GREEN BAY - It was mid-March and Brown County had recorded its first coronavirus case just days earlier. Local health officials declared themselves ready to battle the pandemic.

They introduced a phrase few people had heard: "social distancing." Medical professionals spoke as if they were gearing up for war — one they planned to win.

"We're not ever going to stop fighting," Prevea Health CEO Dr. Ashok Rai proclaimed. "There is no crying uncle in this."

A month later, the war took a turn for the worse. Brown County's spike in cases was subtle at first, until it became unmistakable.

Federal investigators are now looking into clusters of cases, as county officials try to control an outbreak that seemed to catch them off guard.

Here's how Brown County became Wisconsin's hottest hot zone in the COVID-19 pandemic.

An Easter surprise no one wanted

The weekend after St. Patrick's Day, just two of Brown County's 260,000 residents had the virus. And preventive measures had been stepped up: Green Bay Mayor Eric Genrich closed City Hall to the public to help slow the virus' spread. Gov. Tony Evers, who had ordered that Wisconsin residents avoid gatherings of 50 or more people, reduced that number to 10. Schools closed across the state.

The county medical community and its residents seemed ahead of the game. Case numbers were increasing more slowly than in other parts of the nation; Brown County had fewer coronavirus patients than Fond du Lac County, which has 160,000 fewer residents.

As Easter approached, those measures still appeared to be working.

"We were at about 50 cases and things looked manageable," County Executive Troy Streckenbach said Thursday. "People were following orders (to avoid contact with others), and things seemed very optimistic. The big numbers we were seeing in urban areas like Milwaukee and Madison were things we didn't think we'd see up here."

Just days later, optimism turned to urgency. The scene changed dramatically.

» Brown County's cases of COVID-19, the disease caused by the coronavirus, began to explode around April 13. In a week, cases increased by 1,000% to surpass 500. With 618 confirmed cases as of Friday, the state's fourth most-populous county now trails only Milwaukee County in Wisconsin. Brown County has the highest rate of tests coming back positive, at 26%.

» Employee safety in Green Bay's meatpacking industry is under a microscope, after public health officials connected over half the county's cases to two beef-processing companies and a sausage-maker. Officials on Friday had linked 189 COVID-19 cases to JBS Packerland on Lime Kiln Road. Another 75 were tied to an American Foods Group operation in Green Bay. Denmark sausage manufacturer Salm Partners has been linked to 23.

» An investigation that barely a week ago was the sole province of Brown County Public Health has expanded to include experts from federal and state agencies. That includes four scientists from the U.S. Centers for Disease Control and Prevention who arrived Monday after county health officials realized they needed outside help. It includes the Occupational Safety and Health Administration, which acknowledged Friday it is investigating JBS and American Foods plants in Green Bay.

The county's daily conference calls with journalists now attract reporters from CNN, the Associated Press and the CBS Evening News.

'We need it to look like a ghost town'

For weeks, while the nation focused on virus hot spots in the Seattle area, New Orleans and New York City, Brown County's case numbers stayed flat. Even as outbreaks in the Milwaukee area drove Wisconsin's total over 100, the Green Bay area seemed largely unaffected.

Inside a basement anteroom of the county's central library on March 18, though, a health official sounded a quiet warning.

Health and Human Services Director Erik Pritzl, after discussing the county's second coronavirus case, asked a Green Bay Press-Gazette reporter about the number of people outside and the volume of traffic on the roads earlier that evening.

The reporter said the scene looked like downtown Green Bay during a Packers game — virtually deserted.

"They're nowhere near deserted enough," Pritzl replied. "To beat this thing, we need it to look like a ghost town."

Brown County starts outpacing the state

On March 25, Wisconsin's case total shot past 500. Brown County had three.

Many county residents had heard that the virus could last a while on metal surfaces. But if we were only going to be in a grocery store's self-check aisle for a minute or two, that seemed safe.

On March 29, Wisconsin topped 1,000 cases. Brown County was at six.

In an emergency room at Bellin Hospital, Dr. Paul Casey was treating the first of his COVID-19 patients. He had spent the past three weeks creating in-patient guidelines to prepare for an onslaught of the infected.

"We'd been preparing for an influx … and we ended up waiting and waiting," he said.

Casey's initial patients had little in common besides an infection and a Brown County address. The first had become infected on a cruise. The second via European travel. The third likely because a family member brought the virus home from out of the area.

On April 4, Wisconsin's total exceeded 2,000, doubling in six days. Brown County's numbers grew at over twice that rate, but still totaled just 27 cases.

Six days later, Wisconsin's total topped 3,000. Brown County's continued to grow twice as fast as the rest of the state, but didn't yet cause alarm, even as it reached 55.

Potential cause identified

Sometime in early April, Casey and others agree, something significantly changed the landscape in Brown County.

It might have been the unusually warm weather — two days of temperatures in the low 60s, four in the high 50s — proving irresistible to families cooped up for weeks without a spring break trip or even a day at school. Or Easter's promise of rebirth, which might have borne extra significance amid the pandemic.

Health officials had continued to recite standard guidance for the past month: Stay home. Cover your nose and mouth. Avoid other people. But the county didn't turn up the volume until last week, even while acknowledging their message likely was beginning to lose its influence as people grew impatient.

"We're social people. We like to be at other people's houses, to be outside," Pritzl, the county health director, said Friday. "When it's taken away, it's really difficult. Even if it's just, 'I really want to see the people in my family that I haven't seen.'"

Casey, the ER doctor, suspects other problems: Some meatpacking workers primarily speak Spanish, and might not understand a health warning in English. Other people refused to listen.

"Not everybody hears the right message, because it's been politicized," he said. "So it depends on the type of media you read or listen to. Some of the people who need to hear this are only listening to (politically charged) media."

Something a public health official says to promote safety via social-distancing is construed by some as government's attempt to limit civil rights or weaken the economy. That can help fuel a protest like Friday's demonstration in Madison opposing Evers' "Safer at Home" order.

The curve, unflattened

Whatever the catalyst was, it prompted some in Brown County to gather in multi-family groups. As they shared food or stories or huddled around a backyard fire pit, some unintentionally shared the coronavirus.

When some went to work a few days later, officials said, they kept sharing it, particularly in several meatpacking businesses that employ hundreds of people.

By April 13, the curve in Brown County coronavirus cases had been unflattened.

On April 17, the county acknowledged to the Press-Gazette it was calling in the Centers for Disease Control and Prevention. A cluster of cases, likely with one or more packing plants as its nexus, was causing case numbers to skyrocket.

It remains the only cluster heath officials have identified, Pritzl said. Before the meat industry spike, the virus had sickened people in dribs and drabs from multiple sources, some unknown.

Many were still going to work, even as more of their coworkers became ill. Some worked while sick.

Only after they knew of the cluster did the county ratchet up its social distancing message, and then not to the level of a Smokey Bear or an anti-tobacco scare campaign. Instead, Paprocki's warnings grew a tad more specific: "Don't go to church." "Don't take a cake to grandma's."

Pritzl wouldn't say Friday if the message should have been stronger. "You would know what an audience will react to better than I," he told a reporter.

The Public Health Department's focus had shifted to stopping a cluster that 10 days earlier had seemed almost unimaginable. Job 1, Casey said: Check meatpacking workers for symptoms.

As of April 20, Brown County's new trend was impossible to miss: With the fastest-growing rate of coronavirus cases among the state's 72 counties, the county's curve was spiking like nowhere else in Wisconsin.

Health officials examined JBS workers for symptoms as they arrived on Monday, using tents erected over the weekend to serve as exam rooms. Medical workers sent about 50 of JBS's 1,250 workers home the first day, Casey said.

The next day, roughly 30 more were sent home.

A county health official said American Foods began testing its workers beginning at 2 a.m., but would not say if any of those workers were sent home.

On Saturday, Brown County hit another milestone: The state reported 720 cases in the county, which now has the highest infection rate per capita in Wisconsin — about 277 people have come down with COVID-19 for every 100,000 residents.

Key dates in a county's epidemic

Milestones in the progression of coronavirus in Brown County:

March 17: Green Bay Mayor Eric Genrich decides March 17 that City Hall will close to the public the following day. Brown County had just one confirmed case of coronavirus, but the nation's death toll surpassed 100 and state health officials reduced the limit on people allowed to gather in one place to 10.

March 19: Brown County reported a second confirmed case and local hospital officials cautioned that people with symptoms should stay home unless they needed urgent care, to avoid spreading the infection in health care settings.

April 7: A significant loss of election workers because of fears about the virus, and a political battle over whether to postpone in-person voting prompts Green Bay officials to consolidate 31 polling places into two — one high school on each side of the Fox River. This results in massive lines at voting sites, forcing some people to stand outside for hours and prompting fears of a spike in coronavirus cases about two weeks later. As of Friday, county health officials said they have not connected an increase in cases to the voting situation, but say they continue to investigate.

April 9: A 58-year-old Green Bay man who had been infected with the virus died after at least a week in the hospital. He became the 111th coronavirus patient to die in Wisconsin since the virus arrived; 48 other county residents were infected.

April 10: Green Bay Police concede they're having to "scrounge, beg and borrow" for certain equipment to keep officers from safe from exposure while they're out in the community.

April 12: Easter Sunday. Health officials would say on April 23 that Easter is when a spike in cases began showing up in the county.

April 13: The county has its biggest weekend increase in cases to date: 30, bringing the total number of infected people in the county to 82, plus five members of the Oneida Nation. About a quarter of those infected were now in hospitals.

April 16: The county records another high for the pandemic: 139 cases. Most are in eastern Green Bay, Bellevue or Ashwaubenon. Most are believed to have been transmitted via "community spread" — by contact with someone locally.

April 17: A county health official, in a daily conference call with reporters, says there had been a "correlation of cluster of confirmed cases and specific locations where their operations are not accessible to the public," and that the department "anticipates additional resources to be deployed."

Later, the county tells the Press-Gazette the Centers for Disease Control and the state Department of Emergency Management will send people to Brown to join the probe.

April 20: As the county's total cases approach 300, health officials confirm what many local residents have suspected: There's a cluster of infections linked to the JBS Packerland beef-processing plant on Green Bay's southeast side.

April 22: Brown County reported a second person died from COVID-19, a 56-year-old woman.

April 23: The county's total cases shoot past 500. Though 267 of those link to local meatpacking plants, the health department says it has no plans to close any of the plants.

April 24: Brown County reports 618 coronavirus cases, 287 linked to meatpacking employees and their relatives. The U.S. Occupational Safety and Health Administration says it's investigating JBS and American Foods facilities.

April 25: The state Department of Health Services reports 720 cases in Brown County, which now has the highest infection rate per capita in Wisconsin.