key: cord-278618-7tu5c7m1
authors: Romano-Bertrand, Sara; Aho-Glele, Ludwig-Serge; Grandbastien, Bruno; Gehanno, Jean-François; Lepelletier, Didier
title: Sustainability of SARS-CoV-2 in aerosols: Should we worry about airborne transmission?
date: 2020-06-12
journal: J Hosp Infect
DOI: 10.1016/j.jhin.2020.06.018
sha: 
doc_id: 278618
cord_uid: 7tu5c7m1

nan

SARS-CoV-2 is predominantly transmitted by respiratory droplets and contact with contaminated surfaces but the role of aerosol is debated. The usual personal protective equipment (PPE) recommended for healthcare workers (HCWs) include gown or apron, gloves, protective goggles, head cover and face mask. For the later, the World Health Organization recommends wearing of an anti-projection or surgical mask when caring for COVID-19 patients, and a respirator (filtering facepiece particles (FFP) or N95 mask) only in case of aerosol-generating procedures (AGPs) (https://apps.who.int/iris/bitstream/handle/10665/331498/WHO-2019-nCoV-IPCPPE_use-2020.2eng.pdf). This is based on previous knowledge [1] and the doctrine that: a patient positive for SARS-CoV-2 is contagious by respiratory secretions (>10μm in size) that disseminate only on short distance (<1m); SARS-CoV-2 carried on large droplets settles onto local surfaces and is not stable in the air; SARS-CoV-2 aerosol dispersion is possible during AGPs which extensively expose HCWs and therefore HCWs need to wear a respirator for a higher respiratory protection during AGPs. However, an experimental study of van Doremalen et al, [2] assessed the sustainability of SARS-CoV-2 in aerosols (<5μm at 65% of hygrometry (expressed in %RH for relative humidity)) performed using a high-powered machine that does not reflect normal cough conditions (https://www.who.int/publications-detail/modes-of-transmission-of-virus-causing-covid-19-implicationsfor-ipc-precaution-recommendations). They showed that SARS-CoV-2 remained viable and infective at least 3 hours in aerosols, which opened the debate on SARS-CoV-2 transmission through longdistance aerosols (>1m), and questioned the appropriateness of respiratory protection for HCWs.

An individual who is well, emits 10 to 10 4 particles per liter of expired air, including 95% of <1μm-size particles [3] . When speaking, the rate of emitted particles can reach 5,000 particles per minute, with a size up to 60μm. A cough generates 10 3 to 10 4 particles of size between 0.5 and 30μm (with a predominance of < 2μm particles size) [3] , while a sneeze produces around 10 6 particles between 0.5 and 16μm in size (https://www.anses.fr/fr/system/files/AIR2006et0003Ra.pdf). However, the particles size evolves based on temperature and humidity. Large particle size can rapidly desiccate at high temperature and low humidity, subsequently remaining suspended in the air [4] . Models assessing viral infectivity in aerosols and droplets, focused mainly on influenza virus, showed that respiratory droplets, usually of size between 10 to 100μm at their emission, can rapidly shrink even more when poorly concentrated in organic substances, depending on humidity [5] . Droplets containing mixtures mimicking respiratory mucus decrease from 10μm to 1.9μm under 64 RH%, which significantly extended their time to settle from a height of 1.5m, from 8min to 216min [5] . On the other hand, even if the humidity appears as an important parameter to consider in the potential distance and time of droplets dissemination, it may not modulate the stability of respiratory viruses in aerosols in presence of organic material. A study comparing infectivity of both fine aerosols and stationary droplets containing pandemic influenza A (H1N1) according to seven different conditions of humidity at 25°C

showed no significant differences of infectivity for both aerosols and droplets containing respiratorylike secretions [6] . Furthermore, even if influenza is considered as a droplet-mediated disease, a study showed that 43% of viral RNA emitted from patients was carried on particles of <1μm of diameter, suggesting the potential for airborne transmission [7] .

Under real-life conditions in healthcare settings, a study assessed the extended SARS-CoV-2 dispersion within the hospital environment, by sampling air and surfaces in room of three COVID-19

patients, before routine cleaning for one of them (patient 3) [8] . All environmental samples collected after cleaning in rooms of patients 1 and 2 were negative, while SARS-CoV-2 was retrieved from 61% of surfaces sampled in the room of patient 3. The authors were not able to identify SARS-CoV-2 in air but detected it onto air exhaust outlets, suggesting that the virus in droplets was displaced by airflows and reached the vents [8] . Aerodynamic analysis of SARS-CoV-2 in two hospitals caring for COVID-19

patients in Wuhan showed that SARS-CoV-2 was present in air (including small particles size) especially in confined spaces [9] . But the important limitation of these two studies is that the authors did not demonstrate that SARS-CoV-2 was viable and infectious [8, 9] . Another study of the indoor air in healthcare settings caring for COVID-19 patients in Iran did not detected SARS-CoV-2 in air samples collected 2 to 5 m from the patients' beds with confirmed COVID-19 in ventilated rooms [10] .

However, these results are not transposable to poorly ventilated environments, and airborne transmission may occur in confined spaces in absence of respiratory protection.

The important issues of clinical relevance that remain to be addressed are: what is the infective dose to contaminate a person by inhalation? What is the impact of air ventilation on indoor contamination during the patient hospitalization? The viral load detected by RT-PCR in respiratory specimens can be highly variable between patients [11] and the relationship between viral load in respiratory tract and emitted droplets from patient, along with the viability of SARS-CoV-2 in patient-generated aerosols remain to be demonstrated. Furthermore, the increased infective risk for HCWs seems limited to when AGPs are performed compared to normal ward based care, provided the HCW is wearing a mask [12] .

By considering all these elements, a potential airborne transmission of SARS-CoV-2 cannot be excluded, especially in confined spaces, and needs further investigation. This was already the conclusion of Roy should be considered as droplet preferentially even if airborne transmission under rare specific circumstances has been described [14] .

To date, implementing both droplets and contact precautions for HCWs seems adequate in significantly reducing the risk of infection by SARS-Cov-2 during clinical care, as previously demonstrated for SARS-CoV-1 [1] . To efficiently prevent from contamination, wearing a face mask must be combined with other PPE [1, 15] . The growing anxiety regarding the availability of PPE, especially face masks, urges to rationalize their indications. In order to prevent a supply shortage, the requirement of face mask may be argued on the level of required effectiveness. Respirator (FFP or N95 masks) must be only reserved to HCWs when performing AGPs [15] . A precise list of AGPs should be dressed in order to strictly address the indications of respiratory masks.

Funding: No funding to report.

Conflict of interest: None to declare.

Hospital Hygiene and Infection Control Team

Epidemiology and infection control department. Dijon University Hospital, 14 rue Paul Gaffarel

Service de Médecine Préventive Hospitalière Hygiène, Prévention et Contrôle de l'Infection (HPCI), centre hospitalier universitaire vaudois

Physical interventions to interrupt or reduce the spread of respiratory viruses: systematic review

Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1

Study on transport characteristics of saliva droplets produced by coughing in a calm indoor environment

How far droplets can move in indoor environments--revisiting the Wells evaporation-falling curve

Mechanistic insights into the effect of humidity on airborne influenza virus survival, transmission and incidence

Influenza virus infectivity is retained in aerosols and droplets independent of relative humidity

Measurements of airborne influenza virus in aerosol particles from human coughs

Air, surface environmental, and personal protective equipment contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) from a symptomatic patient

Aerodynamic Analysis of SARS-CoV-2 in Two Wuhan Hospitals

A field indoor air measurement of SARS-CoV-2 in the patient rooms of the largest hospital in Iran

Viral load of SARS-CoV-2

Aerosol generating procedures and infective risk to healthcare workers: SARS-CoV-2 -the limits of the evidence

Airborne Transmission of Communicable Infection -The Elusive Pathway

Viral load distribution in SARS outbreak

Escalating infection control response to the rapidly evolving epidemiology of the Coronavirus disease 2019 (COVID-19) due to SARS-CoV-2 in Hong Kong