An upper bound on one-to-one exposure to infectious human respiratory particles

Abstract

There is ample evidence that masking and social distancing are effective in reducing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission. However, due to the complexity of airborne disease transmission, it is difficult to quantify their effectiveness, especially in the case of one-to-one exposure. Here, we introduce the concept of an upper bound for one-to-one exposure to infectious human respiratory particles and apply it to SARS-CoV-2. To calculate exposure and infection risk, we use a comprehensive database on respiratory particle size distribution; exhalation flow physics; leakage from face masks of various types and fits measured on human subjects; consideration of ambient particle shrinkage due to evaporation; and rehydration, inhalability, and deposition in the susceptible airways. We find, for a typical SARS-CoV-2 viral load and infectious dose, that social distancing alone, even at 3.0 m between two speaking individuals, leads to an upper bound of 90% for risk of infection after a few minutes. If only the susceptible wears a face mask with infectious speaking at a distance of 1.5 m, the upper bound drops very significantly; that is, with a surgical mask, the upper bound reaches 90% after 30 min, and, with an FFP2 mask, it remains at about 20% even after 1 h. When both wear a surgical mask, while the infectious is speaking, the very conservative upper bound remains below 30% after 1 h, but, when both wear a well-fitting FFP2 mask, it is 0.4%. We conclude that wearing appropriate masks in the community provides excellent protection for others and oneself, and makes social distancing less important.

Modelling the direct virus exposure risk associated with respiratory events

“…The second aspect is accounted for by following the study by Cheng et al [53], in which the size-dependent particle penetration rate of surgical and N95 masks based on the past literature [56,57] is calculated. Additional findings on face mask efficiency can be found in the experimental study of Bagheri et al [54] and in the theoretical one of Mao & Hosoi [58], with the latter mainly focused on airborne aerosols with size smaller than 1 μm. As it is known that the breathing airflow could escape from the edge area owing to improper mask fit [21,51], for each type of mask, we also consider a case in which leakages of respiratory droplets occur.…”

“…More recently, wearing face masks has been widely accepted as a well-established protective measurement, providing both 'inward' protection by filtering virus-laden aerosolized particles that would be inhaled by an uninfected person and 'outward' protection by trapping virus-laden droplets expelled by an infected person [1]. Recent studies [21,[50][51][52][53][54] have provided evidence that supports the ability of face masks in reducing pathogen transmission. We focus here on the 'outward' protection provided by two standard face coverings, i.e.…”

“…This observation can be traced back to the ability of masks in blocking large droplets, which load more virus copies than smaller droplets (assuming a uniform viral load across all droplets diameters). Indeed, experimental data recently published showed that masks are highly effective in blocking respiratory droplets larger than about 20 μm [53,54]. In addition, the suppressing effect of masks on airflow velocity results in a shorter The characteristic velocity of the respiratory events considered is assumed equal to 1 m s −1 (speaking), 10 m s −1 (coughing) and 30 m s −1 (sneezing).…”

Aerosol decontamination and spatial separation using a free-space LED-based UV-C light curtain

“…The most effective way of protection are respiratory masks with a very tight fit without any leaks. If using the proper filtration materials, almost complete protection can be achieved [22,23] . Thereby, the materials filter larger particles with higher efficiency than smaller particles around 0.3 µm [24] .…”

Préconisations pour protéger les patients de la filière oncologique face au variant Omicron

“…Proposition 5 : port d’un masque de protection de type Filtering Face Piece type 2 (FFP2/N95) pour les patients en cours de traitement actif, dont certains (avec cancer pulmonaire, hémopathie lymphoïde…) ont un risque de décès de 30 % ou plus en cas de contamination, dans les lieux avec du public. De récentes données comparatives en conditions expérimentales évaluent une protection individuelle supérieure par rapport au port de masques chirurgicaux [ 19 ]. Le gain peut apparaître cependant limité si le port des masques chirurgicaux était bien respecté par tous, mais cette condition apparaît peu réaliste dans les lieux avec public (cinéma, transports en commun etc.)…”