Even with a long distance, prolonged time spent in a public indoor may expose you to COVID-19: Study

TORONTO – A new study suggests that physical distancing may not be the key to preventing the spread of COVID-19 indoors. Alternatively, the length of time you spend indoors, along with wearing the mask, may be a better indicator of the risk and the amount of chance that you will be inhaling airborne particles.

In a scenario presented by Interactive site Based on this new theoretical model, even if people are physically distant inside the church, if they weren’t wearing masks and singing, they could risk catching COVID-19 from someone else in the room within four to five minutes.

Research behind the model, Published Tuesday in PNAS MagazineLook closely at the six-foot rule – two meters in Canada – which has become the government’s standard recommendation on how to safely distance yourself from others while in public.

The researchers note that while the metran rule was originally developed when the transmission of COVID-19 was only thought to occur through heavy droplets falling from the mouth and nose during speech, coughing and sneezing, our understanding has since evolved.

Scientists are increasingly talking about the role of aerosols, which are smaller particles that stay in the air for longer, in the transmission of COVID-19.

The research stated that “the importance of the transmission of the Covid-19 virus through the air is now widely recognized.”

The researchers listed several examples indicating transmission through the air, such as an indoor choir practice of more than two hours in Washington state, where most choir members were infected with the virus although not all people were less than two meters away from an infected chorus. member. ; A two-hour bus trip to China during which 23 out of 68 passengers contracted the virus, regardless of seats; Such is the case with the virus that spreads through apartments in South Korea connected to the airways.

The fact that internal transmission is responsible for most cases of COVID-19 adds credence to the theory that the virus can remain in the air for longer periods.

It is important to distinguish between how the transmission of infection occurs, because while studies have shown that a distance of two meters is a sufficient distance between two people to stay safe from most of the droplets emitted from the patient’s mouth or nose, if infection through the air is the cause of the infection, as this is the case with some. Experts now believe this means that a person who follows physical distancing guidelines can get sick from airborne particles.

In this new study, researchers developed a theoretical aviation-based model in order to come up with new safety guidelines about how long it can be safely spent in a given space.

Airlift models are based on the notion that the pathogen is evenly distributed across a well-mixed interior space.

So, if an infected person is at home with others, such as a grocery store or restaurant, how much time would an uninfected person spend in that space before they risk contracting the virus?

The researchers report that the amount of time they can safely spend in an indoor space varies depending on a number of factors, such as face mask use, the size of the space, and the amount of ventilation.

The researchers also looked at how different respiratory activities, such as singing, speaking, and breathing, contribute to the total amount of exhaled particles and thus the potential amount of pathogens secreted. They found that singing was the most dangerous activity, allowing more particles to enter the air and diffuse faster, while breathing through the nose was less dangerous.

By balancing these factors, the researchers created a formula to judge how long a person might spend in a given indoor space that has at least one infected person before being exposed to the risk of contracting COVID-19.

“To reduce the risk of infection, long periods of time should be avoided in densely populated areas,” the research stated.

“One is safer in rooms with large size and high ventilation rates. Some are more at risk in rooms where people exercise in a way that increases their breathing rate and pathogen emissions, for example, through exercise, singing or shouting.”

Two graphs showed estimates of how long it would take for a person in a classroom or nursing home to be at risk of contracting the virus if in the air.

Assuming low transmissibility and average risk tolerance for children, the research estimated that with natural ventilation, masks, and social distancing, it would take about three days of steady time in a typical class of 20 children for someone to be at risk of contracting the virus. From an infected person. Classmate, regardless of whether social distancing is followed.

If all children were detected, a classroom of 20 kids with natural ventilation in the safe area would last for just over six hours, according to researchers’ estimates – and a classroom of 30 kids without masks and mechanical ventilation would be at risk. five hours.

Researchers have estimated that a nursing home with about three occupants and mechanical ventilation will become dangerous in just one day, provided they wear masks. The study suggested that without the masks, it would take only 30 minutes to be in a typical nursing room with an infected person before one of the other passengers was at risk of contracting the virus.

Obviously, a six-foot base […] It becomes insufficient after a critical period. “

New safety manual?

The average person clearly does not know the exact dimensions and ventilation of each building they enter to relate them to the formula.

But researchers Site released Along with their research that helps simulate some common indoor sites.

The website allows people to define an average room such as a classroom or a restaurant, as well as how many people are in that room and what they do (rest, sing, wear masks, or not wear masks) and calculate the average time that it would be safe to pass to that room if it were There is a virus present in the air.

For example, according to the app, in an average classroom singing to adults without masks, 10 people would be safe for only five minutes.

Safety guidelines will be violated within three minutes if there are 25 people in the room.

The site estimates that five people over the age of 64 who were talking to each other without face masks in the living room would be at risk of contracting the virus from an infected person in the room in just 47 minutes.

The app also lets viewers dedicate a room to assess building safety and more specific situations.

The researchers realized that their model included estimates of virus transmission and a hypothesis that the pathogen would mix evenly in a room, which may not be true in an indoor environment with less ventilation.

The research said: “We confirm that our guidelines have been developed specifically with the aim of mitigating the risks of long-range airborne transmission.” Note, however, that our conclusions [of infectiousness of exhaled air] It resulted from a series of common super-events that may also have contributed to other modes of transmission, such as breathing planes. Hence, our appreciation for [the infectiousness of exhaled air] These are necessarily exaggerated estimates and should be higher than those that would have resulted from long-distance air transport. “

The researchers said the safety guidelines for the transmission of air “provide a conservative upper”. [cumulative exposure time]. “

This new research doesn’t mean it’s pointless to distance yourself from others in the home. Coughing or sneezing directly from someone with COVID-19 is dangerous no matter what time you spend in the room.

But when assessing the internal hazards other people might infect, it appears that the most important measures to keep you safe may be a face mask and a shorter flight rather than a two-meter bubble.