Airborne transmission of SARS-CoV-2 in indoor environments: A comprehensive review

Figures & data

Fig. 1. Timeline of major studies on the airborne transmission of COVID-19 and responses from public agencies (data as of April 19th, 2021 (WHO 2021a)) (Google Trends index indicates the worldwide query data on “COVID airborne” on Google (2020). The index is calculated to be ranged from 0 to 100 (Choi and Varian 2012)).

Table 1. Major studies on the airborne transmission of SARS-CoV-2.

Reference^a	Settings	Findings
Onsite virus measurements in the air or aerosols
Binder et al. (2020)	Hospital rooms	Very few aerosol samples detected positive (3/195)^b; None of the aerosol samples showed evidence of viable virus;
Cheng et al. (2020b)	Hospital rooms	Air samples detected negative (0/8)
Cheng et al. (2020a)	Hospital rooms	Air samples detected negative (0/6 patients)
Chia et al. (2020a)	Hospital rooms	Air samples detected positive (2/3 rooms)^c (1.84 × 10^3 − 3.38 × 10^3 RNA copies/m^3)^d
de Man et al. (2020)	Nursing home with infectors	Viral RNA detected in the HVAC system of a nursing home
Ding et al. (2021)	Hospital rooms	Air samples detected positive (1/46)
Döhla et al. (2020)	Quarantined households (flats or houses) with at least one infector	Air samples detected negative (0/15)
Dunker et al. (2021)	Hospital rooms	Air samples detected negative
Faridi et al. (2020)	Hospital rooms	Air samples detected negative (0/10)
B. Feng et al. (2021)	Hospital rooms	Air samples detected positive (1/12) (1112 copies/m^3 in <1 µm aerosols, 745 copies/m^3 in >4 µm aerosols)
Z. D. Guo et al. (2020)	Hospital rooms	Air samples detected positive (14/40)
Hadei et al. (2021)	Public places and transportation	Air samples detected positive (18/28)
Horve et al. (2020)	Hospital HVAC systems	Viral RNA detected at the supply air damper (5/15)
Jiang et al. (2020)	Hospital rooms	Air samples detected positive (1/28)
Jin et al. (2021)	Hospital rooms	Air samples detected positive (1/1)
Kenarkoohi et al. (2020)	Hospital rooms	Air samples detected positive (2/14)
J. Y. Kim et al. (2020)	Hospital rooms	Air samples detected negative (0/52)
Lane et al. (2020)	Hospital rooms	Air samples detected negative in the rooms of patients on ventilators (0/30)
Lednicky et al. (2020)	Hospital rooms	Viable (infectious) virus detected in aerosols (4/6) (6–74 viruses/L)
Lednicky et al. (2021)	Car	Viable (infectious) virus detected in airborne particles of the size range of 0.25 to 0.5 µm in a car driven by a COVID-19 patient
Y. Li et al. (2020)	Hospital rooms	Aerosol samples detected negative (0/135)
Liu et al. (2020)	Hospital rooms	Air samples detected positive (21/35) (1–42 RNA copies/m^3); Resuspension of deposited particles is a potential transmission pathway;
Ma et al. (2020)	Hospital rooms or quarantined hotel	Air samples detected positive in an unventilated hotel toilet (1/26)
Maestre et al. (2021)	Quarantined household with infected occupants	Viral RNA detected on the filter of the HVAC system (approximately 69 ± 43 RNA copies/m^3); The detected viral RNA does not imply infectivity;
Masoumbeigi et al. (2020)	Hospital rooms	Air samples detected negative (0/31)
Moore et al. (2021)	Hospital rooms	Air samples detected positive (4/55) (<10–460 RNA copies/m^3); Viable (infectious) virus was not recovered from any positive air sample;
Moreno et al. (2021)	Public transportations	Air samples detected positive (3/12); The potential infectivity of the positive samples is considered to be extremely low;
Mouchtouri et al. (2020)	Hospital rooms, nursing home, ferry boat, long-term care facility	Air samples detected positive (1/12); Viral RNA detected on air exhaust duct surface and the filter of the HVAC system;
Nakamura et al. (2020)	Hospital rooms	Air samples detected negative (0/11)
Nissen et al. (2020)	Hospital rooms	Virus detected in ventilation systems
Ong et al. (2020)	Hospital rooms	Air samples detected negative (0/3 rooms); Surface samples on air exhaust outlets detected positive;
Razzini et al. (2020)	Hospital rooms	Air samples detected positive (100% in contaminated areas)
Santarpia et al. (2020)	Hospital rooms	Air samples detected positive (11/18 rooms/patients) (2.42–8.34 RNA copies/L for air samples in patient rooms, 2.08–8.69 RNA copies/L for hallway air samples, 5.37–48.22 RNA copies/L for personal air samples); Viable (infectious) virus detected in some samples;
Setti et al. (2020a)	Outdoor environments	Air samples detected positive (20/34)
Stern et al. (2021)	Hospital rooms	Air samples detected positive (9%)
Tan et al. (2020)	Hospital rooms	Air samples detected positive during an intubation procedure (1/12)
Zhou et al. (2021)	Hospital rooms	Air samples detected positive (3/44) (9–219 viruses/m^3); Virus observed in exhaled breath (2/9) (∼10^5 RNA copies/m^3)
Laboratory experiments
Dabisch et al. (2020)	Experimental conditions	The time needed for a 90% decrease in infectious virus ranged from 4.8 min under simulated high-intensity sunlight, to greater than 2 h without sunlight
Fears et al. (2020)	Experimental conditions	Infectivity and virion integrity maintained for up to 16 h in aerosols
Schuit et al. (2020)	Experimental conditions	Mean decay rates of aerosols under simulated sunlight were 0.121–0.306 min^−1 (90% loss, 8–19 min) and mean decay rate without simulated sunlight was 0.008 min^−1 (90% loss, 286 min)
Smither et al. (2020)	Experimental conditions	Half-lives of infectious virus ranged from 30 to 177 min for the different conditions
van Doremalen et al. (2020)	Experimental conditions	Half-lives of infectious virus in aerosols were around 1.1 h
Retrospective analysis on real outbreak events
Almilaji and Thomas (2020)	Cruise ship	Airborne transmission of COVID-19 through the ventilation system on the Diamond Princess cruise ship could explain the higher-than-expected virus spread into cabins without previously confirmed cases during the quarantine period
Azimi et al. (2021)	Cruise ship	Aerosol inhalation was likely the dominant contributor to viral transmission on the Diamond Princess cruise ship
Buonanno, Morawska, and Stabile (2020)	Restaurant and choir in a church	Airborne transmission was likely the main route for spreading the virus during the outbreaks in a restaurant in Guangzhou and a choir in Mount Vernon
J. Cai et al. (2020)	Shopping mall	Transmission through aerosols in the confined space was likely associated with a cluster of COVID-19 cases in a shopping mall in Wenzhou
Chau et al. (2021)	Bar	The superspreading event at a bar in Ho Chi Minh City indicated that crowds in enclosed indoor settings with poor ventilation may be considered at high risk for transmission
Crema (2021)	Regions around the Amazon rainforest	Airborne transmission was likely the key to explain the remarkable viral spreading around the Amazon rainforest
Eichler et al. (2021)	Quarantined hotel	Aerosols were the probable mode of transmission in a quarantined hotel in New Zealand, and the enclosed and unventilated space in the hotel corridor probably facilitated the spread
Günther et al. (2020)	Meat processing plant	Transmission of SARS-CoV-2 can occur over distances of at least 8 m in confined spaces in a German meat processing plant under conditions without sufficient ventilation
Hwang et al. (2021)	Apartment building	Airborne transmission through the air duct in the restroom was likely the primary reason to explain the virus spreading among the infectors in an apartment building in Seoul
Kang et al. (2020)	Apartment building	Vertical spread of virus-laden fecal aerosols via stacks and vents was likely the reason for the outbreak in a high-rise flat building in Guangzhou, supported by the positive environmental samples
Katelaris et al. (2021)	Choir in a church	Airborne transmission was suggested since the case patients seated up to 15 m from the index patient without close physical contact during church singing in Sydney
Khanh et al. (2020)	Aircraft	Transmission through aerosols was likely occurred in the business class area during a long-haul flight to Vietnam, where seats are already more widely spaced than in economy class, and infection spread much further than the existing 2-row or 2-meter rule recommended for COVID-19 prevention on airplanes and other public transport would have captured
Y. Li et al. (2020)	Restaurant	Aerosol transmission due to poor ventilation may explain the viral spreading in a restaurant in Guangzhou
Luo et al. (2020)	Tour coach and minibus	Airborne transmission may explain the high attack rate on a tour coach and a minibus in Hunan province
Miller et al. (2020)	Choir in a church	Transmission by the aerosol route was likely; it appeared unlikely that either fomite or ballistic droplet transmission could explain a substantial fraction of the cases in a choir in Mount Vernon
Y. Shen et al. (2020)	Tour coach	Airborne spread of the virus may at least partially explain the markedly high attack rate observed on a tour coach in Zhejiang province
S. Tang et al. (2020)	Onsite tracer simulation experiment in an apartment	Aerosols were observed in the restrooms on 25th and 27th floors after flushing the toilet in the 15-floor restroom, which possibly explained the virus spreading between the studied rooms in an apartment building in Guangzhou
Wang and Du (2020)	Apartment building	Airborne transmission was likely the primary reason to explain the virus spreading in an apartment building in Ordos
R. Zhang et al. (2020)	Outbreaks in China, Italy, and NYC	Airborne transmission was highly virulent and represented the dominant route to spread the disease
Animal experiments
Y. I. Kim et al. (2020)	Experiments on ferrets	Airborne spread observed
Kutter et al. (2021)	Experiments on ferrets	SARS-CoV-2 is transmitted through the air
Richard et al. (2020)	Experiments on ferrets	SARS-CoV-2 is transmitted efficiently via the air
Shi et al. (2020)	Experiments on domesticated animals	Viruses were transmissible between cats via the airborne route

^a Listed in alphabetical order.

^b Proportion of positive samples in all available samples (i.e. positive samples/all samples).

^c Air samples in two out of three rooms detected positive. Totally 18 samples were collected (six for each room), but the positive sample number was not reported.

^d Measured viral concentration.

Table 2. Number concentration and proportion in different sizes of expelled particles during different activities (adapted from Morawska et al. (2009)).

Particle diameter [µm]	Number concentration [cm^−3] and proportion [%] in different sizes of expelled particles
	Voiced counting	Whispered counting	Unmodulated vocalization	Unmodulated whisper	Breathing	Coughing
≤0.80 ± 0.08	0.236 (73.3%)	0.110 (84.6%)	0.751 (69.0%)	0.636 (94.6%)	0.084 (85.7%)	0.567 (83.6%)
1.8 ± 0.3	0.068 (21.1%)	0.014 (10.8%)	0.139 (12.8%)	0.037 (5.5%)	0.009 (9.2%)	0.093 (13.7%)
3.5 ± 0.7	0.007 (2.2%)	0.004 (3.1%)	0.139 (12.8%)	0.000 (0%)	0.003 (3.1%)	0.012 (1.8%)
5.5 ± 1.0	0.011 (3.4%)	0.002 (1.5%)	0.059 (5.4%)	0.000 (0%)	0.002 (2.0%)	0.006 (0.9%)
Total	0.322	0.130	1.088	0.672	0.098	0.678

Table 3. Concentration and distribution of airborne SARS-CoV-2 across particle diameters.

Scenarios	SARS-CoV-2 concentration [RNA copies/m^3]		Reference
	Size distribution	Total
Protective-apparel removal room	0–0.25 µm: 0 0.25–0.5 µm: 40 0.5–1 µm: 0 1–2.5 µm: 1 >2.5 µm: 1	42	Liu et al. (2020)
Protective-apparel removal room	0–0.25 µm: 1 0.25–0.5 µm: 2 0.5–1 µm: 9 1–2.5 µm: 1 >2.5 µm: 7	20
Medical staff’s office	0–0.25 µm: 3 0.25–0.5 µm: 2 0.5–1 µm: 2 1–2.5 µm: 3 >2.5 µm: 10	20
Patient room with a symptomatic infector (sampled near the exhaust, >1 m from the patient)	<1 µm: 0 1–4 µm: 0 >4 µm: 0	0	Chia et al. (2020b)
Patient room with a symptomatic infector (sampled within 1 m from the patient)	<1 µm: 0 1–4 µm: 1384 >4 µm: 2000	3384
Patient room with an asymptomatic infector (sampled within 1 m from the patient)	<1 µm: 0 1–4 µm: 916 >4 µm: 927	1843
Patient room with a symptomatic infector (sampled at the bedside, 0.2 m from the bed)	<1 µm: 1112 1–4 µm: 0 >4 µm: 745	1857	Z. Feng et al. (2021)
Hospital corridor	/	9	Zhou et al. (2021)
Hospital ICU room with infector(s)	/	21
Patient room with infector(s) (sampled at bedside)	/	219
Two four-bed cohort bays with symptomatic infectors (sampled <1 m from four different patients)	/	<10–460	Moore et al. (2021)
Patient rooms with symptomatic infector(s) (sampled >1 m from the patient)	/	2.70–8.34 × 10^3	Santarpia et al. (2020)
Patient rooms with symptomatic infector(s) (sampled >2 m from the patient)	/	2.42–2.48 × 10^3
Patient room with symptomatic infector(s) (sampled near the patient)	/	4.07 × 10^3
Hospital hallways	/	2.08–8.69 × 10^3
Personal air samples	/	5.37–48.22 × 10^3
Unventilated quarantine hotel toilet room	/	6.07 × 10^3	Ma et al. (2020)
Patient room with two infectors (sampled 2 m from patient 1 and 4.6 m from patient 2)	/	74 × 10^3	Lednicky et al. (2020)
Patient room with one infector (sampled 2 m from the patient)	/	18 × 10^3
Patient room with two infectors (sampled 4.8 m from patient 1 and 3 m from patient 2)	/	27 × 10^3
Patient room with one infector (sampled 4.8 m from the patient)	/	6 × 10^3

Fig. 2. COVID-19 outbreaks in various settings in Colorado (data as of May 26th, 2021 (CDPHE 2020)) and Michigan (data as of May 20th, 2021 (MDHHS 2020)).

Fig. 3. Relationship between occupant density and designed total ventilation rate per person in different scenarios based on ASHRAE 62.1 (data adapted from J. Shen et al. (2021)).

Table 4. Quanta emission rates (ER) of SARS-CoV-2 particles in different studies.

Activity	ER [h^−1]	Introduction	Reference
Estimated from retrospective analysis on real outbreak events
Standing + singing	970 ± 390	Skagit Valley Chorale superspreading event	Miller et al. (2020)
Standing + singing	341	Skagit Valley Chorale superspreading event	Buonanno, Morawska, and Stabile (2020)
Standing + singing	870	Skagit Valley Chorale superspreading event	Bazant et al. (2021)
Seated + vocalization	61	Guangzhou restaurant outbreak event	Buonanno, Stabile, and Morawska (2020)
Resting + breathing	45	Zhejiang tour coach outbreak event	Bazant et al. (2021)
Resting + breathing	30	Diamond Princess cruise ship outbreak event	Bazant et al. (2021)
Resting + breathing	29	Wuhan city outbreaks	Bazant et al. (2021)
Resting + breathing	185.63	Diamond Princess cruise ship outbreak event	Chen et al. (2021)
Estimated using the viral load model
Resting	<1		Buonanno, Stabile, and Morawska (2020)
Intermediate	≤100	Estimated based on the viral load in the sputum
Light activity + vocalization	>100
Resting + breathing/whispering^a	3	Estimated based on cv = 10^9 RNA copies/mL and ci = 0.02	Buonanno, Morawska, and Stabile (2020)
Standing + breathing/whispering	3
Light activity + breathing/whispering	9
Resting + speaking^b	50
Standing + speaking	56
Light activity + speaking	142^c
Estimated using statistical methods
Sedentary state	14–48	Estimated based on the fitting curve between ER and R0 from the data of other respiratory diseases (e.g. influenza and SARS-CoV-1)	Dai and Zhao (2020b)

^a Breathing/whispering represents the mean value between whispering and breathing (Buonanno, Stabile, and Morawska 2020).

^b Speaking is considered as the mean value between unmodulated vocalization and voiced counting (Buonanno, Stabile, and Morawska 2020).

^c This value was adopted by many studies (Harrichandra, Ierardi, and Pavilonis 2020; S. Zhang and Lin 2020).

Table 5. IAQ control strategies for mitigating the risk of airborne transmission.

Category	Strategy	Effectiveness	Effective scale	Capital cost^a	Durability	Accessibility
PPE	Cloth mask	30% particle filtration efficiency for purchased masks (considering leakage from gaps caused by improper fit) (Konda et al. 2020); 20% particle filtration efficiency for homemade masks (cotton and nylon materials) (M. Zhao et al. 2020)	Breathing zone	US$3/count (purchased); US$0/count (homemade)	Reusable	Easy^b; Homemade (using household materials like cotton and nylon (A. Davies et al. 2013)); Comfort should be considered
	Surgical mask	50% particle filtration efficiency (considering leakage from gaps caused by improper fit) (Konda et al. 2020; Rothamer et al. 2020)	Breathing zone	US$0.2/count	Disposable^c	Depending on supply capacity (including conventional, contingency, and crisis situations (U.S. CDC 2021d)); Comfort should be considered
	N95 mask	95% particle filtration efficiency (without gaps)^d (Konda et al. 2020)	Breathing zone	US$2/count	Disposable^c	Depending on supply capacity (including conventional, contingency, and crisis situations (U.S. CDC 2021d)); Comfort should be considered;
	Face shield	23% reduction on aerosol inhalation under long-time use (more aerosol reduction under short-distance use) (Lindsley et al. 2014)	Breathing zone	US$2/count	Reusable	Easy; Homemade (using plastic sheets and other materials);
	Mask fitter/sealer/brace^e	Greatly improving the efficiency of masks by reducing the leakage through gaps (e.g. improve the particle filtration efficiency of surgical masks to over 90% (Rothamer et al. 2020))	Breathing zone	US$9/count (purchased (UW Madison 2020)); US$0/count (homemade)	Reusable	Easy; Homemade (using rubber or other materials (Fix The Mask 2020)); Increased discomfort
Ventilation	Upgrading filters of building ventilation systems (e.g. HEPA)	99.9% removal efficiency for particles >0.3 µm (HEPA filter)	Building	US$280/count (with an increase in fan power due to the increased pressure rise through higher-rating filters (Risbeck et al. 2021))	Replaced every 6–12 months	Easy
	Increasing outdoor air supply of building ventilation systems (e.g. 100% outdoor air)	Largely increasing the ventilation rate of the room (e.g. providing 60% more clean air compared to a reference system with 25% outdoor air and MERV 8 filter)	Building	US$5/m^2·year for extra energy consumption (central system); US$10/m^2·year for extra energy consumption (individual unit)^g (U.S. EIA 2018)	Long-term use^f	Easy (switching the damper to increase outdoor air supply)
	Personal ventilation (for fresh air supply)	Increasing clean air supply to the personal microenvironment with typical ventilation effectiveness of 1.7, depending on diffuser location and airflow rate (A. Melikov, Grønbaek, and Nielsen 2007)	Personal environment	Varying greatly (depending on system scale)	Long-term use (filters need regular replacements)	Need professional design and installation
	Local air exhaust	Reducing the cross-contamination with typical ventilation effectiveness of 1.4 to 10, depending on the local partition configuration, exhaust location, and airflow rate (Dygert and Dang 2012)	Personal environment	Varying greatly (depending on system scale)	Long-term use	Need professional design and installation
	Displacement ventilation	Improving the clean air delivery efficiency with typical ventilation effectiveness of 1.2 to 2 (Q. Chen and Glicksman 2003)	Room	Varying greatly (depending on system scale)	Long-term use (filters need regular replacements)	Need professional design and installation
	Natural ventilation	Providing more outdoor air to the room, e.g. >10 h^−1 air changes in some scenarios (Qian et al. 2010) (depending on window opening conditions, wind condition, and building geometry)^h	Room	US$0	Long-term use	Depending on weather and outdoor air quality conditions
	Closing doors between rooms (separating rooms and blocking airflow across rooms)	Reducing cross contamination across rooms (cross-contamination risk can be eliminated when the doors are fully closed)	Building/room	US$0	Long-term use	Easy (need to coordinate with occupant schedules)
Partition	Partition screens	Depending on airflow patterns in the room (well-designed partitions can reduce the risk of cross-contamination while bad designs may increase the risk in some locations) (Rooney et al. 2021)	Personal environment	US$100/m^2 material	Long-term use	Easy
	Cubicle workstation	Reducing cross-contamination between cubicles with typical ventilation effectiveness of 1.1 to 3.6 (require well-designed ventilation and air distribution) (Haghighat et al. 1996)	Personal environment	US$2000 for a 2 × 2 m cubicle	Long-term use	Need professional design and installation (incorporating with ventilation)
	Enclosed/semi-enclosed modular office walls	Enclosed modular office walls can fully avoid cross-contamination between modular spaces (require sufficient ventilation supplied to each space)	Personal environment	US$3000 for a 2 × 2 m seat	Long-term use	Need professional design and installation (incorporating with ventilation)
Air cleaning and disinfection	Upper-room UVGI system	Proper use can largely improve the inactivation rate of virus (e.g. 16 h^−1 for M. parafortuitum)^i	Room	US$1200–2500 (US$40–90/m^2 floor area) (VirusLights 2021)	Long-term use	Need professional design and installation (incorporating with ventilation)
	Portable air cleaners	Typically supplying 361 m^3/h CADR (median CADR from a market survey (B. Zhao, Liu, and Chen 2020))	Room	US$493/count (i.e. US$1.32 per m^3/h CADR, median price from a market survey (B. Zhao, Liu, and Chen 2020)) (less than US$50/count for HEPA filter replacement)	Long-term use (filters need regular replacement)	Easy; Potential emissions should be considered (some air cleaners can generate hazardous emissions like ozone (Guo, Gao, and Shen 2019))
	Sunlight	Increasing the natural inactivation of SARS-CoV-2 on aerosols (decay rate: <1 h^−1 without sunlight, >7 h^−1 with low-intensity sunlight, >18 h^−1 with high-intensity sunlight)	Room	US$0^j	Long-term use	Depending on weather conditions and building design^k
Occupancy control	Occupancy density restriction (limiting occupant number and social distance in the building/room^m)	Reducing the potential emissions of pathogens to the air and reducing the risk of cross-contamination	Building/room	US$0^l	Long-term use	Easy (need to coordinate with occupant schedules)
	Intermittent occupancy (A. K. Melikov, Ai, and Markov 2020) or staggered scheduling (U.S. CDC 2021j)	Reducing the potential emissions of pathogens to the air and decreasing the pathogen inhalation by the susceptible people (e.g. asking students to leave the classroom during the 15 min break after a 35 min class can reduce 35% inhaled pathogen (A. K. Melikov, Ai, and Markov 2020))	Building/room	US$0	Long-term use	Easy (need to coordinate with occupant schedules)

^a Capital costs are approximately estimated based on a brief market survey in the U.S. (data obtained from search results on Google). The actual costs may vary a lot in other countries or regions.

^b The strategy can be accessed easily through in-store/online purchase or easy operation.

^c Surgical and N95 masks are designed for disposable use but can be reused a couple of times after decontamination under certain conditions (U.S. CDC 2021e).

^d N95 masks can generally fit better than cloth and surgical masks. Proper use of N95 masks can minimize air leakage through gaps.

^e Other strategies that can maximize fit for surgical masks include (1) covering the surgical mask with a cloth mask, and (2) knotting ear loops of the surgical mask, which can improve the particle filtration efficiency to around 80% (Brooks et al. 2021).

^f Long-term use indicates a duration of typically over one year.

^g The annual average cost of air conditioning with central and individual units in the U.S. is US$0.31 and US$0.15 per square foot, respectively (U.S. EIA 2018). Assuming the outdoor air fraction of the HVAC system is 25%, applying 100% outdoor air will simply cost 3× more energy for pre-heating or pre-cooling the extra outdoor air.

^h It can improve the natural ventilation efficiency and introduce more outdoor air to the room incorporating fans.

ⁱ The effectiveness of virus inactivation by the upper-room UVGI system also relies on room air distribution. Displacement ventilation may reduce the efficiency as it decreases the residence time of the virus in the irradiated zone (Kanaan and Abou Moughlbay 2018).

^j Introducing more sunlight to the room may impact the heating and cooling energy consumption for the HVAC system.

^k Building design like window/wall ratio and building geometry can impact the incident sunlight.

^l The potential economic loss due to occupancy restriction is not considered.

m The safe social distance is recommended as 1.6–3.0 m considering the aerosol transmission of exhaled large droplets from talking (Sun and Zhai 2020).

WHO. 2021a. WHO Coronavirus Disease (COVID-19) Dashboard | WHO Coronavirus Disease (COVID-19) Dashboard.

 Google Scholar

Google. 2020. COVID airborne – explore – Google Trends.

 Google Scholar

Choi, H., and H. Varian. 2012. Predicting the present with google trends. Economic Record 88 (Suppl.1):2–9. doi:https://doi.org/10.1111/j.1475-4932.2012.00809.x

 Google Scholar

Binder, R. A., N. A. Alarja, E. R. Robie, K. E. Kochek, L. Xiu, L. Rocha-Melogno, A. Abdelgadir, S. V. Goli, A. S. Farrell, K. K. Coleman, et al. 2020. Environmental and aerosolized severe acute respiratory syndrome coronavirus 2 among hospitalized coronavirus disease 2019 patients. The Journal of Infectious Diseases 222 (11):1798–806. doi:https://doi.org/10.1093/infdis/jiaa575

 PubMed Web of Science ®Google Scholar

Cheng, V. C. C., S. C. Wong, J. H. K. Chen, C. C. Y. Yip, V. W. M. Chuang, O. T. Y. Tsang, S. Sridhar, J. F. W. Chan, P. L. Ho, and K. Y. Yuen. 2020b. Escalating infection control response to the rapidly evolving epidemiology of the coronavirus disease 2019 (COVID-19) due to SARS-CoV-2 in Hong Kong. Infection Control & Hospital Epidemiology 41 (5):493–8. doi:https://doi.org/10.1017/ice.2020.58

 PubMed Web of Science ®Google Scholar

Chia, P. Y., K. K. Coleman, Y. K. Tan, S. W. X. Ong, M. Gum, S. K. Lau, S. Sutjipto, P. H. Lee, T. T. Son, B. E. Young, et al. 2020a. Detection of air and surface contamination by severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) in hospital rooms of infected patients. MedRxiv.

 Google Scholar

de Man, P., S. Paltansing, D. S. Y. Ong, N. Vaessen, G. van Nielen, and J. G. M. Koeleman. 2020. Outbreak of Coronavirus Disease 2019 (COVID-19) in a nursing home associated with aerosol transmission as a result of inadequate ventilation. Clinical Infectious Diseases 73 (1):170–171.

 Google Scholar

Ding, Z., H. Qian, B. Xu, Y. Huang, T. Miao, H. L. Yen, S. Xiao, L. Cui, X. Wu, W. Shao, et al. 2021. Toilets dominate environmental detection of severe acute respiratory syndrome coronavirus 2 in a hospital. Science of the Total Environment 753:141710. doi:https://doi.org/10.1016/j.scitotenv.2020.141710

 PubMed Web of Science ®Google Scholar

Döhla, M., G. Wilbring, B. Schulte, B. M. Kümmerer, C. Diegmann, E. Sib, E. Richter, A. Haag, S. Engelhart, A. M. Eis-Hübinger, et al. 2020. SARS-CoV-2 in environmental samples of quarantined households. MedRxiv.

 Google Scholar

Dunker, S., T. Hornick, G. Szczepankiewicz, M. Maier, M. Bastl, J. Bumberger, R. Treudler, U. G. Liebert, and J.-C. Simon. 2021. No SARS-CoV-2 detected in air samples (pollen and particulate matter) in Leipzig during the first spread. Science of the Total Environment 755:142881. doi:https://doi.org/10.1016/j.scitotenv.2020.142881

 PubMed Web of Science ®Google Scholar

Faridi, S., S. Niazi, K. Sadeghi, K. Naddafi, J. Yavarian, M. Shamsipour, N. Z. S. Jandaghi, K. Sadeghniiat, R. Nabizadeh, M. Yunesian, et al. 2020. A field indoor air measurement of SARS-CoV-2 in the patient rooms of the largest hospital in Iran. Science of the Total Environment 725:138401. doi:https://doi.org/10.1016/j.scitotenv.2020.138401

 PubMed Web of Science ®Google Scholar

Feng, B., K. Xu, S. Gu, S. Zheng, Q. Zou, Y. Xu, L. Yu, F. Lou, F. Yu, T. Jin, et al. 2021. Multi-route transmission potential of SARS-CoV-2 in healthcare facilities. Journal of Hazardous Materials 402:123771. doi:https://doi.org/10.1016/j.jhazmat.2020.123771

 PubMed Web of Science ®Google Scholar

Guo, Z. D., Z. Y. Wang, S. F. Zhang, X. Li, L. Li, C. Li, Y. Cui, R. B. Fu, Y. Z. Dong, X. Y. Chi, et al. 2020. Aerosol and surface distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards, Wuhan, China, 2020. Emerging Infectious Diseases 26 (7):1586–91. doi:https://doi.org/10.3201/eid2607.200885

 Web of Science ®Google Scholar

Hadei, M., S. R. Mohebbi, P. K. Hopke, A. Shahsavani, S. Bazzazpour, M. Alipour, A. J. Jafari, A. M. Bandpey, A. Zali, M. Yarahmadi, et al. 2021. Presence of SARS-CoV-2 in the air of public places and transportation. Atmospheric Pollution Research 12 (3):302–6. doi:https://doi.org/10.1016/j.apr.2020.12.016

 PubMed Web of Science ®Google Scholar

Horve, P. F., L. Dietz, M. Fretz, D. A. Constant, A. Wilkes, J. M. Townes, R. G. Martindale, W. B. Messer, and K. G. van Den Wymelenberg. 2020. Identification of SARS-CoV-2 RNA in healthcare heating, ventilation, and air conditioning units. MedRxiv.

 Google Scholar

Jiang, Y., H. Wang, Y. Chen, J. He, L. Chen, Y. Liu, X. Hu, A. Li, S. Liu, P. Zhang, et al. 2020. Clinical data on hospital environmental hygiene monitoring and medical staff protection during the Coronavirus disease 2019 outbreak. MedRxiv.

 Google Scholar

Jin, T., J. Li, J. Yang, J. Li, F. Hong, H. Long, Q. Deng, Y. Qin, J. Jiang, X. Zhou, et al. 2021. SARS-CoV-2 presented in the air of an intensive care unit (ICU). Sustainable Cities and Society 65:102446. doi:https://doi.org/10.1016/j.scs.2020.102446

 PubMed Web of Science ®Google Scholar

Kenarkoohi, A., Z. Noorimotlagh, S. Falahi, A. Amarloei, S. A. Mirzaee, I. Pakzad, and E. Bastani. 2020. Hospital indoor air quality monitoring for the detection of SARS-CoV-2 (COVID-19) virus. Science of the Total Environment 748:141324. doi:https://doi.org/10.1016/j.scitotenv.2020.141324

 PubMed Web of Science ®Google Scholar

Kim, J. Y., J.-H. Ko, Y. Kim, Y.-J. Kim, J.-M. Kim, Y.-S. Chung, H. M. Kim, M.-G. Han, S. Y. Kim, and B. S. Chin. 2020. Viral load kinetics of SARS-CoV-2 infection in first two patients in Korea. Journal of Korean Medical Science 35 (7):e86.

 PubMed Web of Science ®Google Scholar

Lane, M. A., E. A. Brownsword, J. S. Morgan, A. Babiker, S. A. Vanairsdale, G. M. Lyon, A. K. Mehta, J. M. Ingersoll, W. G. Lindsley, and C. S. Kraft. 2020. Bioaerosol sampling of a ventilated patient with COVID-19. American Journal of Infection Control 48 (12):1540–2. doi:https://doi.org/10.1016/j.ajic.2020.07.033

 PubMed Web of Science ®Google Scholar

Lednicky, J. A., M. Lauzard, Z. H. Fan, A. Jutla, T. B. Tilly, M. Gangwar, M. Usmani, S. N. Shankar, K. Mohamed, A. Eiguren-Fernandez, et al. 2020. Viable SARS-CoV-2 in the air of a hospital room with COVID-19 patients. International Journal of Infectious Diseases: IJID 100:476–82. doi:https://doi.org/10.1016/j.ijid.2020.09.025

 PubMed Web of Science ®Google Scholar

Lednicky, J. A., M. Lauzardo, M. M. Alam, M. A. Elbadry, C. J. Stephenson, J. C. Gibson, and J. G. Morris. 2021. Isolation of SARS-CoV-2 from the air in a car driven by a COVID patient with mild illness. MedRxiv 2021.01.12.21249603.

 Google Scholar

Li, Y., H. Qian, J. Hang, X. Chen, L. Hong, P. Liang, J. Li, S. Xiao, J. Wei, L. Liu, et al. 2020. Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated restaurant. MedRxiv 2020.04.16.20067728.

 Google Scholar

Liu, Y., Z. Ning, Y. Chen, M. Guo, Y. Liu, N. K. Gali, L. Sun, Y. Duan, J. Cai, D. Westerdahl, et al. 2020. Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature 582 (7813):557–560. doi:https://doi.org/10.1038/s41586-020-2271-3

 PubMed Web of Science ®Google Scholar

Ma, J., X. Qi, H. Chen, X. Li, Z. Zhang, H. Wang, L. Sun, L. Zhang, J. Guo, L. Morawska, et al. 2020. Coronavirus disease 2019 patients in earlier stages exhaled millions of severe acute respiratory syndrome coronavirus 2 per hour. Clinical Infectious Diseases 72 (10):e652–e654.

 Web of Science ®Google Scholar

Maestre, J. P., D. Jarma, J. R. F. Yu, J. A. Siegel, S. D. Horner, and K. A. Kinney. 2021. Distribution of SARS-CoV-2 RNA signal in a home with COVID-19 positive occupants. Science of the Total Environment 778:146201. doi:https://doi.org/10.1016/j.scitotenv.2021.146201

 PubMed Web of Science ®Google Scholar

Masoumbeigi, H., G. Ghanizadeh, R. Yousefi Arfaei, S. Heydari, H. Goodarzi, R. Dorostkar Sari, and M. Tat. 2020. Investigation of hospital indoor air quality for the presence of SARS-Cov-2. Journal of Environmental Health Science and Engineering 18 (2):1259–1263. doi:https://doi.org/10.1007/s40201-020-00543-3

 Web of Science ®Google Scholar

Moore, G., H. Rickard, D. Stevenson, P. Aranega-Bou, J. Pitman, A. Crook, K. Davies, A. Spencer, C. Burton, L. Easterbrook, et al. 2021. Detection of SARS-CoV-2 within the healthcare environment: A multi-centre study conducted during the first wave of the COVID-19 outbreak in England. Journal of Hospital Infection 108:189–196. doi:https://doi.org/10.1016/j.jhin.2020.11.024

 PubMedGoogle Scholar

Moreno, T., R. M. Pintó, A. Bosch, N. Moreno, A. Alastuey, M. C. Minguillón, E. Anfruns-Estrada, S. Guix, C. Fuentes, G. Buonanno, et al. 2021. Tracing surface and airborne SARS-CoV-2 RNA inside public buses and subway trains. Environment International 147:106326. doi:https://doi.org/10.1016/j.envint.2020.106326

 PubMed Web of Science ®Google Scholar

Mouchtouri, V. A., M. Koureas, M. Kyritsi, A. Vontas, L. Kourentis, S. Sapounas, G. Rigakos, E. Petinaki, S. Tsiodras, and C. Hadjichristodoulou. 2020. Environmental contamination of SARS-CoV-2 on surfaces, air-conditioner and ventilation systems. International Journal of Hygiene and Environmental Health 230:113599. doi:https://doi.org/10.1016/j.ijheh.2020.113599

 PubMed Web of Science ®Google Scholar

Nissen, K., J. Krambrich, D. Akaberi, T. Hoffman, J. Ling, Å. Lundkvist, L. Svensson, and E. Salaneck. 2020. Long-distance airborne dispersal of SARS-CoV-2 in COVID-19 wards. Scientific Reports 10 (1):19589–9. doi:https://doi.org/10.1038/s41598-020-76442-2

 PubMed Web of Science ®Google Scholar

Ong, S. W. X., Y. K. Tan, P. Y. Chia, T. H. Lee, O. T. Ng, M. S. Y. Wong, and K. Marimuthu. 2020. Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient. JAMA 323 (16):1610. doi:https://doi.org/10.1001/jama.2020.3227

 PubMed Web of Science ®Google Scholar

Razzini, K., M. Castrica, L. Menchetti, L. Maggi, L. Negroni, N. V. Orfeo, A. Pizzoccheri, M. Stocco, S. Muttini, and C. M. Balzaretti. 2020. SARS-CoV-2 RNA detection in the air and on surfaces in the COVID-19 ward of a hospital in Milan, Italy. Science of the Total Environment 742:140540. doi:https://doi.org/10.1016/j.scitotenv.2020.140540

 PubMed Web of Science ®Google Scholar

Santarpia, J. L., D. N. Rivera, V. L. Herrera, M. J. Morwitzer, H. M. Creager, G. W. Santarpia, K. K. Crown, D. M. Brett-Major, E. R. Schnaubelt, M. J. Broadhurst, et al. 2020. Aerosol and surface contamination of SARS-CoV-2 observed in quarantine and isolation care. Scientific Reports 10 (1):12732. doi:https://doi.org/10.1038/s41598-020-69286-3

 PubMed Web of Science ®Google Scholar

Setti, L., F. Passarini, G. De Gennaro, P. Barbieri, M. G. Perrone, M. Borelli, J. Palmisani, A. D. Gilio, P. Piscitelli, and A. Miani. 2020a. Airborne transmission route of COVID-19: Why 2 meters/6 feet of inter-personal distance could not be enough. International Journal of Environmental Research and Public Health 17 (8):2932. doi:https://doi.org/10.3390/ijerph17082932

 PubMed Web of Science ®Google Scholar

Stern, R. A., P. Koutrakis, M. A. G. Martins, B. Lemos, S. E. Dowd, E. M. Sunderland, and E. Garshick. 2021. Characterization of hospital airborne SARS-CoV-2. Respiratory Research 22 (1):1–8. doi:https://doi.org/10.1186/s12931-021-01637-8

 PubMed Web of Science ®Google Scholar

Tan, L., B. Ma, X. Lai, L. Han, P. Cao, J. Zhang, J. Fu, Q. Zhou, S. Wei, Z. Wang, et al. 2020. Air and surface contamination by SARS-CoV-2 virus in a tertiary hospital in Wuhan, China. International Journal of Infectious Diseases 99:3–7. doi:https://doi.org/10.1016/j.ijid.2020.07.027

 PubMed Web of Science ®Google Scholar

Zhou, L., M. Yao, X. Zhang, B. Hu, X. Li, H. Chen, L. Zhang, Y. Liu, M. Du, B. Sun, et al. 2021. Breath-, air- and surface-borne SARS-CoV-2 in hospitals. Journal of Aerosol Science 152:105693. doi:https://doi.org/10.1016/j.jaerosci.2020.105693

 PubMed Web of Science ®Google Scholar

Dabisch, P., M. Schuit, A. Herzog, K. Beck, S. Wood, M. Krause, D. Miller, W. Weaver, D. Freeburger, I. Hooper, et al. 2020. The influence of temperature, humidity, and simulated sunlight on the infectivity of SARS-CoV-2 in aerosols. Aerosol Science and Technology 55 (2):142–53.

 Web of Science ®Google Scholar

Fears, A. C., W. B. Klimstra, P. Duprex, A. Hartman, S. C. Weaver, K. S. Plante, D. Mirchandani, J. A. Plante, P. V. Aguilar, D. Fernández, et al. 2020. Persistence of severe acute respiratory syndrome coronavirus 2 in aerosol suspensions. Emerging Infectious Diseases 26 (9):2168–71. doi:https://doi.org/10.3201/eid2609.201806

 Web of Science ®Google Scholar

Schuit, M., S. Ratnesar-Shumate, J. Yolitz, G. Williams, W. Weaver, B. Green, D. Miller, M. Krause, K. Beck, S. Wood, et al. 2020. Airborne SARS-CoV-2 is rapidly inactivated by simulated sunlight. The Journal of Infectious Diseases 222 (4):564–71. doi:https://doi.org/10.1093/infdis/jiaa334

 PubMed Web of Science ®Google Scholar

Smither, S. J., L. S. Eastaugh, J. S. Findlay, and M. S. Lever. 2020. Experimental aerosol survival of SARS-CoV-2 in artificial saliva and tissue culture media at medium and high humidity. Emerging Microbes and Infections 9 (1):1415–17.

 PubMed Web of Science ®Google Scholar

van Doremalen, N., T. Bushmaker, D. H. Morris, M. G. Holbrook, A. Gamble, B. N. Williamson, A. Tamin, J. L. Harcourt, N. J. Thornburg, S. I. Gerber, et al. 2020. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. New England Journal of Medicine 382 (16):1564–7. doi:https://doi.org/10.1056/NEJMc2004973

 PubMed Web of Science ®Google Scholar

Almilaji, O., and P. Thomas. 2020. Air recirculation role in the infection with COVID-19, lessons learned from Diamond Princess Cruise ship. MedRxiv 2020.07.08.20148775.

 Google Scholar

Azimi, P., Z. Keshavarz, J. G. Cedeno Laurent, B. Stephens, and J. G. Allen. 2021. Mechanistic transmission modeling of COVID-19 on the Diamond Princess Cruise ship demonstrates the importance of aerosol transmission. Proceedings of the National Academy of Sciences 118 (8):e2015482118. doi:https://doi.org/10.1073/pnas.2015482118

 PubMed Web of Science ®Google Scholar

Buonanno, G., L. Morawska, and L. Stabile. 2020. Quantitative assessment of the risk of airborne transmission of SARS-CoV-2 infection: Prospective and retrospective applications. Environment International 145:106112. doi:https://doi.org/10.1016/j.envint.2020.106112

 PubMed Web of Science ®Google Scholar

Cai, J., W. Sun, J. Huang, M. Gamber, J. Wu, and G. He. 2020. Indirect virus transmission in cluster of COVID-19 cases, Wenzhou, China, 2020. Emerging Infectious Diseases 26 (6):1343–5. doi:https://doi.org/10.3201/eid2606.200412

 PubMed Web of Science ®Google Scholar

Chau, N. V. V., N. T. T. Hong, N. M. Ngoc, T. T. Thanh, P. N. Q. Khanh, L. A. Nguyet, L. N. T. Nhu, N. T. H. Ny, D. N. H. Man, V. T. T. Hang, et al. 2021. Superspreading event of SARS-CoV-2 infection at a bar, Ho Chi Minh city, Vietnam. Emerging Infectious Diseases 27 (1):310–4. doi:https://doi.org/10.3201/eid2701.203480

 Web of Science ®Google Scholar

Crema, E. 2021. The SARS-COV-2 outbreak around the Amazon rainforest: The relevance of the airborne transmission. Science of the Total Environment 759:144312. doi:https://doi.org/10.1016/j.scitotenv.2020.144312

 PubMed Web of Science ®Google Scholar

Eichler, N., C. Thornley, T. Swadi, T. Devine, C. McElnay, J. Sherwood, C. Brunton, F. Williamson, J. Freeman, S. Berger, et al. 2021. Transmission of severe acute respiratory syndrome coronavirus 2 during border quarantine and air travel, New Zealand (Aotearoa). Emerging Infectious Diseases 27 (5):1274–8. doi:https://doi.org/10.3201/eid2705.210514

 PubMed Web of Science ®Google Scholar

Günther, T., M. Czech, ‐D. Sioli, A. Indenbirken, P. Robitaille, M. Tenhaken, M. Exner, N. Ottinger, A. Fischer, M. M. Grundhoff, et al. 2020. SARS‐CoV‐2 outbreak investigation in a German meat processing plant. EMBO Molecular Medicine 12 (12):e13296. doi:https://doi.org/10.15252/emmm.202013296

 PubMed Web of Science ®Google Scholar

Hwang, S. E., J. H. Chang, B. Oh, and J. Heo. 2021. Possible aerosol transmission of COVID-19 associated with an outbreak in an apartment in Seoul, South Korea, 2020. International Journal of Infectious Diseases 104:73–6. doi:https://doi.org/10.1016/j.ijid.2020.12.035

 PubMed Web of Science ®Google Scholar

Kang, M., J. Wei, J. Yuan, J. Guo, Y. Zhang, J. Hang, Y. Qu, H. Qian, Y. Zhuang, X. Chen, et al. 2020. Probable evidence of fecal aerosol transmission of SARS-CoV-2 in a high-rise building. Annals of Internal Medicine 173 (12):974–80. doi:https://doi.org/10.7326/M20-0928

 PubMed Web of Science ®Google Scholar

Katelaris, A. L., J. Wells, P. Clark, S. Norton, R. Rockett, A. Arnott, V. Sintchenko, S. Corbett, and S. K. Bag. 2021. Epidemiologic evidence for airborne transmission of SARS-CoV-2 during Church Singing, Australia, 2020. Emerging Infectious Diseases 27 (6):1677–80. doi:https://doi.org/10.3201/eid2706.210465

 PubMed Web of Science ®Google Scholar

Khanh, N. C., P. Q. Thai, H. L. Quach, N. A. H. Thi, P. C. Dinh, T. N. Duong, L. T. Q. Mai, N. D. Nghia, T. A. Tu, L. N. Quang, et al. 2020. Transmission of SARS-CoV 2 during long-haul flight. Emerging Infectious Diseases 26 (11):2617–24. doi:https://doi.org/10.3201/eid2611.203299

 PubMed Web of Science ®Google Scholar

Luo, K., Z. Lei, Z. Hai, S. Xiao, J. Rui, H. Yang, X. Jing, H. Wang, Z. Xie, P. Luo, et al. 2020. Transmission of SARS-CoV-2 in public transportation vehicles: A case study in Hunan Province, China. Open Forum Infectious Diseases 7 (10):ofaa430. doi:https://doi.org/10.1093/ofid/ofaa430

 PubMed Web of Science ®Google Scholar

Miller, S. L., W. W. Nazaroff, J. L. Jimenez, A. Boerstra, G. Buonanno, S. J. Dancer, J. Kurnitski, L. C. Marr, L. Morawska, and C. Noakes. 2020. Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event. MedRxiv (June):2020.06.15.20132027.

 Google Scholar

Shen, Y., C. Li, H. Dong, Z. Wang, L. Martinez, Z. Sun, A. Handel, Z. Chen, E. Chen, M. H. Ebell, et al. 2020. Community outbreak investigation of SARS-CoV-2 transmission among bus riders in Eastern China. JAMA Internal Medicine 180 (12):1665. doi:https://doi.org/10.1001/jamainternmed.2020.5225

 PubMed Web of Science ®Google Scholar

Tang, S., Y. Mao, R. M. Jones, Q. Tan, J. S. Ji, N. Li, J. Shen, Y. Lv, L. Pan, P. Ding, et al. 2020. Aerosol transmission of SARS-CoV-2? Evidence, prevention and control. Environment International 144:106039. doi:https://doi.org/10.1016/j.envint.2020.106039

 PubMed Web of Science ®Google Scholar

Wang, J., and G. Du. 2020. COVID-19 may transmit through aerosol. Irish Journal of Medical Science 189 (4):1143–4. doi:https://doi.org/10.1007/s11845-020-02218-2

 PubMed Web of Science ®Google Scholar

Zhang, R., Y. Li, A. L. Zhang, Y. Wang, and M. J. Molina. 2020. Identifying airborne transmission as the dominant route for the spread of COVID-19. Proceedings of the National Academy of Sciences of the United States of America 117 (26):14857–63.

 PubMed Web of Science ®Google Scholar

Kim, Y. I., S. G. Kim, S. M. Kim, E. H. Kim, S. J. Kim, K. M. Park, J. H. Yu, E. J. Chang, S. Kim, M. A. B. Lee, et al. 2020. Infection and rapid transmission of SARS-CoV-2 in ferrets. Cell Host & Microbe 27 (5):704-9.e2. doi:https://doi.org/10.1016/j.chom.2020.03.023

 Web of Science ®Google Scholar

Kutter, J. S., D. de Meulder, T. M. Bestebroer, P. Lexmond, A. Mulders, M. Richard, R. A. M. Fouchier, and S. Herfst. 2021. SARS-CoV and SARS-CoV-2 are transmitted through the air between ferrets over more than one meter distance. Nature Communications 12 (1):1–8. doi:https://doi.org/10.1038/s41467-021-21918-6

 PubMed Web of Science ®Google Scholar

Richard, M., A. Kok, D. de Meulder, T. M. Bestebroer, M. M. Lamers, N. M. A. Okba, M. Fentener van Vlissingen, B. Rockx, B. L. Haagmans, M. P. G. Koopmans, et al. 2020. SARS-CoV-2 is transmitted via contact and via the air between ferrets. Nature Communications 11 (1):1–6. doi:https://doi.org/10.1038/s41467-020-17367-2

 PubMed Web of Science ®Google Scholar

Shi, J., Z. Wen, G. Zhong, H. Yang, C. Wang, B. Huang, R. Liu, X. He, L. Shuai, Z. Sun, et al. 2020. Susceptibility of ferrets, cats, dogs, and other domesticated animals to SARS-coronavirus 2. Science (New York, N.Y.) 368 (6494):1016–20. doi:https://doi.org/10.1126/science.abb7015

 PubMed Web of Science ®Google Scholar

Morawska, L., G. R. Johnson, Z. D. Ristovski, M. Hargreaves, K. Mengersen, S. Corbett, C. Y. H. Chao, Y. Li, and D. Katoshevski. 2009. Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. Journal of Aerosol Science 40 (3):256–269. doi:https://doi.org/10.1016/j.jaerosci.2008.11.002

 Web of Science ®Google Scholar

Chia, P. Y., K. K. Coleman, Y. K. Tan, S. W. X. Ong, M. Gum, S. K. Lau, X. F. Lim, A. S. Lim, S. Sutjipto, P. H. Lee, et al. 2020b. Detection of air and surface contamination by SARS-CoV-2 in hospital rooms of infected patients. Nature Communications 11 (1):1–7. doi:https://doi.org/10.1038/s41467-020-16670-2

 PubMed Web of Science ®Google Scholar

Feng, Z., F. Wei, H. Li, and C. W. Yu. 2021. Evaluation of indoor disinfection technologies for airborne disease control in hospital. Indoor and Built Environment 30 (6):727–31. doi:https://doi.org/10.1177/1420326X211002948

 Web of Science ®Google Scholar

CDPHE. 2020. Outbreak data | Colorado COVID-19 Updates.

 Google Scholar

MDHHS. 2020. Coronavirus – outbreak reporting.

 Google Scholar

Shen, J., M. Kong, B. Dong, M. J. Birnkrant, and J. Zhang. 2021. A systematic approach to estimating the effectiveness of multi-scale IAQ strategies for reducing the risk of airborne infection of SARS-CoV-2. Building and Environment 200:107926. doi:https://doi.org/10.1016/j.buildenv.2021.107926

 PubMed Web of Science ®Google Scholar

Bazant, M. Z., O. Kodio, A. E. Cohen, K. Khan, Z. Gu, and J. W. M. Bush. 2021. Monitoring carbon dioxide to quantify the risk of indoor airborne transmission of COVID-19. MedRxiv 2021.04.04.21254903.

 Google Scholar

Buonanno, G., L. Stabile, and L. Morawska. 2020. Estimation of airborne viral emission: Quanta emission rate of SARS-CoV-2 for infection risk assessment. Environment International 141:105794. doi:https://doi.org/10.1016/j.envint.2020.105794

 PubMed Web of Science ®Google Scholar

Chen, L., G. Ban, E. Long, G. Kalonji, Z. Cheng, L. Zhang, and S. Guo. 2021. Estimation of the SARS-CoV-2 transmission probability in confined traffic space and evaluation of the mitigation strategies. Environmental Science and Pollution Research 28:42204–16.

 PubMed Web of Science ®Google Scholar

Dai, H., and B. Zhao. 2020b. Association of the infection probability of COVID-19 with ventilation rates in confined spaces. Building Simulation 13 (6):1321–7. doi:https://doi.org/10.1007/s12273-020-0703-5

 PubMed Web of Science ®Google Scholar

Harrichandra, A., A. M. Ierardi, and B. Pavilonis. 2020. An estimation of airborne SARS-CoV-2 infection transmission risk in New York City nail salons. Toxicology and Industrial Health 36 (9):634–43.

 PubMed Web of Science ®Google Scholar

Zhang, S., and Z. Lin. 2020. Dilution-based evaluation of airborne infection risk-thorough expansion of Wells-Riley model 2 running head: Thorough expansion of Wells-Riley model. MedRxiv 2020.10.03.20206391.

 Google Scholar

Konda, A., A. Prakash, G. A. Moss, M. Schmoldt, G. D. Grant, and S. Guha. 2020. Aerosol filtration efficiency of common fabrics used in respiratory cloth masks. ACS Nano 14 (5):6339–47. doi:https://doi.org/10.1021/acsnano.0c03252

 PubMed Web of Science ®Google Scholar

Zhao, M., L. Liao, W. Xiao, X. Yu, H. Wang, Q. Wang, Y. L. Lin, F. S. Kilinc-Balci, A. Price, L. Chu, et al. 2020. Household materials selection for homemade cloth face coverings and their filtration efficiency enhancement with triboelectric charging. Nano Letters 20 (7):5544–52. doi:https://doi.org/10.1021/acs.nanolett.0c02211

 PubMed Web of Science ®Google Scholar

Davies, A., K.-A. Thompson, K. Giri, G. Kafatos, J. Walker, and A. Bennett. 2013. Testing the efficacy of homemade masks: Would they protect in an influenza pandemic? Disaster Medicine and Public Health Preparedness 7:413–8.

 PubMed Web of Science ®Google Scholar

Rothamer, D. A., S. Sanders, D. Reindl, T. H. Bertram, and D. Rothamer. 2020. Strategies to minimize SARS-CoV-2 transmission in classroom settings: Combined impacts of ventilation and mask effective filtration efficiency. MedRxiv 2020.12.31.20249101.

 Google Scholar

U.S. CDC. 2021d. COVID-19: Strategies for optimizing the supply of PPE | CDC.

 Google Scholar

Lindsley, W. G., J. D. Noti, F. M. Blachere, J. V. Szalajda, and D. H. Beezhold. 2014. Efficacy of face shields against cough aerosol droplets from a cough simulator. Journal of Occupational and Environmental Hygiene 11 (8):509–518. doi:https://doi.org/10.1080/15459624.2013.877591

 PubMed Web of Science ®Google Scholar

UW Madison. 2020. Badger Seal (Mask Fitter, Mask Sealer, Mask Brace).

 Google Scholar

Fix The Mask. 2020. DIY Mask Brace from Rubber Sheet Downloadable Template – Fix The Mask.

 Google Scholar

Risbeck, M. J., M. Z. Bazant, Z. Jiang, Y. M. Lee, K. H. Drees, and J. D. Douglas. 2021. Quantifying the tradeoff between energy consumption and the risk of airborne disease transmission for building HVAC systems. MedRxiv 2021.06.21.21259287.

 Google Scholar

U.S. EIA. 2018. Air conditioning accounts for about 12% of U.S. home energy expenditures – Today in Energy – U.S. Energy Information Administration (EIA).

 Google Scholar

Melikov, A., H. Grønbaek, and J. B. Nielsen. 2007. Personal Ventilation: From research to practical use.

 Google Scholar

Dygert, R. K., and T. Q. Dang. 2012. Experimental validation of local exhaust strategies for improved IAQ in aircraft cabins. Building and Environment 47 (1):76–88. doi:https://doi.org/10.1016/j.buildenv.2011.04.025

 Google Scholar

Chen, Q., and L. Glicksman. 2003. System performance evaluation and design guidelines for displacement ventilation. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers.

 Google Scholar

Qian, H., Y. Li, W. H. Seto, P. Ching, W. H. Ching, and H. Q. Sun. 2010. Natural ventilation for reducing airborne infection in hospitals. Building and Environment 45 (3):559–65. doi:https://doi.org/10.1016/j.buildenv.2009.07.011

 PubMed Web of Science ®Google Scholar

Rooney, C. M., J. McIntyre, L. Ritchie, and M. H. Wilcox. 2021. Evidence review of physical distancing and partition screens to reduce healthcare acquired SARS-CoV-2. Infection Prevention in Practice 3 (2):100144. doi:https://doi.org/10.1016/j.infpip.2021.100144

 PubMedGoogle Scholar

Haghighat, F., Y. Huo, J. Zhang, and C. Shaw. 1996. The influence of office furniture, workstation layouts, diffuser types and location on indoor air quality and thermal comfort conditions at workstations. Indoor Air 6 (3):188–203. doi:https://doi.org/10.1111/j.1600-0668.1996.t01-1-00006.x

 Web of Science ®Google Scholar

VirusLights. 2021. LIGHTDIS upper air fixtures – viruslights.

 Google Scholar

Zhao, B., Y. Liu, and C. Chen. 2020. Air purifiers: A supplementary measure to remove airborne SARS-CoV-2. Building and Environment 177:106918. doi:https://doi.org/10.1016/j.buildenv.2020.106918

 PubMed Web of Science ®Google Scholar

Guo, C., Z. Gao, and J. Shen. 2019. Emission rates of indoor ozone emission devices: A literature review. Building and Environment 158:302–18. doi:https://doi.org/10.1016/j.buildenv.2019.05.024

 Web of Science ®Google Scholar

Melikov, A. K., Z. T. Ai, and D. G. Markov. 2020. Intermittent occupancy combined with ventilation: An efficient strategy for the reduction of airborne transmission indoors. Science of the Total Environment 744:140908. doi:https://doi.org/10.1016/j.scitotenv.2020.140908

 PubMed Web of Science ®Google Scholar

U.S. CDC. 2021j. Operational Strategy for K-12 Schools through Phased Prevention | CDC.

 Google Scholar

U.S. CDC. 2021e. COVID-19 decontamination and reuse of filtering facepiece respirators | CDC.

 Google Scholar

Brooks, J. T., D. H. Beezhold, J. D. Noti, J. P. Coyle, R. C. Derk, F. M. Blachere, and W. G. Lindsley. 2021. Maximizing fit for cloth and medical procedure masks to improve performance and reduce SARS-CoV-2 transmission and exposure, 2021. MMWR. Morbidity and Mortality Weekly Report 70 (7):254–7. doi:https://doi.org/10.15585/mmwr.mm7007e1

 PubMed Web of Science ®Google Scholar

Kanaan, M., and A. Abou Moughlbay. 2018. Comparative CFD investigation of upper room UVGI efficacy with three different ventilation systems. International Journal of Applied Engineering Research 13 (12):14897–14902.

 Google Scholar

Sun, C., and Z. Zhai. 2020. The efficacy of social distance and ventilation effectiveness in preventing COVID-19 transmission. Sustainable Cities and Society 62:102390. doi:https://doi.org/10.1016/j.scs.2020.102390

 PubMed Web of Science ®Google Scholar

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.