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Interiors in which many people spend long periods of time have long been considered perfect for the spread of the coronavirus and a frequent location for so-called super-spread events. A great analysis of US data confirms this impression once again.
According to this, a large part of infections occurs only in a few places, which are characterized by the fact that people stay there for a long time in larger groups. The reopening of restaurants, cafes and gyms are therefore the main drivers of the number of infections.
The results are based on analysis of anonymous cell phone movement data for 98 million Americans in ten of the nation’s largest metropolitan areas, including New York, Los Angeles and Chicago. They were published in advance in the specialized journal “Nature” without a specialized review and all data and calculation models were made available.
80 percent of infections can be attributed to ten percent of locations.
Scientists led by David Grusky of Stanford University in California fed a computer model with the data and recorded which places people visited between March and May 2020, how long they stayed there, and how many people they met. They compared that to the number of corona cases reported per day.
In this way, the model learned to predict the probability of infection in different cities using mobility data. “We can simulate where and when people get infected,” said PhD student Serina Chang, who participated in the work.
Half a million different locations were considered, including parks, churches, restaurants, stores, gyms, pet stores, and car dealerships. “Up to 80 percent of the infections were due to only 10 percent of the locations,” Chang said. However, the results varied somewhat from city to city.
Lower density of people, great protection.
However, one principle always remained the same: “We have found that a reduction in the number of people in a place significantly reduces the risk of infection,” Grusky said. Researchers also see this as an opportunity.
For example, restaurants and cafes could possibly stay open for the long term if the number of visitors were more limited. This could also prevent infection in supermarkets.
If the researchers limited the occupancy of public spaces in the Chicago metropolitan area in their model to 20 percent, the expected number of new infections has already dropped by more than 80 percent. With movement limits at restaurants playing a role, especially during peak hours, restaurants only lost 42 percent of their guests despite this tough measure, the Bloomberg news agency reports.
What measure contributes how much?
In an accompanying article, Kevin Ma and Marc Lipsitch of Harvard’s TH Chan School of Public Health note that the model could also help clarify the question of which measures have what impact on the number of infections. So far it cannot be said in detail.
By simulating hotel infections in Miami, the model showed, for example, that these peaked when wild spring break parties were reported in March despite the corona pandemic. After the entry into force of the closure measures, the number of infections in the model and actually fell again.
According to the Bloomberg report, health expert Eric Topol of the Scripps Research Translational Institute suggests compiling the detailed data on a national virus panel. On this basis, politicians could take more specific countermeasures.
There is no such simulation program for Germany. However, the information could also help in this country to make more specific decisions on opening measures after the current closure to reduce the social and economic damage caused by the pandemic.
