by Tony Wikrent
The Risks – Know Them – Avoid Them
[ErinBromage, via Mike Norman Economics 5-8-20]
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.
But where are people contracting the infection in the community? I regularly hear people worrying about grocery stores, bike rides, inconsiderate runners who are not wearing masks…. are these places of concern? Well, not really. Let me explain….
Remember the formulae: Successful Infection = Exposure to Virus x Time
….Ignoring the terrible outbreaks in nursing homes, we find that the biggest outbreaks are in prisons, religious ceremonies, and workplaces, such a meat packing facilities and call centers. Any environment that is enclosed, with poor air circulation and high density of people, spells trouble.
Some of the biggest 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. (ref)
- Weddings, funerals, birthdays: 10% of early spreading events
- Business networking: Face-to-face business networking like the Biogen Conference in Boston in March.
As we move back to work, or go to a restaurant, let’s look at what can happen in those environments.
Restaurants: Some really great shoe-leather epidemiology demonstrated clearly the effect of a single asymptomatic carrier in a restaurant environment (see below). The infected person (A1) sat at a table and had dinner with 9 friends. Dinner took about 1 to 1.5 hours. During this meal, the asymptomatic carrier released low-levels of virus into the air from their breathing. Airflow (from the restaurant’s various airflow vents) was from right to left. Approximately 50% of the people at the infected person’s table became sick over the next 7 days. 75% of the people on the adjacent downwind table became infected. And even 2 of the 7 people on the upwind table were infected (believed to happen by turbulent airflow). No one at tables E or F became infected, they were out of the main airflow from the air conditioner on the right to the exhaust fan on the left of the room. (Ref)
Workplaces: Another great example is 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 become infected (43.5%: the blue chairs). 92 of those 94 people became sick (only 2 remained asymptomatic). Notice how one side of the office is primarily infected, while there are very few people infected on the other side.



