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Where and how people are contracting the virus

Inspired by this article https://www.erinbromage.com/post/the-risks-know-them-avoid-them

Remember the formula:  

Successful Infection = Exposure to Virus x Time

Your sneezes and your coughs are dangerous 

A single cough  (3000 droplets – travels at 50mph ) or sneeze (30,000 droplets – travels at 200mph)  may contain as many as 200,000,000 (two hundred million) virus particles which can all be dispersed into the environment around them. They expel so much virus that you can infect a whole room of people. 

general breathing – single breath releases 50 – 5000 droplet or 20 viral particles minute into the environment, even if every virus ended up in your lungs (which is very unlikely), you would need 1000 viral particles divided by 20 per minute = 50 minutes.

Speaking increases the release of respiratory droplets about 10 fold; ~200 virus particles per minute. Again, assuming every virus is inhaled, it would take ~5 minutes of speaking face-to-face to receive the required dose

Anyone you spend greater than 10 minutes with in a face-to-face situation is potentially infected. Anyone who shares a space with you (say an office) for an extended period is potentially infected.  

Unlike sneezing and coughing which release huge amounts of viral material, the respiratory droplets released from breathing only contain low levels of virus.


Surfaces are areas of risk 

A Bathroom: Bathrooms have a lot of high touch surfaces, door handles, faucets, stall doors. So fomite transfer risk in this environment can be high

We know most people get infected in their own home. 

A household member contracts the virus in the community and brings it into the house where sustained contact between household members leads to infection.

Infection could occur, through 1000 infectious viral particles you receive in one breath or from one eye-rub, or 100 viral particles inhaled with each breath over 10 breaths, or 10 viral particles with 100 breaths. Each of these situations can lead to an infection.

So eho transmits and where does it transmit

You can be shedding the virus into the environment for up to 5 days before symptoms begin.

It’s the old 80-20 rule again…. data shows that just 20% of infected people are responsible for 99% of viral load that could potentially be released into the environment (ref)

Any environment that is enclosed, with poor air circulation and high density of people, spells trouble. 

biggest outbreaks are in prisons, religious ceremonies, and workplaces, such as meat packing facilities and call centers. 

super-spreading events are: 

  • Meat packing: In meat processing plants, densely packed workers must communicate to one another amidst the deafening drum of industrial machinery and a cold-room virus-preserving environment. There are now outbreaks in 115 facilities across 23 states, 5000+ workers infected, with 20 dead. 
  • Weddings, funerals, birthdays: 10% of early spreading events
  • Business networking: Face-to-face business networking 

Examples 

Workplaces: the outbreak in a call center (see below). A single infected employee came to work on the 11th floor of a building. That floor had 216 employees. Over the period of a week, 94 of those people became infected (43.5%: the blue chairs). 92 of those 94 people became sick (only 2 remained asymptomatic). 

A restaurant – people sitting for 1.5hrs – 50pc of table infected , 75pc of table next to them (based on airflow and ventilation) 

Choir – The choir sang for 2 1/2 hours, inside an enclosed rehearsal hall which was roughly the size of a volleyball court. A single asymptomatic carrier infected most of the people in attendance.

Indoor sports: 72 attendees at a Curling brought contestants and teammates in close contact in a cool indoor environment, with heavy breathing for an extended period. This tournament resulted in 24 of the 72 people becoming infected. (ref)

Birthday parties / funerals

Just to see how simple infection-chains can be, this is a real story from Chicago. The name is fake. Bob was infected but didn’t know. Bob shared a takeout meal, served from common serving dishes, with 2 family members. The dinner lasted 3 hours. The next day, Bob attended a funeral, hugging family members and others in attendance to express condolences. Within 4 days, both family members who shared the meal are sick. A third family member, who hugged Bob at the funeral became sick. But Bob wasn’t done. Bob attended a birthday party with 9 other people. They hugged and shared food at the 3 hour party. Seven of those people became ill. Over the next few days Bob became sick, he was hospitalized, ventilated, and died.

 

But Bob’s legacy lived on. Three of the people Bob infected at the birthday went to church, where they sang, passed the tithing dish etc. Members of that church became sick. In all, Bob was directly responsible for infecting 16 people between the ages of 5 and 86. Three of those 16 died. 

 

The spread of the virus within the household and back out into the community through funerals, birthdays, and church gatherings is believed to be responsible for the broader transmission of COVID-19 in Chicago. 

The main sources for infection are home, workplace, public transport, social gatherings, and restaurants. This accounts for 90% of all transmission events. In contrast, outbreaks spread from shopping appear to be responsible for a small percentage of traced infections. (Ref)

So….. enclosed space, sharing the same air for a prolonged period increases your chances of exposure and infection.  

commonality of outbreaks of COVID-19. 

All these infection events were indoors, with people closely-spaced, with lots of talking, singing, or yelling.

only a single outbreak has been reported from an outdoor environment (less than 0.3% of traced infections). 

The principle is viral exposure over an extended period of time. 

Even if they were 50 feet away (choir or call center), even a low dose of the virus in the air reaching them, over a sustained period, was enough to cause infection and in some cases, death. 

How to prevent contracting the virus 

Social distancing rules are really to protect you 

outdoor exposures is ok In these situations there is not enough time to achieve the infectious viral load when you are standing 6 feet apart or where wind and the infinite outdoor space for viral dilution reduces viral load. The effects of sunlight, heat, and humidity on viral survival, all serve to minimize the risk to everyone when outside.

If you are sitting in a well ventilated space, with few people, the risk is low. 

Outside is ok – would have to be in their airstream for 5+ minutes for a chance of infection.  

Clean surfaces. Those infected respiratory droplets land somewhere. Wash your hands often and stop touching your face!

Wear a mask to reduce what you release into the environment. It will help everyone, including your own business.  

This article Was inspired by Erin S. Bromage, Ph.D., is an Associate Professor of Biology at the University of Massachusetts Dartmouth


That was inspired by  a piece written by Jonathan Kay in Quillete

 COVID-19 Superspreader Events in 28 Countries: Critical Patterns and Lessons

Posted on May 14, 2020

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