4.1a Droplets & aerosols

Droplets: small liquid drops that are generated by expiratory events such as coughing, sneezing, laughing, talking or even breathing. 

• Large droplets: usually brought down to ground under gravity and are transmitted over a limited distance (0.3-1.0 m).
• Small droplets: water content of large droplets may evaporate in air, producing smaller droplet that could travel up to 1.5 m.
• Droplet nuclei: water content of small droplets may evaporate in air, producing even smaller droplet nuclei that could then remain suspended in air and could be transmitted over a long distance (up to 50 m).

Aerosols: Suspensions of small liquid droplets or solid particles in air. 

4.1b Fomites

(1) Droplet: Transmitted through direct and indirect means. It can be inhaled directly by others when the infected patient cough or sneeze. In contrast, droplets may settle on table surface, and later on when another person touches the table before touching his own mucosal surfaces (including nose, mouth and eyes), the transmission of disease might then happen.

(2) Direct contact: Transmitted from the infected to the healthy through direct physical contacts.

(3) Indirect contact: Transmitted through fomites.

(4) Aerosols (possible): Aerosols are capable of traveling a longer distance and longer time in air, compared to typical droplets, before settling down owing to the small size and light weight. Aerosols can be generated during aerosol-generating procedures in hospital settings, such as resuscitation, endotracheal intubation, positive pressure ventilation, tracheostomy insertion, bronchosocopy, and airway suction, etc. Coughing, sneezing, toilet flushing, cigarette smoke and hot pot steam, etc. could also generate infective aerosols, further studies are needed to  test these hypothesis.

4.1c Survival time of SARS-CoV-2

• Viable SARS-CoV-2 could be detected in aerosol up to 3 hours after aerosolization, raising concerns on the possibility of viral transmission through aerosolization. 
• Viable SARS-CoV-2 could only be as long as 2-3 days on plastic and stainless steel. 

References

1. Cowling BJ, Ip DKM, Fang VJ, et al. (2013): Aerosol transmission is an important mode of influenza A virus spread. Nat Commun 4: 1935-1935.

2. Barker J & Jones MV (2005): The potential spread of infection caused by aerosol contamination of surfaces after flushing a domestic toilet. Journal of Applied Microbiology 99: 339-347.

3. Best EL, Sandoe JAT & Wilcox MH (2012): Potential for aerosolization of Clostridium difficile after flushing toilets: the role of toilet lids in reducing environmental contamination risk. Journal of Hospital Infection 80: 1-5.

4. Tran K, Cimon K, Severn M, Pessoa-Silva CL & Conly J (2012): Aerosol Generating Procedures and Risk of Transmission of Acute Respiratory Infections to Healthcare Workers: A Systematic Review. PLOS ONE 7: e35797.

5. Van Doremalen N, Bushmaker T, Morris DH, et al. (2020): Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. New England Journal of Medicine: In press.

4.2 Stopping The Adhesive Chain Together We Will Beat The Corona Virus

4.3 Microdroplet formation & prevention – A Japanese study

4.4 How Coronavirus Spreads Outdoors Vs. Indoors

4.5 Mutation Could Make Coronavirus More Infectious

4.6 How Exactly Do You Catch Covid-19? There Is a Growing Consensus

4.7 How Scientists Test Face Mask Effectiveness Against Coronavirus

4.8 How Effective Against Coronavirus Are Face Shields Compared To Masks?

4.9 Transplacental Transmission of SARS-CoV-2 Infection

4.10 Face Masks Really Do Matter. The Scientific Evidence Is Growing

4.11 You Probably Won’t Catch the Coronavirus From Frozen Food 

4.12 Scientists Warn It May Be Years Before Students Can Return to School Without Masks, Social Distancing

4.13 New Findings Warn of Higher Risk in Airborne Coronavirus Transmissions

4.14 Coronavirus in Vacant Apartment Implicates Toilet in Spread

4.15 It’s Easy to Point the Finger at Parties — But Younger Canadians Spread COVID-19 in All Kinds of Settings

4.16 Why We’ll Need Masks Even With a Coronavirus Vaccine

4.17 Would Herd Immunity Stop the Spread of Coronavirus?

4.18 How Dangerous is the Air Around Us?

4.19 How Long Does the Coronavirus Remain Viable on Surfaces?