Science

# Interactive tool calculates the risk of catching Covid-19 if one person is infected

A complex mathematical equation to work out the risk of catching the coronavirus if one person in a room is infected Covid-19 has been turned into a handy online tool.

Created by researchers at MIT, it assumes a room hosts one infected person and allows the user to customise the settings of the room and the behaviour of its inhabitants.

For example, the tool allows people to change the size of the room; what, if any, ventilation is present; what masks are being worn; how strict are people being in their mask wearing; and how loud and gregarious people are being.

It allows users to mock up the risk of mingling over the festive season in their dining room, lounge or kitchen.

Ventilation and the wearing of high-quality face masks was found to be the most crucial changes people could make to extend the safe limit.

You can try the interactive tool out for yourself here.

An interactive tool allows people to calculate the risk of catching Covid19 if someone in the room tests positive. Ventilation and masks were found to be key. If a meal can not be eaten outside, like in the winter months surrounding Christmas, opening a window can help reduce the risk, as cna wearing high-quality surgical masks and not cotton coverings (stock)

In a standard room with 8ft tall ceilings and each wall measuring around 15ft long, ten fit young people all diligently wearing surgical face masks could safely sit there talking normally for two hours if the windows were shut due to the cold temperatures outside.

But, for a family of ten, of which some are elderly, in a standard dining room for Christmas dinner where nobody is wearing a mask because they are eating and the windows are closed because it is cold outside — and there’s a few heated discussions with raised voices — the tool reveals the safe limit is slashed to just three minutes.

Its developers say the online site allows people to calculate risk with more nuance than the simple, and often vague, guidance to form ‘bubbles’ or socially distance.

Calculations which inform the site were published by authors John Bush and Martin Bazant on the pe-print server medRxiv

In a standard room with 8ft tall ceilings and each wall measuring around 15ft long, ten fit young people all diligently wearing surgical face masks could safely sit there talking normally for two hours if the windows were shut due to the cold temperatures outside, according to the tool, based on calculations from MIT researchers (stock)

It is based on fluid dynamics and bases its safe figure on cumulative exposure time and airborne transmission only. It is also only able to account for one infectious person in a group.

### How coronavirus infects the BRAIN

The coronavirus can reach the human brain after being inhaled through a person’s nose and getting stuck in their nasal mucus, a study has found.

It is the first known proof the coronavirus can infect the brain’s neurons via the mucosal pathway.

Throughout the course of the pandemic, it has become clear the coronavirus, called SARS-CoV-2, does not just cause respiratory distress but neurological issues as well.

For example, one in three report symptoms such as loss of smell or taste, headaches, fatigue, dizziness, and nausea.

Scientists in Germany performed autopsies on 33 patients who died of Covid-19 and studied the mucus at the back of the nose — above the mouth where the throat joins the nasal cavity — as well as samples of brain tissue.

Genetic material of the coronavirus was present in largest quantities in the mucus of the nasal cavity, but SARS-CoV-2’s spike proteins — which protrude from the virus and latch onto human receptors to infect the cells — were also found in the brain.

Dr Frank Heppner, co-author of the study from Charité–Universitätsmedizin Berlin, says: ‘Once inside the olfactory mucosa, the virus appears to use neuroanatomical connections, such as the olfactory nerve, in order to reach the brain.’

This makes it useful for small gatherings, but in larger places where there may be dozens of people, for example at a supermarket, the application becomes unusable.

However, people can visualise the impact of what their household Covid protocols can do. For example, in a living room of 400 square feet, if five young people all wear a N95 respirator they can dance and sing safely for 35 minutes.

But dropping the mask to below their chin just 50 per cent of the time sees this figure drop to four minutes.

While parameters of the room and mitigating aspects are important, the researchers say, the most critical impactor is human behaviour. Specifically, the wearing of high-quality face masks.

In their study, the researchers applied their work to two case studies which have both garnered huge scrutiny over their role in spreading the disease: classrooms and care homes.

For a typical US classroom with 19 students and one teacher, the researchers found that without masks ‘the expected time for the first transmission after an infected individual enters the classroom is 2.3 hours for natural ventilation and 18 hours with mechanical ventilation’.

‘With enhanced ventilation and judicious mask use, this time limit could be extended to several weeks, and so exceed the recovery time for Covid-19,’ they add.

Extended periods of physical activity, several people talking at the same time, or singing would lower the time limit by an order of magnitude, the researchers caution.

However, the good news for classrooms is not replicated for care home,s they ay, cautioning their analysis ‘sounds the alarm’ for long-term care facilities.

They say that three elderly people each with 80 square feet of space in a room with open windows are only safe for three minutes if the rule of 2m (6ft) social distancing is followed.

The maximum safe limit for occupying this space if one person is infected is just 17 minutes, according to the model.

‘This example provides insight into the devastating toll of the Covid-19 pandemic on the elderly,’ the researchers say.

‘Furthermore, it underscores the need to minimize the sharing of indoor space, maintain adequate, once-through ventilation, and encourage the use of face masks.’