"COVID-19 FAQs" is a one-stop platform that helps you keep abreast of the latest developments in all fronts" said Editors-in-Chief, Dennis Lam & Jost Jonas

4. Transmission

Coronaviruses spread mainly through inhalation of droplets, direct or indirect contacts and to a limited scale, aerosol-related transmission. After being expelled, survival time of SARSCoV-2 varies among different materials (hours to days). To lower the risk of infection, we must always remain vigilant and be aware of personal hygiene!

Droplets & Aerosols



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. 


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 Sneezing and Coronavirus Disease 2019 (COVID-19)

4.5 The Latest in Coronavirus Science | The Daily Social Distancing Show

4.6 How Coronavirus Spreads Outdoors Vs. Indoors

4.7 Mutation Could Make Coronavirus More Infectious

4.7 Mutation could make coronavirus more infectious

4.8 Robin Daverman: A case of cold-chain food trade-disseminated contagion in Beijing

Robin Daverman (World traveler)

Now that there are 45 new local COVID-19 cases in Beijing, can someone explain whether this is going to affect the rest of the world?

This is actually significant. The reason is that this may be proven a clear case of cold-chain food trade-disseminated contagion.

Before the 1st case was discovered Beijing on June 10, Beijing had gone through 56 days without a single case. Totally clear. So when the contact tracers went through with the first patient, and published the patient’s 14-day-prior itinerary, the reaction was that “no way, how could he have gotten it if he never left Beijing?”

The next day, two more cases were discovered. Food inspectors. The common factor among all 3 cases was that they’ve all been to Xinfadi, which is the biggest grocery wholesaler/retailer in Beijing. Wholesale before 7 am in the morning. Retail after 7 am. Prices published online everyday, usually somewhat cheaper than everywhere else, because they sell stuff by the case.

So the local CDC swamped the place on June 12, collected ~ 2,000 people. 45 people tested positive, and the processing equipment for imported frozen salmon tested positive. The virus was isolated, sequenced, and ID’ed as the European variety. The top 3 salmon importers to China are Denmark, Norway, Chile.

Overnight, all Beijing grocery chains took imported salmon off the shelf. 9 neighborhood districts went into complete quarantine, local highways are cut off, and over 10,000 people are being tested and quarantined. All cold-chain food trade was suspended. All food distributors are temporarily closed for inspection and test. Of the six food wholesalers in Beijing, Xinfadi has 45 people tested positive, a second wholesaler had 1 person tested positive (who is also a close contact of one of the existing cases), the other 4 all tested negative.

You see, viruses can be killed at high temperature and preserved at low temperature. -20 degrees can perfectly preserve the virus for years. On normal surfaces, the virus can only survive for hours, or even days, but in cold freeze, you are talking years. In March, South Korea had a mysterious Covid-19 outbreak in their fishery department. In April Chile had a fishery outbreak. In May Ghana had a huge outbreak in their fish processing plant that accounted for over half of their total national count. A Fish-Factory Worker Infects 533 People With Covid-19 in Ghana The US just had its first major fishery outbreak. A Seattle fishing company has had more than 100 COVID-19 cases on its ships. They’re heading to Alaska this summer. – Alaska Public Media Additionally, the US has a massive number of meat processing plants workers and food inspectors died from Covid-19. Fourth USDA Inspector Dies Amid Meat Plant Virus Outbreaks

In the Wuhan outbreak in late Dec – early Jan, the very first batch of infected patients were also from the local food wholesaler, the Huanan Seafood Market. The material samples collected at the site showed positive samples on food processing equipment but not on any of the live animals there. So now people have to seriously consider if cold-chain storage and transportation maybe the source of both outbreaks. What if there was never any problem with the live animals, but the problem is with the frozen food.

What I think is going to happen is that food safety will become a big issue, and food processing plants, especially those using cold-process, will be required to certify that their plants and their workers are virus free before they can sell their products to China again. A lot of other Asian countries will follow suit, because they all, like China, managed to contain the virus domestically so they will be very much on guard to imported cases. Real-time health monitoring of food workers will almost certainly become the new normal in Beijing. In the meantime, consumers need to step up their food safety practice too, i.e., wash hands after touching cold-stored food, cook food thoroughly, sterilize their utensils and cutting boards after each use, etc.

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

4.9 How Exactly Do You Catch Covid-19.

4.10 China Suspends Imports from U.S. Meat Processor Tyson Foods

4.10 China Suspends Imports from U.S. Meat Processor Tyson Foods

4.11 How Scientists Test Face Mask Effectiveness Against Coronavirus

4.12 Hundreds of Scientists Say Coronavirus is Airborne, Ask Who to Revise Recommendations: NYT

Hundreds of scientists say coronavirus is airborne, ask WHO to revise recommendations NYT