On Apr. 2, 2020, a University of Chicago team announced that it had mapped confirmed COVID-19 infections per county – and adjusted for population sizes.

The researchers’ findings revealed significant clusters in parts of Georgia, Arkansas and Mississippi, among other areas. Even though the involved populations may be smaller than those of New York or Seattle, they could be disproportionately hit by the disease.

“When you flip from just state-level data to county-level data, you get a lot more information,” says Marynia Kolak, assistant director of health informatics at the University of Chicago’s Center for Spatial Data Science, who co-led the team that created the maps. “For example, there are a lot of areas

The mapping team initially used data from a crowd-sourced tracker of county-level cases and validated them with estimates from state health departments. The researchers have since incorporated data from several other sources, and they are partnering with their colleagues at the University of Wisconsin–Madison to authenticate that information.

The University of Chicago group compiled data on both state and county levels, looking at each area’s confirmed cases, deaths and number of cases weighted by population size. The team also created an interactive visualization that shows the evolution of regional hotspots over time.in the South where the population is a lot smaller, but the proportion of people who have [COVID-19] is a lot greater. So that can cause potential challenges, because even though there are less people who have the virus, there are also correspondingly fewer hospital beds, [intensive care units] or ventilators.”

The data reveal some surprising patterns in infection rates at the county level after adjusting for population size. For example, many county clusters—such as those around Albany, Ga., Detroit, Nashville, Tenn., and parts of Mississippi and Arkansas—had relatively large numbers of cases per capita. As of March 29, the county cluster encompassing New York State, New Jersey and Massachusetts still had the most confirmed infections both overall and per capita: 76,273 cases, or about 22 per 10,000 people. Yet Albany, Ga., had the second-highest number per capita: 13 cases per 10,000 people. That figure was much higher than those of other well-known hotspots, such as Seattle, which had about eight cases per 10,000, and San Francisco, which had two per 100,000.

The new findings could have critical implications for controlling the spread of the virus. One of the main take-home messages, Kolak says, is the importance of policies on social distancing and isolating each outbreak before it gets more serious. “Rather than wait for it to get so extreme that, you know, the whole state emerges as a hotspot,” she says, “try to contain it within a county before it goes further.”