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
In addition to the very worst outbreaks, which have been in nursing homes, the biggest outbreaks of coronavirus infection so far around the world have been associated with prisons, religious ceremonies, and workplaces.
In an article published by the World Economic Forum (WEF), Associate Prof of Biology Erin Bromage at University of Massachusetts, Dartmouth, outlined how any environment that is enclosed, with poor air circulation and high density of people, spells trouble.
In a study titled, “COVID-19 Outbreak Associated with Air Conditioning in Restaurant, Guangzhou, China, 2020" published by Emerging Infectious Diseases (EID) Journal of CDC, scientists studied the airflow in restaurants in connection with the spread of coronavirus.
The study involved 3 family clusters. The airflow direction was consistent with droplet transmission.
In one case, an infected person sat at a dinner table with nine friends. Dinner took about 1 to 1.5 hours. During the meal, the asymptomatic carrier released low-levels of virus into the air from their breathing.
Approximately half of the people at the infected person's table fell ill over the next week. And, approximately half of the people from surrounding tables also caught the infection.
To prevent the spread of the virus in restaurants, the scientists recommend increasing the distance between tables and improving ventilation.
Another good example of the coronavirus outbreak was in a call centre, recorded in a study titled, “Coronavirus Disease Outbreak in Call Center, South Korea” published in EID Journal.
A single infected employee came to work on the 11th floor. That floor had 216 employees. Over the period of a week, 94 people became infected. Of whom, 92 fell ill while only 2 remained asymptomatic.
Only one side of the office -- where the infected person sat -- got primarily infected, while very few people got infected on the other side.
Another 3 people on other floors of the building were infected, but the authors were not able to trace the infection to the primary cluster on the 11th floor.
Interestingly, even though there was considerable interaction between workers on different floors of the building in elevators and the lobby, the outbreak was mostly limited to a single floor.
In short, being in an enclosed space and sharing the same air for a prolonged period may increase your chances of exposure and infection.
This is also a real story from Chicago. Bob (name changed) was infected but unaware. Bob had shared a takeout meal, served from common serving dishes, with two family members. The dinner lasted three hours. The next day, Bob attended a funeral, hugging family members and others in attendance to express condolences.
Within four days, both family members who shared the meal fell sick. A third family member, who hugged Bob at the funeral also got ill.
However, Bob wasn't done. He attended a birthday party with nine others. They hugged and shared food at the 3-hour party. Seven people present became ill.
But Bob’s transmission chain wasn’t complete. Three of the people Bob infected at the birthday went to church, where they sang and passed the tithing dish. Members of that church became sick. All 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.
Commonality of outbreaks
The reason to highlight these different outbreaks is to show the commonality of outbreaks of Covid-19. All these infection events were indoors, with people closely-spaced, with lots of talking, singing, or yelling.
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.
Importantly, of the countries performing contact tracing properly, only a single outbreak has been reported from an outdoor environment (less than 0.3% of traced infections).
If you are sitting in a well ventilated space, with few people, the risk is low.