At least 23 cases have been traced to outbreaks occurring at rally events in Bemidji on September 18, a speech held by Vice President Mike Pence on September 24 in Minneapolis, and another rally held by President Donald Trump on September 30 in Duluth, the department said in an email to CNN.
In the month preceding the rally, the seven-day average of new cases in Beltrami County, where Bemidji is located, was 2.85 new cases a day, according to Johns Hopkins University.
In the month before the event, the seven-day average was just under 180 new cases in Hennepin County and had dropped to an average of 169 new cases on the day of the vice president's visit, according to Johns Hopkins.
Another four cases have been traced by the Minnesota Department of Health to a rally the President held on September 30 in Duluth.
But that might not be enough time—with delays emerging across the country and in competitive voting states, according to a Wall Street Journal analysis of data showing average first-class letter delivery times provided by mail-tracking firm GrayHair Software.
Of the 29 states that require mail-in ballots to arrive on or before election day, 28 have since late July seen periods of average delivery times exceeding six days, the Journal analysis found.
Mail slowdowns hit several of those states in the week ending Oct. 17, the GrayHair data show.
The latest figures from the Postal Service, which lag the GrayHair data, show a slight slowdown in the week ending Oct. 10, with about 85.6% of first-class mail delivered on time.
More 3.1 billion mail pieces were processed that week, up about 23% from the average volume in September, the Postal Service said.