Same thing happened with the Black Death. People escaped the cities to the countryside and spread the disease. They said the plague spread along by the trade routes. I noticed from the situation map in Wisconsin, the biggest concentration of CV cases right now seem to be along the I94 (Chicago-Milwaukee) and I90 (Chicago-Madison-La Cross) corridors.
Check out No.Dak.:
I-94 and US-2.
[Montana to follow]
Earlier in the month, you could look at the maps and make the case for I-80, US 30 and US 20 being the route of the spread in Iowa, but the epicenter in Johnson County (Iowa City, U of I, U of I Hospitals) might not be because of the roads, but rather a group of people coming back to IC from cruises and trips overseas and appearing asymptomatic in the poulation long enough to fire the prairie.