Air circulation and air exchanges within indoor spaces

Selected speakers presented important air circulation and exchange details that may contribute to proper ventilation and filtration. For example, it was suggested that including outdoor air during the ventilation process can improve air quality and reduce the number of infectious particles in a building. This is as simple as “opening a window,” noted Catherine Noakes (University of Leeds). However, not all indoor spaces allow outdoor air to be introduced into the airflow. In this case, other engineering and behavioral controls available can be utilized (see sections below). Furthermore, contamination of outdoor air, for example, in the case of high levels of particulates from wildfire smoke, significantly reduces the benefits of introducing outdoor air. Six air exchanges per hour (ACH) is considered the minimum optimal level by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) guidance for indoor air quality.⁸ This frequency in ACH among different building types and even within a building, can vary drastically, detailed multiple speakers and panelists. Paula Olsiewski (Johns Hopkins Center for Health Security) defined air change per hour as “the number of times in an hour that the air volume is supplied,” whether through outdoor air or air pushed through a filter. In addition, high ACH can be confounded by high occupant density, as introduced by Yuguo Li (University of Hong Kong). Schools with adequate and effective ACH are a minority of the cases, pointed out Mark Hernandez (University of Colorado Boulder), who studied the effectiveness of flexible engineering controls that supplement ventilation with high-efficiency filtration. He noted that “while engineering controls can work, it doesn’t mean they do work” and that, while essential, monitoring air quality is just a fraction of capital cost, improvements, and performance.

Natural ventilation is defined as the air flow between the inside and outside of indoor spaces. Shelly Miller provided some examples of natural ventilation, such as normal exhausts, where air is released through ventilation ducts. She said that these systems can use temperature to facilitate the flow of air in and out of buildings, a phenomenon she called a reverse stack effect. Ventilation systems may need to be adapted for improving indoor air quality. For example, Miller shared a case study in Seoul, South Korea, where multiple people contracted COVID-19 due to air transmission between apartments connected by a natural ventilation duct system. The system was designed for airflow within each apartment to leave through the bathroom duct, up an empty shaft, and exit outdoors. However, transmission can occur if airflow reverses depending on indoor and outdoor air temperatures, including methods that pull air with viral particles into apartments, like turning on the kitchen exhaust and opening a window. In this case, a solution might be to install a bathroom fan and duct cover to block reverse airflow.

Olsiewski said the air change rate in naturally ventilated homes is about 1 ACH, in hospitals is 6-12 ACH, and for schools typically is 2-3 ACH. The air change rate among public transit systems varied, with the Washington, DC Metro system having relatively high rates at 15-20 ACH, said Kit Conway (Washington Metropolitan Area Transit Authority [WMATA]). However, even with a high air change rate, the degree of crowding in a specific space (i.e., occupant density) will increase the amount and rate of infectious aerosol released into this space and, therefore, will affect ventilation rates per person, which

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as a result may become less effective than in a low-density setting. For example, if occupancy in an area is high, the ventilation rate may be low even though the air is exchanged at a very high rate.

For schools, starting with assessing and maintaining existing ventilation and filtration systems, such as checking that filters are clean, flow rates are set correctly, and outdoor air can be introduced, is a necessary first step to improving air quality, said Noakes. Olsiewski noted that many schools had poor ventilation before the pandemic (e.g., 41% have poor heating, ventilation, and air conditioning [HVAC] systems).⁹ She said that the effectiveness of ventilation measures employed in schools is difficult to glean because existing studies have highly variable data collection methodologies to study the reduction of infection risk that considers diverse behavioral and environmental factors. Examples of potential solutions that could help schools are upgrading their systems by using commercial UVC devices for inactivating viral particles safely, or creating a DIY (do-it-yourself) version of air filters to remove viral particles from the air.

Characteristics and proper use of ventilation systems

Ventilation systems are designed as either natural or mechanical systems. Mechanical ventilation is equipment that circulates fresh air, outdoor air or partly reused air, through ducts and fans. Several participants explained that a higher ventilation rate reduces the transmission of airborne pathogens in buildings, including in schools and public transportation settings.

Andrew Persily (National Institute of Standards and Technology [NIST]) discussed good practices for ventilation management. These practices include (a) ensuring that the ventilation systems are operating as intended (i.e., per manufacturer specifications), (b) making changes to the system to increase ventilation, filtration, and outdoor air exchange (i.e., achieving higher standards of air quality), and (c) monitoring indoor carbon dioxide (CO₂) concentrations to ensure that ventilation is working effectively. Enhancing ventilation also improves filtration and energy efficiency, suggested Miller. Persily stated that ventilation systems vary worldwide and that outdoor air may also cause challenges, such as levels of humidity that overload an HVAC system. He stressed the importance of understanding the ventilation system in use, including whether ventilation occurs through infiltration or outdoor air filtration.

Several speakers described monitoring CO₂ levels in parts per million (ppm) as a common method for determining ventilation rate and air exchanges. CO₂ monitoring can be helpful “to verify that you are achieving the ventilation rate that you or someone feels is protective against infection risk,” said Persily, or using CO₂ as a direct or indirect indicator of transmission risk. Speakers suggested that placing the CO₂ sensors near air return grills may provide the best chance for reading signals representative of the overall space. They suggested not placing these sensors in front of supply lines or where people exhale because the readings could be inaccurate. Persily cautions that although CO₂ rates are measured indoors more frequently, and sensors have gotten less expensive in recent years, some of the available technical guidance is unclear, and data are misinterpreted. For example, speakers mentioned that filters remove viral particles but not CO₂ from the air, which may affect transmission risk assessment in spaces that have good air filtration. For accurate interpretation, he suggests accompanying CO₂ concentrations with additional context, for example, building and system design, ventilation timing relative to occupancy rate, sensor location, measurement accuracy, and outdoor concentration. He shared an online calculator that NIST created for measuring CO₂ concentrations.¹⁰

Several speakers also discussed considerations for researchers who work in air quality. They stressed the importance of understanding how CO₂ measures in a research context can be extrapolated to real-world settings, recognizing that all models may not be as effective as real-world tests because of the variability in ventilation systems. Finally, they also noted the importance of speaking with people who design, build, and operate buildings. Some speakers referenced a recent

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National Academies report on Why Indoor Air Chemistry Matters as providing helpful information.¹¹

Noakes stressed the need for good planning, which includes considerations for scaling use of ventilation, filtration, and air cleaning; size and location of the schools; heat loads within and around the school; electrical power and energy involved in systems and available to the school, among other factors. She also highlighted the benefits of working with students to measure CO₂ levels in classrooms and schools. Olsiewski stated that U.S. government funds are now available for schools to implement changes to their ventilation systems. She also suggested bringing in outdoor air as the school’s HVAC system allows, purchasing HEPA filters for every classroom and shared space, using proven ventilation, filtration, and disinfection technologies, and ending enhanced surface and deep cleaning because SARS-CoV-2 is not transmitted via fomites.

Different types and adequate use of filtration or cleaning methods

Several complementary approaches were discussed to remove or disinfect airborne particles. One method that several speakers described was the combined use of filters with in-room, germicidal ultraviolet (UV), which involves lower energy consumption and lower costs than upgrading entire ventilation systems.¹² Olsiewski stated that the HEPA filters remove 99% of fine particles that can pass the walls of the lung and the lung’s blood cells, and the MERV-13 filter removes 50% of the smallest particles, 85% of mid-sized particles, and 90% of the largest particles. The MERV-13 filter, which performs better than the MERV-9 or other filters in experimental and real-world conditions as described by several speakers, along with in-duct UV, demonstrated a 30% reduction even without outdoor air flowing into the system. This percentage increased in buildings where outdoor air was supplied (i.e., effectively diluting the remaining particles in the air indoors). In public vehicles, Conway demonstrated that MERV-13 filters removed particles introduced by a vapor machine more rapidly than MERV-9 filter.

Brent Stephens (Illinois Institute of Technology) categorizes air cleaning systems as either in-duct systems that are integrated within HVAC or systems that are in-room, standalone, or portable and treat air in the room where they are located. These systems can be subtractive by removing particles from the air, or additive, where they add constituents to inactivate or remove particles. Determining which types of technologies to use typically includes referring to information like air flow rate relative to the space size, run time, byproducts, and toxicity. Stephens stated that users need to assess the performance data of various air cleaners to know they are safe to use and meet industry consensus standards. Tests to assess performance include single-pass efficiency test, clean air delivery test, and microbial inactivation tests. Filters with higher ratings in the single-pass efficiency and clean air delivery rate tests also have higher removal of particles, according to Stephens. Air cleaners, when sized appropriately to the room, are highly effective at eliminating contaminations.

Do-it-yourself (DIY) options are available at reduced costs for increased ventilation capacity. Individuals can create cost-effective (~$40-$60/year to maintain) Corsi-Rosenthal DIY air cleaners by attaching minimum efficiency reporting values (MERV) filters to a box fan that performs effectively and costs much less than many commercial options, shared many speakers. Any MERV filter can be used, though MERV-13 or higher is ideal. These DIY air cleaners were initially developed by undergraduate students for use in churches and other facilities during the pandemic, said Quinn.

Ultraviolet light used as a germicidal disinfectant

Some speakers noted that upper-room air ultraviolet germicidal irradiation (UVGI), a UV energy directed above people to eradicate viral, bacterial, and fungal organisms, is a safe and proven technology that effectively removes infectious particles from the air in indoor environments.¹³

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Milton said bars, restaurants, and schools can safely use UVGI, among other controls. Speakers described several experiments wherein UVGI has been demonstrated to reduce the risk of infectious particles in indoor spaces. For decades, UV at a wavelength of 254nm has been used to clean the upper parts of rooms, but to be effective, speakers said that the air needs to be mixed well. Several speakers suggested rooms be designed to allow for airflow and exchange (e.g., the presence of ceiling fans) and reduction of short-range disinfection, possibly via UV treatment.

Newer technologies (e.g., Far-UVC, a short-wavelength UVC within the 200-230nm range¹⁴) have been developed to simultaneously disinfect spaces while not directly exposing people to harmful radiations in those spaces. The advantages of Far-UVC are that it is safe for skin contact, commercially available, and can be used as portable units. Ewan Eadie (Ninewells Hospital, United Kingdom) stated that Far-UVC quickly inactivates airborne and surface pathogens, is equivalent to UVGI, and works in real-world settings, as demonstrated by tests involving tuberculosis transmission. He said that Far-UVC wavelengths do not penetrate and cause reactions in the human skin. Still, there are unknowns about the potential interactions with the human eye and the unintended effects of killing all microbes in the air.

In buses and trains, introducing UV treatment provided inconclusive findings for effectiveness and is less practical to add to existing vehicles than filters, some speakers discussed. Nonetheless, UV treatment can assist in air cleaning for public transport stations and other spaces. Some speakers also stressed that UV treatment might not be effective for transmission that occurs among people who are in very close proximity to each other, so speakers had mixed views on whether Far-UVC could disinfect the air at close ranges.¹⁵ Although Far-UVC is promising, it deserves careful consideration of factors for choosing safe environments for usage while the potential harms are studied further, said Kevin Van Den Wymelenberg (University of Oregon).

VARIABILITY IN ENCLOSED SPACES AND AT-RISK POPULATIONS

Considering the plurality of indoor spaces

Transportation experts highlighted the differences in improving air quality in public transit vehicles and systems as compared to buildings. These differences include both the physical and usage differences between public transit vehicles and buildings. Unlike sedentary buildings, public transit vehicles often experience higher occupancy, transient occupancy, and people in close proximity. One speaker suggested that school buses may present an even greater challenge because of behavioral differences in ridership, specifically stressing the behaviors children tend to display on buses (e.g., speaking loudly, touching each other, and playing around) may increase infectious particles in the air.

Catherine Noakes (University of Leeds, United Kingdom) highlighted unique challenges in United Kingdom educational environments compared to other facilities. Schools have high occupancy levels shared by many people over a long time and are involved in various activities prone to higher risks of viral transmission (e.g., singing and sports). Primary schools are also challenged by managing young children who generally have a lower level of compliance, often poorly maintained and older facilities, and limited capacity to enhance ventilation due to existing outdated infrastructure. External air quality around schools may also present challenges, especially in low-income or highly polluted areas.

Noakes also said that several population factors exist in some places that can help mitigate some of the issues outlined above. For instance, she explained that the risk of infection from SARS-CoV-2 may be lower in U.K. schools than in other facilities because some schools employ layered measures to reduce the chance of infected individuals present in the facilities. These measures include required testing, vaccination, stay-at-home policies, staggered start times, and reduced occupancy. However, closures or absences have significant health and societal impacts; not all parents can keep their

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kids at home. Additionally, many schools may lack the resources and expertise to address the transmission risks of airborne viral particles.

Several speakers noted that spaces like churches or schools come with behavioral considerations, including avoiding indoor spaces that are poorly ventilated for large crowds. This can reduce the chance of a superspreader event, said Li. A study showed that incorporating the concerns, values, and behaviors of enclosed spaces inhabitants into designing engineering controls makes engineered components more effective and perceived as more protective.¹⁶ Crouse-Quinn stated that engineering controls can be part of the solution, especially if they are passive and do not result in huge demands on people. Rev. Anthony Evans, National Black Church Initiative (NCBI), shared how NCBI is piloting a year-long study for members of the Grace Baptist Church in the Bronx, NY, using a layered approach of engineering with behavioral approaches and tailored messaging of medical guidance to reduce viral transmission of SARS-CoV-2. For decades, NCBI has fostered trust and communication between Black church members and health care experts who tailor care towards Black and Latino populations (i.e., culture, traditions, activities, demographics, etc.). In this case, engineering controls to improve air quality focused on updating the church’s HVAC system and increasing outdoor air ventilation. NCBI partners with the Integrated Bioscience and Built Environment Consortium for technical and medical advice and collaborates with the New York State Environmental Protection Agency and New York Department of Health, to measure the effectiveness of exposure controls and to adapt its communications and engagement approaches to address various crises, including the COVID-19 pandemic, monkeypox outbreaks, and other airborne contaminants.

Furthermore, several speakers stated that indoor environments in buildings also vary significantly based on ventilation capacity. For example, Chang-Yu Wu (University of Florida) contrasted the ventilation levels between self-isolation at home, which led to higher viral concentrations because of low ventilation, and gymnasiums, which had lower virus concentrations because of high ventilation. He also contrasted buildings in Southern California, which are newer and equipped with mechanical ventilation and have good natural ventilation, with facilities in the Northeast United States, which do not have good natural ventilation and need to be supplemented with air filtration.

Variability or absence of air quality standards

Speakers explored the importance of regulations, mandated standards, oversight, and enforcement measures to reduce airborne viral particles and improve infection resilience.¹⁷ They stated that standards vary significantly across hazards and regions, including domestically and internationally. Many speakers also shared that standards and codes may often not be written for situations involving potentially high levels of airborne pathogens. In addition, adherence to standards and codes is generally high for newer buildings, but this adherence declines as buildings age.¹⁸ Therefore, some speakers suggested that innovative approaches could be considered to sustain compliance with effective ventilation and filtration standards over time. Some speakers also inquired about how to develop model standards for buildings, which they indicated might promote consistency in the technologies developed and used for ventilation, filtration, and air cleaning while also taking advantage of scientific advances across various fields. Furthermore, some speakers suggested that standards are critical for ensuring that buildings can be designed and built to enhance resilience in indoor environments that may have infectious airborne particles.

Employees and workforce protections

Several speakers shared that in the case of novel infectious agents, workers and employees may not be equipped with all the information they need to

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understand the air quality around them, the risks they can incur, and the ways to mitigate exposure. Facility occupants do not always know their safety relies on ventilation systems. They may use more visible ways to protect themselves, such as cleaning surfaces, which were ineffective for SARS-CoV-2 and even enhanced the perception of risks, as Nick Starkey (Royal Academy of Engineering, United Kingdom) noted. In a longitudinal study at the Boston Hospital, Milton said healthcare workers were being infected despite wearing surgical masks, but Wu shared that providing accurate and timely information allowed healthcare workers to switch from surgical masks to N95, reevaluate workplaces, and enhance disinfection for improved working conditions. Several participants noted that action at the organizational level does not always happen, even with the necessary information. It is often left to individual responsibility, which can lead to workers’ frustration, as shared by Peg Seminario, representing the American Federation of Labor and Congress of Industrial Organizations.

Some speakers repeatedly mentioned the lack of requirements, common standards, and limited oversight in workplaces and schools to guide new building designs or upgrade older facilities for effective ventilation systems. Joe Allen (Harvard University) emphasized that “standards that set the targets for ventilation rate in every space we spend our time are bare minimum standards not been designed with public health experts at that table,” noting that health-based standards with vulnerable populations in mind need to be set in places where people live and work. Many speakers noted that decision makers, such as facility or transportation managers, would likely benefit from access to real-time data about ventilation performance or the presence of infectious agents to assess exposure risks to workers or operators, act appropriately by providing the necessary tools on the ground, and communicate with workers to help “alleviates anxieties” as Wu noted. During pandemics, many employees are not able to work remotely; listening to fears and concerns through virtual town halls is another way to guide workers’ protection, Quinn stated. In many cities, individuals who are most likely to take or work on public transportation often do so out of necessity, resulting in an inequitable system.

Beyond the COVID-19 pandemic, David Rowson, U.S. Environmental Protection Agency, emphasized that “improvements are not only critical component of addressing the source of the virus, but that well-managed indoor air quality has multiple co-benefits” that can result in a range of important health performance, productivity, and economic benefits, including children’s education.

AWARENESS, COMMUNICATION, AND INTEGRATION OF PUBLIC HEALTH WITH POPULATION NEEDS

Trust, transparency, and clear communication as important tools for addressing concerns about risks

Some speakers mentioned how confidence eroded during the COVID-19 pandemic when early guidance was communicated inconsistently. Sandra Crouse Quinn, (University of Maryland, College Park), stated the 2001 anthrax mailings led to a lack of trust between workers and management. She also noted that the unknown risk of SARS-CoV-2 and novel mitigation strategies during the pandemic also degraded the trust of various individuals. Both events, Quinn said, also affected peoples’ perceptions of risk. Helen Jenkins (Boston University) further highlighted the balance between evidence-based decision-making, particularly when scientific studies are being produced rapidly, and maintaining trust. A lack of trust can adversely affect risk perception and compliance with measures like masking. Bi-directional dialogue, engagement, transparency, and proactive communication may help build trust among various actors. Furthermore, multiple speakers discussed the importance of working with members of different groups (e.g., the workforce, teachers, students and parents, and riders) that can help public health officials address issues, overcome barriers, and become familiar with the cultures of different actors who play roles in reducing transmission of airborne pathogens. Jody Holton (SEPTA) reinforced this idea by highlighting trusted community organizations’ role in raising awareness and sharing authoritative resources about various measures such as operator shields on vehicles, mask-wearing, vaccination, and testing.

Wu said strong public health messaging needs to be simple, clear, and accurate. He suggested beginning by defining terms when communicating with others to build a shared understanding of the language and concepts. Similarly, Crouse-Quinn remarked, “every opportunity we’ve had to introduce unfamiliar ways to mitigate risk has become an opportunity for further dialogue and for building trust.” Alternatively, involving people in data collection builds a sense of agency and knowledge to make decisions for themselves and others, said Wu. Furthermore, Katherine Ratliff (U.S. Environmental Protection Agency) discussed how the federal government and industry members could collaborate to standardize technological methods in various settings and extrapolate to real-world applications.

Importance of translating scientific knowledge to decision-making and communication with local communities

Throughout the workshop series, many participants highlighted the importance of messaging and communication for ensuring continued air quality improvement for airborne pathogens and other contaminants. Wu said that information enables behavioral change among people and that access to simple, clear, relevant, and accurate information can equip people with the knowledge they need to make “wise decisions” about improving indoor air quality and protecting themselves. This sentiment extended to decision-making about leveraging the complementary actions of innovation and regulation to enhance air quality. He stressed the importance of using the language and definitions that are understood by audiences from different cultures, disciplines, and other groups. Quinn further stated that ongoing, respectful bi-directional communication is needed, and that people can be part of the solution by implementing measures to reduce infection risks and work toward enhancing health equity by improving air quality. Some speakers suggested that greater knowledge about managing infections can enhance resiliency to these infections at local levels.

Several speakers supported long-term thinking when communicating to key audiences and determining necessary measures. They also said that evidence-supported resources that help to implement measures in low-income regions could address health inequities associated with risks from contaminated indoor spaces. Several speakers raised this suggestion for clear resources and tools to assist decision-makers throughout the workshop series. Some speakers also highlighted examples, including the National Black Church Initiative’s handbook, which contains a step-by-step guide for improving air quality based on verified scientific knowledge. The California Department of Public Health also has guidance based on scientific evidence and provides innovation awards to strengthen the workforce, technology, innovative science and publications, and school monitoring of air quality. While developing these programs, particularly in places with a higher risk of virus transmission, the California Department of Public Health engaged key audiences to build trust, understand needs, and understand the various issues, barriers, and cultures affecting the implementation of various engineering and behavioral measures. Because public health practitioners do not operate in workplaces, engagement with occupational health and safety experts was viewed by several speakers as being a critical part of understanding the particular needs of the relevant workforce.

Other speakers highlighted the importance of foundational research, especially in understanding the spread of viruses between hosts and the environment, and mitigation measures based on the properties of specific viruses in informing decisions about ventilation, filtration, and room cleaning measures. The National Institute of Allergy and Infectious Disease funds the development of technologies for collecting, measuring, and quantifying infectious airborne pathogens. Similarly, the Environmental Protection Agency funds the development of technologies for reducing virus particles in indoor air environments. Several speakers discussed the need for end-to-end research that engages end-users of specific technologies and examines technology adoption. Some participants expressed concern about relying on individual technologies too much and not relying enough on implementing layered approaches for improving indoor air. Furthermore, speakers posed questions about where funds could be

leveraged to improve indoor air quality, such as funds allocated for addressing climate, energy efficiency, and decarbonization.

REFLECTIONS

Many speakers who participated in this workshop series highlighted the critical importance of acknowledging the aerosol transmission of infectious diseases, such as SARS-CoV-2 and other agents, and the effectiveness of combining measures, such as the use of masks, ventilation, filtration, UV, and communication, to yield better outcomes in reducing airborne virus levels. Engineering controls could offer a dependable strategy beyond individual behavior. The significance of higher ventilation rates, especially above 6 ACH, was stressed in any setting while recognizing the various factors influencing virus dispersion and transmission. In addition, variability, uniqueness of school facilities and public transit, and knowledge gaps were considered as challenges that point to the importance of innovative solutions for a safer place to work, learn, and live. The fundamentals of ventilation, filtration, and UV systems in existing buildings were underscored by opportunities for further refinement and integration with behavioral considerations. Some participants also described considerations related to equitable funding, the development of standards in schools and public transportation, and focusing on at-risk populations, including workers who are asked to work in enclosed spaces during pandemics. They also emphasized the importance of effective communication and real-world implementation of interventions to safeguard public health. Building trust may be achieved through dialogues, increased transparency, and early communication with multiple actors. A comprehensive approach to these various strategies, including engineering, social, and health-centered, may result in strengthened integration of public health with society’s everyday needs.

WORKSHOP PLANNING COMMITTEE MEMBERS Linsey C. Marr (co-chair), Virginia Polytechnic; Jonathan M. Samet (co-chair), Colorado School of Public Health; Theresa Chapple-McGruder, Oak Park Department of Public Health; James W. Fox, WSP; John McCarthy, Environmental Health & Engineering, Inc; Catherine Noakes, University of Leeds; Lucas Rocha-Melogno, ICF; Monica Schoch-Spana, Johns Hopkins University Bloomberg School of Public Health; Jeff Vincent, University of California, Berkeley.

DISCLAIMER This Proceedings of a Workshop Series—in Brief was prepared by Kavita Berger, Jessica De Mouy, Audrey Thévenon, and Sabina Vadnais as a factual summary of what occurred at the workshop. The statements made are those of the rapporteur(s) or individual workshop participants and do not necessarily represent the views of all workshop participants; the planning committee; or the National Academies of Sciences, Engineering, and Medicine.

REVIEWERS To ensure that it meets institutional standards for quality and objectivity, this Proceedings of a Workshop Series—in Brief was reviewed by Philomena M. Bluyssen, Delft University of Technology; Linsey C Marr, Virginia Polytechnic; and Katherine Ratliff, U.S. Environmental Protection Agency. Lauren Everett, National Academies of Sciences, Engineering, and Medicine, served as the review coordinator.

SPONSORS These workshops were supported by the Centers for Disease Control and Prevention, the Environmental Protection Agency, and the National Institute of Environmental Health Sciences.

SUGGESTED CITATION National Academies of Sciences, Engineering, and Medicine. 2023. Management of Indoor Air and Airborne Pathogens: Proceedings of a Workshop Series—in Brief. Washington, DC: The National Academies Press: https://doi.org/27316.

Division on Earth and Life Studies Copyright 2023 by the National Academy of Sciences. All rights reserved.