Capping the number of diners in restaurants and cafes at 20 per cent of normal occupancy would cut the number of coronavirus infections and be a promising route out of lockdown, new research has shown.
The research, published in the journal Nature, found that putting a limit on occupancy in cafes, restaurants, gyms and hotels would reduce the number of infections by 80 per cent but would only reduce the number of overall visitors by 40 per cent. They said that restaurants posed the greatest infection risk.
Researchers combined mobile phone data – collected between March 1 and May 1 – and modelling information to track the movements of millions of people in the 10 biggest cities in the United States.
The level of detail of the mobility data allowed the researchers to model the number of infections occurring at nearly 553,000 distinct locations grouped into 20 categories — termed “points of interest” — that people tended to visit regularly.
The data captured the movements of people from local neighbourhoods of between 600 and 3,000 people to look at where people were going from hour to hour and predict where infections were most likely to happen. The model assumed a low level of infection in every neighbourhood.
The model showed that a small number of locations accounted for a large majority of infections. For example, in Chicago 10 per cent of these points of interest were responsible for 85 per cent of infections.
Jure Leskovec, associate professor of computer science at Stanford University and co-author of the paper, said these places tended to be smaller, more crowded and where people lingered. The study found that restaurants posed the greatest risk for infection spread and calculated that if they reopened fully there would be an additional 596,000 infections in Chicago alone by the end of May.
Dr Leskovec added: “There is an important trade off between wanting to restart the economy but also wanting to minimise the number of Covid cases. Our work highlights that it doesn’t have to be all or nothing… Our model provides a tool for policy makers to navigate these trade offs and make the right decisions,” he said.
The paper also highlighted disparities in movements and infection rates between different socio-economic groups. People on lower incomes did not reduce their movements as much as those on higher incomes between March and May – possibly because they were less likely to be able to work from home.
Grocery stores in lower income districts had on average 59 per cent more people per square foot than those in richer areas, and shoppers stayed 17 per cent longer on average – putting them at greater risk of infection. The research showed that someone on a lower income is twice as likely to pick up Covid at a supermarket than someone on a higher income, living in a more expensive area.
The researchers said the study would enable authorities to target interventions such as providing free testing to areas that were deemed to be high risk or providing emergency food distribution centres to reduce the number of people visiting grocery stores.
Serina Chang, research student and co-author of the paper, said that the modelling also showed that people in more ethnically diverse neighbourhoods were at greater risk of infection.
“These disparities and Covid infection rates are well reported but this suggests that mobility may be a strong contributing factor. Our model is able to analyse how mobility relates to disparities and to estimate different reopening plans may exacerbate or reduce inequalities,” she said.
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