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Using cell phone data from one in 3 Americans, researchers have identified the indoor public places most responsible for the spread of Covid-19 in the spring, and they say that severely limiting occupancy of those places – mainly restaurants , gyms, cafes, hotels, and places of worship – could control the raging pandemic without resorting to lockdowns.
Their analysis also explains how disparities in risk contribute to the disproportionate burden of disease borne by people of color who have been less able than high-income whites to work remotely and who tend to visit grocery stores and other places. which tend to be smaller and more numerous. crowded than those in the white districts.
“This is in line with what we thought from the start, that there are certain activities that lead to spread more than other activities,” said Amesh Adalja, senior researcher at the Johns Hopkins Center for Health Security who did did not participate in the study. “When you think of targeted public health interventions, it’s important to focus on the activities where it’s happening and not be too blunt and block and stop all activities that haven’t necessarily been a problem. major factor of propagation.
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Using mobile phone data, scientists tracked the hourly movements of 98 million people from March 1 to May 2 to places they visited regularly, then mapped their movements to nearly 533,000 locations on propagation models. infectious diseases. The simulated transmission rates accurately predicted the number of actual daily cases in neighborhoods in 10 major metropolitan areas, including Chicago, New York and San Francisco. This allowed them to identify the “super-prevalent” sites that pose the greatest risk, the socio-economic factors that matter and what works to reduce the danger.
“Our results suggest that infectious disparities are not the inevitable consequence of factors that are difficult to treat in the short term, such as differences in pre-existing conditions,” Stanford’s Jure Leskovec and co-authors wrote in their paper published Tuesday in Nature. . “On the contrary, short-term policy decisions can dramatically affect the outcome of infection by altering the overall mobility allowed and the types of [places] reopened. “
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In Chicago, for example, 10% of places visited accounted for 85% of expected infections. Full-service restaurants, fitness centers, and places of worship had the highest overall risk of disease transmission, but this varied by neighborhood. In all 10 cities, snack bars and cafes were more frequented by residents of higher-income neighborhoods, but the risk of disease transmission was higher in those businesses located in lower-income neighborhoods.
Cell phone records do not reveal the race, ethnicity, or income of their users, but scientists found that their models were still able to predict higher infection rates among racial and socio-social groups. economic data based on census data. For example, a greater proportion of people who frequented restaurants in low-income neighborhoods than in high-income neighborhoods were infected. Residents of lower-income neighborhoods bought their food from smaller, more crowded grocery stores with 59% more people per square foot compared to markets in wealthier neighborhoods where more white people lived. They also visited grocery stores more often and spent 17% more time there.
The risk of infection with Covid-19 has increased with time spent in indoor public spaces. The study model predicts that setting an occupancy cap of 20% of maximum capacity for all these public spaces could reduce new infections by more than 80% while reducing the total number of visits by 42%. .
Analysis of what happened in the spring limits its applicability to the fall, said Adalja, who is also an infectious disease physician. Many other mitigation measures are currently in place in public places, from face blankets to temperature controls to occupancy limits. “If you went to a restaurant in early March, it’s a very different experience than going to a restaurant in early November.”
There are also limits to what mobility data can tell us now, he said.
“We have seen in epidemiology that now it is not restaurants or even large gatherings that promote the spread, but small gatherings,” he said, although the summer surge in the Sun Belt states was partly motivated by the people thronging the bars. As winter approached, the spread occurred more among people than in public places. This means that “people would not be captured by mobility data because they are at home, in their neighborhood.
Finding ways to help people stay at home could help erase the differences in how people move around based on their income. In the Chicago metropolitan area, the total number of visits to public places fell 54% in March, but in April, people living in low-income neighborhoods were 27% more likely to visit public places than residents of high-income neighborhoods. The authors said the gap likely reflects frontline workers in jobs that could not be performed remotely.
Beyond capping the occupancy rate in grocery stores, scientists are urging policymakers to open emergency food distribution centers. They also advocated for free and widely available testing in high-risk neighborhoods. To improve the lives of people who can’t work from home, they recommend a better paid vacation policy or income support so people can stay home when they are sick. For essential workers, they encourage better infection prevention in their workplace, including high-quality PPE, good ventilation, and separation where possible.
“These findings could play a valuable role in guiding political decisions on how to safely reopen society and minimize the damage caused by movement restrictions,” wrote Kevin Ma and Marc Lipsitch of Harvard TH Chan. School of Public Health in a commentary posted with the study. .
Cases and deaths are already increasing, before winter, when the virus can spread more easily in cold, dry weather that sends people indoors.
“I think this will be something where we have to get the whole population to take this very seriously, realizing that their behaviors have the most influence on the trajectory of these cases,” Adalja said.
In a teleconference with reporters, co-author Serina Yongchen Chang of Stanford said researchers observed raw trends in Chicago showing mobility is increasing, but as infection rates have increased in the summer, they did not reach previous pandemic levels starting in the spring. .
“The behaviors people adopt when on the move have a significant impact on transmission: better social distancing, going to different places in different ways,” she said. “It all has an impact.”
The next step for the researchers is to make an interactive tool available to local officials who seek trade-offs between health and economic consequences when considering reopening public places in their neighborhoods, Leskovec said on the call.
“Policymakers should be able to test different types of reopening depending on the impact of mobility on infections over time, as well as disparities in infections between demographic groups,” he said.
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