How the Virus Spreads and the Most Likely Infection Locations

Erin Bromage, a biology professor at the University of Massachusetts Dartmouth, has attempted to explain how infectious diseases spread in her article. She assessed the risk of coronavirus transmission in various situations, including weddings and birthday gatherings. The professor concluded that the likelihood of becoming a virus carrier outdoors is relatively low.

According to Armenpress, the professor aimed to answer many questions about where people become infected. Most people get infected right at home: a household member contracts the virus in the community, brings it home, where sustained contact with other household members leads to infection.

But where do people get infected in the community? The biologist noted that she often hears concerns about grocery stores, riding bikes, or runners not wearing protective masks... Are these places truly concerning? In the professor's opinion, not as much. She explained that it is necessary to be exposed to an infectious dose of the virus to get infected. Research on infectious doses for other coronaviruses indicates that only a small amount might be needed for infection. Some experts estimate that as few as 1,000 infectious viral particles of SARS-CoV2 might be sufficient. “Please keep in mind that this still needs to be experimentally determined, but we can use that number to illustrate how infection could happen. Infection could occur from 1,000 infectious viral particles received in a single breath or touching one’s eye once (rubbing) or from 100 viral particles that penetrate from each of 10 breaths. Each of these situations could lead to the spread of infection,” the professor remarked.

How long does the virus linger in the environment? Bathrooms have many surfaces to touch, such as doorknobs and faucets. Therefore, the risk of transmission in these environments could be higher. Caution should be exercised around public restrooms until more is known about the risk.

Coughing releases about 3,000 droplets, which can travel at speeds of up to 50 miles per hour. While many droplets are large and fall quickly, many remain airborne and can spread within seconds throughout a room. Sneezing releases approximately 30,000 droplets that can move at speeds of up to 200 miles per hour. Many droplets are small and spread over large areas (easily across the room). Thus, if a person is infected, a single cough or sneeze could release up to 200 million viral particles that can spread in their surrounding environment.

Exhalation releases 50-5,000 droplets. Most of these droplets fall quickly to the ground. Unlike sneezes and coughs that release a large number of viral particles, respiratory droplets released during normal breath contain lower viral levels. Speaking increases the release of respiratory droplets by about 10 times, producing 200 viral particles per minute. Assuming that each virus is inhaled, then a face-to-face conversation would require about 5 minutes to receive the necessary dose. Anyone spending 10 minutes in face-to-face conversation is potentially infectious. Thus, anyone sharing space with an infected person, for example in a workplace, for an extended period, is a potential carrier. This is why it is crucial for symptomatic individuals to stay home. The professor pointed out that sneezes and coughs expel so much virus that they can infect everyone in a room.

What is the role of asymptomatic individuals in virus transmission? The virus does not only spread through symptomatic individuals. At least 44 percent of infected people exhibit no symptoms. It’s possible to spread the virus in the environment up to 5 days before symptoms appear.

Then, Erin Bromage illustrated with an example how one infected person after going to work infected 94 of the 216 workers in the same floor within a week. Two of them were asymptomatic. However, the means of transmission remain unclear; it could have been the elevator button, doorknob, water cooler, etc. In the same building, but on different floors, three other individuals also became infected. Despite the interaction across floors in the building—like in the elevator or lobby—the outbreak was confined to just one floor.

The professor also shared a real story from Chicago about how an infected man, Bob, unknowingly spread the virus to his family members, attended a funeral where he hugged attendees and infected them too. These individuals exhibited symptoms, but Bob did not. Later, Bob attended a birthday celebration and infected 7 out of 9 guests. Subsequently, those who contracted the virus from Bob transmitted it to others in church. Thus, Bob was responsible for infecting 16 people, three of whom died.

The professor noted that the internal transmission within families, followed by community spread through funerals, birthday celebrations, and church gatherings, is considered responsible for the broader spread of Covid-19 in Chicago. Closed spaces, areas with inadequate ventilation, are seen as the primary risk zones for infection spread. Key sources of infection include homes, workplaces, public transport, gatherings, and restaurants. In contrast, retail stores do not constitute a primary risk area for transmission.