GREEN BAY - Investigators from the Centers for Disease Control and Prevention are expected to arrive in Brown County this weekend to look into a recent explosion in COVID-19 cases in the Green Bay area.

The number of cases has increased more than fourfold in just 10 days.

The Wisconsin Department of Emergency Management will join the CDC in sending people to Brown County to help identify the source or sources of recent coronavirus cases, county officials said.

Other northeastern Wisconsin county health departments may also participate.

County officials requested help after becoming worried earlier this week about the magnitude of the spread of the virus. Besides the speed at which it was spreading, they fear the virus is being transported to nearby counties by people who come into Brown County to work or conduct business, then return home.

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"Our biggest concern is the rate of new cases," said Ted Shove, the county's environmental health manager. "A couple days ago, we were on the far left side of the curve. … Our concern for requesting and bringing in additional resources is we really want to slow the spread."

Brown County's increase in confirmed cases is the most pronounced in the state since the spring election. The state Department of Health Services reported the county had seen 41 positive tests by April 7. By April 17, that number had more than quadrupled, to 180.

That's a 340% increase. In that period, statewide totals increased by 57%.

The county's concerns about the increase, Shove said, include the role "a non-governmental organization with multiple locations countywide" might be playing in the spread of the virus. He said the county suspects a connection between "a cluster of cases" and a location where "operations are not accessible to the public."

Shove would not identify the organization, or divulge any specific locations that concern health officials.

He said, though, that the county does not believe the elections earlier this month are responsible for the increases in cases in Brown County, at least so far.

Twenty-nine of the new Brown County cases reported by the state on Friday were in an area east of the East River and south of Main Street in Green Bay.

Most people who develop COVID-19 symptoms do so within 12 days of becoming infected. The election, which involved a reduction in polling places in Green Bay from 31 locations to two, and long lines outside the polls, happened April 7.

County health officials initially shared little information Friday during a 3 p.m. conference call with reporters. Shove read a brief statement, then left the call. He and Health Officer Anna Destree spoke with the Green Bay Press-Gazette later in the day.

Destree said county residents don't need to take extra precautions in the wake of the latest news, but said people should take the advice to stay home and avoid close contact with other people seriously, not just when it seems convenient.

Statewide, of 28 Wisconsin counties that had more than five cases on April 7, only two others saw cases double: Walworth County, which went from 21 to 75 cases (257%), and Racine County, which went from 66 cases to 157 (138%).

The city of Milwaukee had similarly long lines on election day after its 180 polling stations were reduced to just five. But Milwaukee County's 52% increase in confirmed cases over the same period was below the state's average.

Milwaukee County has a recent spike in positive cases, but this corresponds to a similar increase in testing (the percent of all tests coming back positive has remained flat). In Brown County, the spike in positive cases has occurred even as testing has remained relatively flat.

Research on the early cases in China shows the average incubation of the coronavirus was five days. Brown County's case total began to climb in earnest the day of the election, suggesting that polling sites wouldn't have been the initial source of the spread.

Andrew Mollica of the Journal Sentinel contributed to this report.

Contact Doug Schneider at (920) 431-8333, or DSchneid@gannett.com. Follow him on Twitter at @PGDougSchneider