Indoor Air Changes and Potential Implications for SARS-CoV-2 Transmission

Abstract

Buildings have been associated with spread of infectious diseases, such as outbreaks of measles, influenza, and Legionella. With SARS-CoV-2, the majority of outbreaks involving 3 or more people have been linked with time spent indoors, and evidence confirms that far-field airborne transmission (defined as within-room but beyond 6 feet) of SARS-CoV-2 is occurring. 1 Controlling concentrations of indoor respiratory aerosols to reduce airborne transmission of infectious agents is critical and can be achieved through source control (masking, physical distancing) and engineering controls (ventilation and filtration). 2 With respect to engineering controls, an important flaw exists in how most buildings operate in that the current standards for ventilation and filtration for indoor spaces, except for hospitals, are set for bare minimums and not designed for infection control. Several organizations and groups have called for increasing outdoor air ventilation rates, but, to date, there has been limited guidance on specific ventilation and filtration targets. This article describes the rationale for limiting far-field airborne transmission of SARS-CoV-2 through increasing outdoor air ventilation and enhancing filtration, and provides suggested targets.To reduce far-field airborne transmission of SARS-CoV-2 in smallvolume indoor spaces (eg, classrooms, retail shops, homes if guests are visiting), the suggestions include targeting 4 to 6 air changes per hour, through any combination of the following: outdoor air ventilation; recirculated air that passes through a filter with at least a minimum efficiency rating value 13 (MERV 13) rating; or passage of air through portable air cleaners with HEPA (high-efficiency particulate air) filters.Despite the dose-response for SARS-CoV-2 being unknown, and continued scientific debate about the dominant mode of transmission, evidence support these suggestions. First, SARS-CoV-2 is primarily transmitted from the exhaled respiratory aerosols of infected individuals. Larger droplets (>100 μm) can settle out of the air due to gravitational forces within 6 feet, but people emit 100 times more smaller aerosols (<5 μm) during talking, breathing, and coughing. Smaller aerosols can stay aloft for 30 minutes to hours and travel well beyond 6 feet. 1 Second, high-profile and welldescribed SARS-CoV-2 outbreaks across multiple space types (eg, restaurants, gyms, choir practice, schools, buses) share the common features of time indoors and low levels of ventilation, even when people remained physically distanced. 3 Third, these suggestions are grounded in the basics of exposure science and inhalation dose risk reduction. Higher ventilation and filtration rates more rapidly remove particles from indoor air, thereby reducing the intensity of exposure and duration that respiratory aerosols stay aloft inside a room. Fourth, this approach is consistent with what is used in hospitals to minimize risk of transmission (eTable in the Supplement). Fifth, reviews on the relationship between ventilation and inf...

COVID-19, the Built Environment, and Health

“…Health Officer this facility is limited to 50% occupancy load through April 5, 2020. some have suggested that new HVAC paradigms are needed. These will need to balance thermal comfort, fresh air exchanges, and reducing energy use (Allen and Ibrahim 2021;Burridge et al 2021;Ferdyn-Grygierek et al 2019). Two examples of such an approach are supplying personal ventilation directly to people's individual breathing zones (say, at their workstations; Figure 3B) instead of ventilating the entire interior building space (Figure 3A) (Melikov 2020) and using precision HVAC based on localized monitoring and artificial intelligence guidance (Ding et al 2020).…”

Nosocomial Outbreak of COVID-19 in a Hematologic Ward

“…Recent studies have detected viable SARS-CoV-2 in air samples from rooms occupied by COVID-19 patients where there were no aerosol generating events, and from the car of an infected person [ 11 12 ]. In addition, data has now suggested aerosol transmission of SARS-CoV-2 as a major mode of transmission [ 1 2 3 4 ]. We performed an airflow simulation and demonstrated that air was spread from the poorly ventilated bathroom to the adjacent Room 1, where Case 7 stayed.…”

“…SARS-CoV-2 infection in hospitalized patients with underlying disease is associated with a poor prognosis, and rapid SARS-CoV-2 transmission makes containment of the outbreak challenging. In addition, there is growing evidence for airborne-transmission of SARS-CoV-2 [ 1 2 3 4 ] and previous studies suggest that thorough investigation should be performed including the possibility of airborne-transmission [ 5 6 7 ].…”

Orthodoxy, illusio, and playing the scientific game: a Bourdieusian analysis of infection control science in the COVID-19 pandemic

“…Whilst the message from aerosol scientists that transmission of SARS-CoV-2 is predominantly airborne was ignored and dismissed within the medical and health policy mainstream during 2020, the heterodoxy did not die. On the contrary, by spring 2021 the dominance of airborne transmission was becoming more accepted even within medical circles -for example, in January 2021 the Journal of Hospital Infection published a paper entitled 'Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)' 87 , and in April 2021, the British Medical Journal commissioned an editorial from an overlapping team entitled 'Covid-19 has redefined airborne transmission' 14 , the Lancet published 'Ten scientific reasons in support of airborne transmission of SARS-CoV-2' 2 and the Journal of the American Medical Association published a review article on ventilation and filtration 88 . Whilst the WHO remained resistant to the phrase 'airborne transmission', it placed increasing emphasis on ventilation in late 2020 and into 2021 (source A17, Table 1 25 ).…”