LOUISVILLE, Ky. — On March 15, a church revival held in the heart of Western Kentucky to radiate joy and love unintentionally passed around something far more sinister — the novel coronavirus.

Like a pebble tossed in a pond, the virus rippled throughout the region, helping turn the area within weeks into a hot spot for COVID-19 — and giving Hopkins County the second-highest infection and death rate in Kentucky.

One large get-together, one unguarded moment, and an entire region can become infected.

"A single mass gathering that's held right now — pick your county — can blow up like we have seen in some of these areas," Kentucky Gov. Andy Beshear said Thursday at his daily coronavirus briefing.

A Courier Journal analysis of virus hot spots around the region, including in Indiana and Tennessee, shows that Beshear is right.

The counties struggling now with the highest coronavirus rates often aren't large urban centers, they're more rural and suburban — including some with large facilities housing high-risk people such as inmates or the infirm.

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SEARCH: Our interactive map shows you death, cases and rates for every U.S. county

While the official data is far from uniform — states have different methods and success at reporting complete testing numbers — it provides insight into where the pandemic is hitting states the hardest, and why.

In 120-county Kentucky, four of the six counties with the highest rates of infection are clustered in the west. Near the top is Hopkins County, home of the church revival, with 181 coronavirus cases for every 100,000 residents.

Citing an additional COVID-19 outbreak this week at a state psychiatric hospital and prison in the same region, Beshear spoke out about his identified the Western Kentucky counties with its high rates of coronavirus cases "a great concern."

"Everywhere that we have a cluster — and that's what we would call this — is of significant concern," Beshear said.

Jackson County, southeast of Lexington, served as a chilling example of how fast COVID-19 can spread.

On Monday, the county did not have a single confirmed case, but on Friday, the local health department announced 41 confirmed cases, all but one a resident or staff member of a nursing home.

In four days, Jackson's County infection rate went from 0 to 305 cases per 100,000 residents, surpassing Hopkins County as the worst hot spot in Kentucky.

The infection rates are even worse in Southern Indiana and North Central Tennessee, where clusters of rural and suburban counties near the Kentucky and Ohio borders have infection rates up to two times higher than Hopkins County.

Kentucky coronavirus live updates:Follow along for the latest news

Many of those counties' residents commute across county lines to work in more populated areas, such as Cincinnati and Nashville.

Tennessee's Sumner County, which lies on Nashville's fringe, has an infection rate of 230 positive COVID-19 cases for every 100,000 residents, and it has reported 21 deaths — despite a population of about 180,000.

In Southern Indiana, a trio of counties between Cincinnati and Indianapolis is plagued with even higher infection rates, led by Decatur County with a rate of 444 positive tests per 100,000 residents. Adjoining Franklin and Ripley counties reported the second- and third-highest infection rates in Indiana.

The three counties between them have seen at least 18 confirmed COVID-19 deaths, despite having a combined population of roughly 78,000.

Some communities that faced early COVID-19 outbreaks, such as Kentucky's Harrison County, are seeing signs they have "flattened the curve" of rising cases thanks to weeks of aggressive social isolation.

But clusters of hot spot counties within the cluster of Kentucky, Tennessee and Indiana all face a critical challenge in the coming weeks as their cases and deaths continue to rise.

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Here's a closer look at the hot spots:

Hopkins County tries to beat back the surge

On March 27, the Kentucky Department of Public Health's records only showed two confirmed cases of the coronavirus in Hopkins County.

By Friday, two weeks later, the official tally for Hopkins County had spiked to 83 confirmed cases, according to the Hopkins County Health Department.

Madisonville Mayor Kevin Cotton and Hopkins County Judge-Executive Jack Whitfield Jr. have begun a live daily briefing to update the surge in cases, offer tips for social distancing and give shoutouts to those working to "flatten the curve."

In their Monday morning video, Whitaker highlighted a New York Times map that showed Hopkins County as "the fastest-growing COVID-19 county in the state. … We don't want that recognition."

The week before, local officials detailed how the revival services held days after Beshear asked churches not to hold in-person services have been linked to 54 confirmed COVID-19 cases and six deaths there.

Cases linked to the revival have extended to neighboring Muhlenberg County and other counties farther east, with a nursing home, business and an ambulance service all linked to the outbreak.

Related:Church responds to 'unjust criticism' about revival at center of outbreak

Rising infections in Western Kentucky

Bordering Hopkins County, Muhlenberg County is one of several counties nearby in the Western Kentucky region with high rates of COVID-19 cases.

The local health department counts 40 confirmed cases, vaulting Muhlenberg to No. 4 with an infection rate of 129 cases per 100,000 residents.

Muhlenberg was No. 2 until Friday, when Jackson County's cases surged and Adair County officials announced its cases had leaped from six to at least 32 because of an outbreak at the county’s only nursing home.

Muhlenberg County Judge-Executive Curtis McGehee told The Courier Journal that Monday "was our worst day as far as numbers coming in, so I don't know where the turning point is on this."

With four of its cases linked to Hopkins County's church revival, Muhlenberg County was also rocked by Beshear's recent announcement that its Green River Correctional Complex had 10 state inmates and seven staff test positive for COVID-19.

Likewise, neighboring Christian County, just south of Hopkins County, got word that nine residents and 10 staff members at Western State Hospital — a state psychiatric facility there — had tested positive for the coronavirus, with two patients dying Wednesday.

And in nearby Lyon County, one county removed from Hopkins, saw its two deaths from the coronavirus during at outbreak at its River’s Bend Retirement Community.

List:These Kentucky nursing homes have reported coronavirus cases, deaths

'We want to be good neighbors'

As Muhlenberg County's numbers crept up, McGehee enacted a countywide 9 p.m. curfew to "prevent congregating" that had been happening in parking lots at night.

While most follow social distancing orders, McGehee said, "we do have some people that still are not taking it seriously."

"Right now our community is very fragile and volatile, and we're trying to do everything we can to take steps in the right direction to get this slowed down," he said.

Muhlenberg County Health Department Director Cathy Bethel said that while nearly half of its COVID-19 cases stem from its state prison, many residents travel to surrounding counties for work, including nurses who work in hospitals.

The Green River facility has implemented extra measures to prevent the further spread of the coronavirus, including extensive inmate monitoring, staff testing and cleaning of high-touch surfaces.

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Troubles in Tennessee's Sumner County

In nearby Simpson County, which is wrestling with its own outbreak of COVID-19, Judge-Executive Mason Barnes told The Courier Journal his county is "winning a race we don't want to win."

Barnes named his prime suspect as Simpson County's southern neighbor: Tennessee's Sumner County, which had 413 confirmed cases Saturday and the highest infection rate in Tennessee.

"We get this influx of Tennessee folks up here to our grocery stores and so forth, and they could bring the virus with them," said Barnes, adding that Tennessee was weeks behind Kentucky on enacting stricter rules to curb social interaction.

"We just took more proactive steps in Kentucky sooner than Tennessee did, and living on the Tennessee border right here with I-65, I can't keep the people from coming up here and taking advantage of the tax breaks they get on items and groceries."

Barnes said he would like Beshear to consider closing the border for those only coming to shop in Kentucky.

Next door to Sumner County, Tennessee’s Trousdale County, has seen its own troubles with COVID-19, particularly because it's only about an hour northeast of bustling Nashville.

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Some county residents doubted the virus would trouble their more sparsely populated communities.

“There was a thought,” said Stephen Chambers, Trousdale's county mayor. “We’re a small community. We’re spread out in population … how spread out we are would kind of protect us.”

But with 14 confirmed COVID-19 cases and one death as of Saturday — a 74-year-old man who worked at Trousdale Medical Center — the county is among the state's hardest hit when measured by per capita infections and deaths.

“It really drove it home once the gentleman passed … people knew him,” Chambers said.

Still, with its “significant number” of residents working in neighboring counties with larger populations, the county's outbreak isn't surprising, he said.

Trousdale County has been under an emergency order since its first confirmed case March 28, and most appear to be heeding calls to stay home whenever possible, Chambers said.

It’s mainly younger residents who need reminding, Chambers said. “When you’re younger you think you’re 10-foot-tall and bulletproof.”

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Indiana's commuting virus

Even more problematic are Decatur, Ripley and Franklin counties in Southeast Indiana near Cincinnati — all of which have infection rates well above any other Indiana county and at least double that of Kentucky's Hopkins County.

Ripley County Health Officer Dr. David Welsh told The Courier Journal the three-county area is a hot spot for the coronavirus pandemic, as its rate is far above nearby counties that are similarly populated.

With seven coronavirus fatalities, Franklin County had the highest death rate in the state. Decatur County, which had eight deaths as of Saturday, was second.

"Between Ripley, Franklin and Decatur, there’s two critical access hospitals, so there’s a total of 50 beds for just over 75,000 people," Ripley said of the area's capacity to treat a large surge of coronavirus patients. "That’s the other part of the equation to be concerned."

The Indiana cluster of counties also has a large number of residents who work in cities such as Indianapolis and Cincinnati and businesses with a national and international reach — giving them greater exposure to the virus.

Despite that, Welsh said he still gets reports of large gatherings.

"There are still some folks who don’t recognize this as a serious public health crisis," he said.

Jason Lovins, spokesman for the Franklin County COVID-19 task force, said the area's cases still haven't peaked.

"We are still alarmed," Lovins said. "… but if you look at our rate of incline, knock on wood, it appears to have slowed down."

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A Kentucky model and 'false sense of security'

One county hoping it has hit that plateau is Kentucky's Harrison County, just north of Lexington, where the commonwealth's first confirmed case of COVID-19 was announced on March 6.

Over a month later, Harrison County still has an infection rate of 75 cases per 100,000 residents, but it's fallen out of the top five highest counties.

But Cynthiana Mayor James Smith said Harrison County has only picked up a few new cases over the past two weeks, two of which are for tests nearly two weeks old.

"We're pretty flat over here, especially from our first week or two," Smith said.

For Smith, it's a sign that the county and Cynthiana may now be seeing the dividends from its early investment in social distancing — making it a model for counties now dealing with a spike in infections.

"We were one week ahead of everybody else," Smith said. "Plus, our folks really responded here. We don't have a lot of people violating our orders.

"It's been good to brag on the city, because they have done really well."

Looking back: Cynthiana became state's epicenter for coronavirus, but life goes on

Reach reporter Joe Sonka at jsonka@courierjournal.com; 502-582-4472; Twitter: @joesonka. Reach Jonathon Bullington at 502-582-4241; JBullington@courierjournal.com; Twitter: @jrbullington. Reach David Kim at DKim@courierjournal.com; Twitter: @_DavidJKim.

Coronavirus hot spots

Below are the top five counties in Kentucky, Indiana, Ohio and Tennesse with the highest COVID-19 infection rates as of Saturday afternoon (confirmed cases per 100,000 residents). Source: Johns Hopkins University COVID-19 tracking project; Kentucky health departments.

Kentucky

Jackson: 305 positives per 100,000 residents (41 positive cases; 0 deaths) Hopkins: 181 positives per 100,000 residents (77 cases; 6 deaths) Adair: 166 positives per 100,000 residents (32 cases; 1 death) Muhlenberg: 129 positives per 100,000 residents (40 cases; 0 deaths) Lyon: 98 positives per 100,000 residents (8 cases; 2 deaths)

Indiana

Decatur: 444 positives per 100,000 residents (118 cases; 8 deaths) Franklin: 289 positives per 100,000 residents (66 cases; 7 deaths) Ripley: 278 positives per 100,000 residents (79 cases; 3 deaths) Marion (Indianapolis): 275 positives per 100,000 residents (2,600 cases; 107 deaths) Hendricks: 178 positives per 100,000 residents (287 cases; 8 deaths)

Tennessee

Sumner: 230 positives per 100,000 residents (413 cases; 21 deaths) Davidson (Nashville): 153 positives per 100,000 residents (1,048 cases; 13 deaths) Trousdale: 146 positives per 100,000 residents (14 cases; 1 death) Williamson: 137 positives per 100,000 residents (299 cases; 4 deaths) Grundy: 143 positives per 100,000 residents (19 cases; 0 deaths)

Ohio