Detroit has a lot of international travel due to the auto industry. I believe dtw was one of the few airports in the country that was still accepting flights from china even after the travel ban in late January. That probably had a lot to do with the high community spread that occurred in the metro detroit area, which is where most of the cases and deaths have occurred. here is a good article that compared # of cases to ohio but applies to several other states as well https://www.mlive.com/public-interest/2020/04/6-reasons-michigan-has-four-times-more-coronavirus-cases-than-ohio.html