Intermittent occupancy combined with ventilation: An efficient strategy for the reduction of airborne transmission indoors

Abstract

It is important that efficient measures to reduce the airborne transmission of respiratory infectious diseases (including COVID-19) should be formulated as soon as possible to ensure a safe easing of lockdown. Ventilation has been widely recognized as an efficient engineering control measure for airborne transmission. Room ventilation with an increased supply of clean outdoor air could dilute the expiratory airborne aerosols to a lower concentration level. However, sufficient increase is beyond the capacity of most of the existing mechanical ventilation systems that were designed to be energy efficient under non-pandemic conditions. We propose an improved control strategy based on source control, which would be achieved by implementing intermittent breaks in room occupancy, specifically that all occupants should leave the room periodically and the room occupancy time should be reduced as much as possible. Under the assumption of good mixing of clean outdoor supply air with room air, the evolution of the concentration in the room of aerosols exhaled by infected person(s) is predicted. The risk of airborne cross-infection is then evaluated by calculating the time-averaged intake fraction. The effectiveness of the strategy is demonstrated for a case study of a typical classroom. This strategy, together with other control measures such as continuous supply of maximum clean air, distancing, face-to-back layout of workstations and reducing activities that increase aerosol generation (e.g., loudly talking and singing), is applicable in classrooms, offices, meeting rooms, conference rooms, etc.

Influenza and Influenza Vaccine: A Review

“…If a susceptible person touches a contaminated surface such as a phone, countertop, keyboard, door handle, or another individual's contaminated hand and then places their hand on or near their nose, mouth, or eyes, the virus can be transmitted 13 . Viral transmission has also been implicated via the airborne route (particles ≤5 microns that remains suspended in air) through aerosolization of droplets that can occur with singing, shouting, and specific medical procedures 18,19 . Influenza viruses can remain infectious on surfaces other than the body for extended periods of time, often days to weeks 20 …”

“…Once the diagnosis of influenza is made, the clinician should counsel the individual about personal protective measures to prevent further spread of the illness in the home and community. Examples of effective personal protective measures are respiratory etiquette (covering mouth with elbow or tissue during coughing and sneezing), use of disposable tissues, proper hand hygiene (eg, soap and water and/or alcohol‐based gel), and use of facemasks (eg, surgical or N95 respirators) 19,23 . Instructions that alcohol, chlorine, hydrogen peroxide, soaps/detergents, and iodine‐based antiseptics kill influenza viruses that are on surfaces should be provided 24 .…”

“…Social distancing, self‐quarantine, and other strategies to reduce airborne transmission of influenza must also be discussed. Improving room ventilation by opening a window and replacing the inside air with clean outdoor air may dilute the sick person's expiratory airborne aerosols to a lower concentration level, decreasing risk of transmission 19 . Air purifiers dilute particles in the air without actually filtering out the virus and therefore are not appropriate for use as a personal protective measure 25 .…”

Multifaceted highly targeted sequential multidrug treatment of early ambulatory high-risk SARS-CoV-2 infection (COVID-19)

“…Since exhaled air in an infected person is considered to be "loaded'' with particulate inoculum, each exhalation and inhalation in theory reinoculates the nasophar-ynx and tracheobronchial tree (Chen, 2020). We propose that fresh circulating air could reduce reinoculation and potentially lessen the severity of illness and possibly limit household spread during quarantine (Melikov et al, 2020). This calls for open windows, fans for aeration, or spending long periods of time outdoors away from others with no face covering in order to disperse and not reinhale the viral bioaerosol.…”

Modelling uncertainty in the relative risk of exposure to the SARS-CoV-2 virus by airborne aerosol transmission in well mixed indoor air

“…1 Infection risk is often estimated using the established Wells–Riley model that gives the required quanta emission (emission of infective material) from known outbreaks [8] , fitting to the reproductive number, [33] , or is calculated from first principles [34] . Mass balance models have also been used to investigate transient effects and the role purging room air during breaks [35] . The impact of varying occupancy has also been considered using the re-breathed fraction of air based on respiratory CO generation and removal [36] .…”