Superspreading events – when one or a few infected people cause a cascade of transmissions – may be especially important in driving the coronavirus pandemic in rural areas, researchers reported Thursday.
Their study of five counties in Georgia also showed shelter-in-place orders worked fast to bring cases down – usually within about two weeks. And younger people were more likely to spread the virus than people over age 60.
Biostatistician Max Lau of Emory University and colleagues analyzed state health department data in more than 9,500 coronavirus cases in four metro Atlanta area counties plus Dougherty County in rural southwestern Georgia between March and May.
“Overall, about 2% of cases were directly responsible for 20% of all infections,” they wrote in their report, published in the Proceedings of the National Academy of Sciences.
Health officials across the country have reported superspreading events related to birthday parties, funerals, conferences and other large gatherings.
People under 60 were almost three times as likely to spread the virus as people over 60, and tended to be responsible for superspreading, they said.
They also used location data from Facebook users to estimate how much people moved around and applied mathematical models to figure out how the reported cases fit in with behavior.
But the data is likely skewed, the Emory team said. Early on in the pandemic, especially, older people were more likely to be reported with infections because they were more likely to have serious symptoms.
“Due to the lack of widely available testing, the underreporting rate was almost surely high during earlier phases of the pandemic,” they added.