Aerosol transmission of SARS-CoV-2? Evidence, prevention and control

Tang, Song; Mao, Yixin; Jones, Rachael M.; Tan, Qiyue; Ji, John S.; Li, Na; Shen, Jin; Lv, Yuebin; Pan, Lijun; Ding, Pan; Wang, Xiaochen; Wang, Youbin; MacIntyre, C. Raina; Shi, Xiaoming

doi:10.1016/j.envint.2020.106039

Cited by 502 publications

(439 citation statements)

References 96 publications

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“…In recent studies, extensive environmental contamination of SARS-CoV-2 in hospital settings has been demonstrated, and viral RNA has been found both in air samples and in samples from air vent openings in isolation rooms [14][15][16][17][18] . Also, the potential for the aerosol transmission route of SARS-CoV-2 is supported by other recent studies 17,[19][20][21] . The increased risk for infection in indoor environments, as well as superspreading events, could be explained by airborne transmission [22][23][24][25][26] .…”

Section: Introductionsupporting

confidence: 69%

Long-distance airborne dispersal of SARS-CoV-2 in COVID-19 wards

Nissen

Krambrich

Akaberi

et al. 2020

Preprint

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Evidence suggests that SARS-CoV-2, as well as other coronaviruses, can be dispersed and potentially transmitted by aerosols directly or via ventilation systems. We therefore investigated ventilation openings in one COVID-19 ward and central ducts that expel indoor air from three COVID-19 wards at Uppsala University Hospital, Sweden, during April and May 2020. Swab samples were taken from individual ceiling ventilation openings and surfaces in central ducts. Samples were subsequently subjected to rRT-PCR targeting the N and E genes of SARS-CoV-2. Central ventilation HEPA filters, located several stories above the wards, were removed and portions analyzed in the same manner. In two subsequent samplings, SARS-CoV-2 N and E genes were detected in seven and four out of 19 room vents, respectively. Central ventilation HEPA exhaust filters from the ward were found positive for both genes in three samples. Corresponding filters from two other, adjacent COVID-19 wards were also found positive. Infective ability of the samples was assessed by inoculation of susceptible cell cultures but could not be determined in these experiments. Detection of SARS-CoV-2 in central ventilation systems, distant from patient areas, indicate that virus can be transported long distances and that droplet transmission alone cannot reasonably explain this, especially considering the relatively low air change rates in these wards. Airborne transmission of SARS-CoV-2 must be taken into consideration for preventive measures.

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Section: Introductionsupporting

confidence: 69%

Long-distance airborne dispersal of SARS-CoV-2 in COVID-19 wards

Nissen

Krambrich

Akaberi

et al. 2020

Preprint

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“…The climatic conditions (eg, temperature and hygrometry) were poorly detailed in studies reviewed, but they may affect the capacity for viral particles to persist in the air. 34 The methods for RNA detection varied, especially the cycle threshold (Ct) for PCR positivity, which also varied from 37 to 45. The RT-PCR Ct values are strongly associated with a cultivable virus.…”

Section: Discussionmentioning

confidence: 99%

Assessment of Air Contamination by SARS-CoV-2 in Hospital Settings

et al. 2020

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IMPORTANCE Controversy remains regarding the transmission routes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).OBJECTIVE To review current evidence on air contamination with SARS-CoV-2 in hospital settings and the factors associated with contamination, including viral load and particle size. EVIDENCE REVIEWThe MEDLINE, Embase, and Web of Science databases were systematically queried for original English-language articles detailing SARS-CoV-2 air contamination in hospital settings between January 1 and October 27, 2020. This study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. The positivity rate of SARS-CoV-2 viral RNA and culture were described and compared according to the setting, clinical context, air ventilation system, and distance from patients. The SARS-CoV-2 RNA concentrations in copies per meter cubed of air were pooled, and their distribution was described by hospital areas. Particle sizes and SARS-CoV-2 RNA concentrations in copies or median tissue culture infectious dose (TCID50) per meter cubed were analyzed after categorization as less than 1 μm, from 1 to 4 μm, and greater than 4 μm. FINDINGS Among 2284 records identified, 24 cross-sectional observational studies were included in the review. Overall, 82 of 471 air samples (17.4%) from close patient environments were positive for SARS-CoV-2 RNA, with a significantly higher positivity rate in intensive care unit settings (intensive care unit, 27 of 107 [25.2%] vs non-intensive care unit, 39 of 364 [10.7%]; P < .001). There was no difference according to the distance from patients (Յ1 m, 3 of 118 [2.5%] vs >1-5 m, 13 of 236 [5.5%]; P = .22). The positivity rate was 5 of 21 air samples (23.8%) in toilets, 20 of 242 (8.3%) in clinical areas, 15 of 122 (12.3%) in staff areas, and 14 of 42 (33.3%) in public areas. A total of 81 viral cultures were performed across 5 studies, and 7 (8.6%) from 2 studies were positive, all from close patient environments. The median (interquartile range) SARS-CoV-2 RNA concentrations varied from 1.0 × 10 3 copies/m 3 (0.4 × 10 3 to 3.1 × 10 3 copies/m 3 ) in clinical areas to 9.7 × 10 3 copies/m 3 (5.1 × 10 3 to 14.3 × 10 3 copies/m 3 ) in the air of toilets or bathrooms. Protective equipment removal and patient rooms had high concentrations per titer of SARS-CoV-2 (varying from 0.9 × 10 3 to 40 × 10 3 copies/m 3 and 3.8 × 10 3 to 7.2 × 10 3 TCID50/m 3 ), with aerosol size distributions that showed peaks in the region of particle size less than 1 μm; staff offices had peaks in the region of particle size greater than 4 μm. CONCLUSIONS AND RELEVANCEIn this systematic review, the air close to and distant from patients with coronavirus disease 2019 was frequently contaminated with SARS-CoV-2 RNA; however, few of these samples contained viable viruses. High viral loads found in toilets and bathrooms, staff areas, and public hallways suggest that these areas should be carefully considered.

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“…The corresponding functional structure however mediates other possible transmission mechanisms which can be due to asymptomatic persons, but in a more extended version where distance no longer matters, for example aerosol transmission. Due to lightweight sneeze micro-particles (those in size), scientists argue that aerosol transmission intensifies indoor virus transmission [ 45 ] and related infection cases from poorly ventilated rooms have been evidenced [ 46 ]. Whether this concept conflicts with the distancing measure emanated from direct transmission will be a factor that needs to be analyzed and treated properly.…”

Section: Resultsmentioning

confidence: 99%

An epidemic model integrating direct and fomite transmission as well as household structure applied to COVID-19

et al. 2021

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This paper stresses its base contribution on a new SIR-type model including direct and fomite transmission as well as the effect of distinct household structures. The model derivation is modulated by several mechanistic processes inherent from typical airborne diseases. The notion of minimum contact radius is included in the direct transmission, facilitating the arguments on physical distancing. As fomite transmission heavily relates to former-trace of sneezes, the vector field of the system naturally contains an integral kernel with time delay indicating the contribution of undetected and non-quarantined asymptomatic cases in accumulating the historical contamination of surfaces. We then increase the complexity by including the different transmission routines within and between households. For airborne diseases, within-household interactions play a significant role in the propagation of the disease rendering countrywide effect. Two steps were taken to include the effect of household structure. The first step subdivides the entire compartments (susceptible, exposed, asymptomatic, symptomatic, recovered, death) into the household level and different infection rates for the direct transmission within and between households were distinguished. Under predefined conditions and assumptions, the governing system on household level can be raised to the community level. The second step then raises the governing system to the country level, where the final state variables estimate the total individuals from all compartments in the country. Two key attributes related to the household structure (number of local households and number of household members) effectively classify countries to be of low or high risk in terms of effective disease propagation. The basic reproductive number is calculated and its biological meaning is invoked properly. The numerical methods for solving the DIDE-system and the parameter estimation problem were mentioned. Our optimal model solutions are in quite good agreement with datasets of COVID-19 active cases and related deaths from Germany and Sri Lanka in early infection, allowing us to hypothesize several unobservable situations in the two countries. Focusing on extending minimum contact radius and reducing the intensity of individual activities, we were able to synthesize the key parameters telling what to practice.

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Aerosol transmission of SARS-CoV-2? Evidence, prevention and control

Abstract: Graphical abstract

Cited by 502 publications

References 96 publications

Long-distance airborne dispersal of SARS-CoV-2 in COVID-19 wards

Long-distance airborne dispersal of SARS-CoV-2 in COVID-19 wards

Assessment of Air Contamination by SARS-CoV-2 in Hospital Settings

An epidemic model integrating direct and fomite transmission as well as household structure applied to COVID-19

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