Once again, a study on COVID-19 spread is making headlines. The latest one focuses on which locations are driving the greatest spread of the virus.
According to the study, full-service restaurants, gyms, hotels and religious organizations are responsible for most COVID-19 spread. At least that's what it appears to say when you look at headlines and social media.
As always, there's more context you should know when reading about the study.
THE QUESTION
Did a study find that full-service restaurants, gyms, hotels and religious organizations are responsible for the majority of COVID-19 spread in the United States?
THE ANSWER
Yes, but only among the group of places the study analyzed and only in urban areas. There are some gaps in the study that require more research to fill in.
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WHAT WE FOUND
Like most other new studies about COVID-19 you see, this study is in pre-print and has yet to finish the peer review process. That means other scholars in the field have yet to look it over to ensure it has sufficient scientific rigor. The journal the study was published in, Nature, allows you to see some of the comments in the peer review file.
The study's text can be found by clicking the "download PDF" button on the right side of the Nature page. There you can read the study in full.
The researchers used anonymous cell phone location data to track the hourly movements of 98 million people in 10 of the largest American metro areas in March and April: New York City, Chicago, Los Angeles, Houston, Dallas, Philadelphia, Atlanta, San Francisco, Miami and Washington, D.C.
They used this data to analyze COVID-19 transmission rates at religious organizations, physicians' offices and a number of various commercial and retail locations ranging from restaurants to hotels to secondhand shops. They also created a model to simulate multiple outcomes.
A few conclusions stand out from their research: a small number of places are responsible for the majority of transmission; density matters and; not every neighborhood experiences the same transmission risks at the same locations.
Those places where transmission was the highest were full-service restaurants, gyms, cafes, hotels, limited-service restaurants and religious organizations. But this is where those last two conclusions come into play.
While grocery stores were found not to carry as much risk for transmission compared to those above places in the general population, there were higher transmission rates in lower-income neighborhoods. That's because the grocery stores in those neighborhoods were denser with more people per square foot and the people in those stores stayed inside longer. One of the researchers said in a separate article on Nature about the study that there are fewer grocery stores in those neighborhoods, so people have fewer options to spread out the density.
This idea that a location has higher COVID-19 transmission rates if it's denser is reflected in the simulation model created by the researchers as well as some of their policy hypotheses. "Compared to full reopening, capping at 20% maximum occupancy in Chicago cuts down new infections by more than 80%, while only losing 42% of overall visits," the research paper reads.
Their hope is that this work can help inform public policy. Knowing which places are hot spots and having models for just how much various restrictions affect both virus spread and business loss can potentially guide policy on reopenings, lockdowns and restrictions.
But the study doesn't capture the full-picture as of yet.
For one, there are several places of interest where COVID-19 transmission was not studied. Schools, prisons, nursing homes, hospitals, and transit stations were all excluded. So it doesn't show how transmission in restaurants and hotels compare to those places.
It also focused solely on large urban areas. The research showed how access to options and density affect the rate of spread in different places and the density in restaurants, grocery stores, and churches may differ in small towns than in big cities. So there would need to be research focusing on more rural areas to know if the findings are consistent in those places.
Additionally, the research was led by the Department of Computer Science at Stanford University. So while the researchers have an extensive background on data and modelling, which their study focused on, they don't have as deep of a background on viruses as an epidemiologist would.
None of that means the research is untrustworthy. It just means that more studies are necessary to get the full picture. The article in Nature used the input of an epidemiologist to highlight that.
"But Christopher Dye, an epidemiologist at the University of Oxford, says these mobility patterns need to be validated with real-world data. 'It is an epidemiological hypothesis that remains to be tested. But it is a hypothesis that is well worth testing,' he says."
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