Coverage of the COVID-19 pandemic, criminal justice and immigration.

An Arkansas county so rural it has just three incorporated towns and not a single stretch of interstate suddenly emerged this week as one of the nation’s coronavirus hotspots. Ground zero in Lincoln County, about an hour’s drive south of Little Rock, is the Cummins Unit, a state prison farm known for producing cotton, rice and eggs.

A farm employee was the first to test positive in early April. Now 14 staffers and more than 680 of the prison’s nearly 1,700 prisoners have the virus, according to test results reported this week.

What’s behind the surge in recorded cases? The state’s newly aggressive testing program. Rather than waiting to test for COVID-19 until people are obviously ill—or not testing at all—the state says it hopes to reduce the virus’s spread by tracking all cases, even for prisoners or staff who are asymptomatic.

“Nobody knows exactly how it acts,” spokeswoman Dina Tyler said of the virus. “It seems to bounce around more than a pinball.”

Only a handful of states have taken this expansive testing approach so far—but it seems responsible for a spike in reported coronavirus cases behind bars. Still, many prisons across the nation are only testing people who are evidently sick, not reporting any testing results for guards and other staff, or not testing at all, The Marshall Project has found. That could be a problem, health experts say, since undetected cases in prisons could contribute to community spread outside.

“Certainly for prisons who are taking the time, effort and resources to test everybody, not testing staff would be a bit of a blind spot,” said Barun Mathema, a professor of epidemiology at Columbia’s Mailman School of Public Health in New York. “The force of infection can be extraordinarily high in prisons.The most dynamic of that group is the people who work there.”

From California to North Carolina, prisons that do aggressive testing are finding that infection is spreading quickly. Take Ohio’s state prison system, which has two of the most serious outbreaks in the country. It has started mass testing of all staff and inmates at its most afflicted facilities.

Marion Correctional Institution, an hour north of Columbus, has reported four deaths, but has more than 2,000 prisoners and at least 160 staffers who tested positive for the virus. At Pickaway Correctional Institution an hour away, at least nine prisoners have died, while more than 1,500 prisoners and 79 staffers have tested positive.

“Because we are testing everyone—including those who are not showing symptoms—we are getting positive test results on individuals who otherwise would have never been tested because they were asymptomatic,” officials explained in an update on the Ohio Department of Rehabilitation and Corrections website. A spokeswoman did not respond to requests for comment.

States with the most robust testing identify the most cases, because they’re also finding people who have the virus but are not yet sick or are carriers who won't get sick at all, said Lauren Brinkley-Rubinstein, a faculty member at the Center for Health Equity Research in the University of North Carolina School of Medicine.

She’s also tracking cases of COVID-19 in state prisons—and how differently each state approaches testing. Prison guidelines from the Centers for Disease Control currently don’t recommend giving tests to people without symptoms, she said, “and this puts states in a tough spot,” especially in areas where tests are in short supply and people might resent the scarce tests going to prisoners.

But she said she thinks prisons should test as much as possible anyway. “If you identify who has it and who does not, you can apply better interventions,” she said. As for prisons that aren’t testing at all, Brinkley-Rubinstein said they are basically saying, “We’ll just deal with the carnage. Prisoners are consigned to oblivion.”

Officials we interviewed said their prisons had access to enough nasal swabs through local health departments or the companies they pay to manage healthcare in prison.

But some corrections departments did report a surprising gap: they aren’t testing guards. We found that in several states with significant COVID-19 outbreaks in prisons, including Michigan, California, Texas, New York and Pennsylvania.

Instead, in these states guards are expected to arrange for their own tests in the community—from a doctor, clinic or health department—and report the results to corrections officials. Some states are then publishing data about staff infections.

This week, state and contract nurses arrived at the Lakeland prison in Michigan near the Indiana border, where 112 prisoners had tested positive for coronavirus. Nine men have died, all from the geriatric wings housing 393 people. The nurses’ job: make sure all 1,400 prisoners at Lakeland get tested for COVID-19.

"We felt strongly from the beginning that to solve a problem we have to know where it is,” said Chris Gautz, spokesman for the state prison system. “You have to test in order to fix it."

The tests found that the virus covers Lakeland like a blanket, with 73 percent of the first 535 inmates testing positive.

But the agency isn’t testing its own staff, though two Michigan corrections officers have died from the virus. The Detroit News reported that at least 210 of the state’s 12,000 corrections staff have tested positive. The department, like most states, relies on staff getting tested elsewhere if they show symptoms.

Detroit’s health department is now offering free tests to prison workers on weekends, Gautz said.

Louisiana reported the death of a prison warden and a medical director this week. A corrections department spokesman did not respond to questions from The Marshall Project about whether Louisiana prisons are testing staff.

The state is home to one of the worst outbreaks in the federal prison system in Oakdale, where 11 men have died. Federal officials have largely given up testing at a half dozen prisons where serious outbreaks have erupted, saying they assume that all staff and prisoners have been exposed: What’s the point of testing? Why waste the limited swabs?

When coronavirus cases began to spike at North Carolina’s Neuse Correctional Institution, 60 miles southeast of Raleigh, prison officials took the opposite approach, testing all 700 inmates and 250 staff.

They found at least 65 percent of the prisoners have the virus, a number that may increase as all results come in. Notably, 98 percent of those infected were not showing symptoms, said John Bull, a corrections department spokesman.

To deal with the crisis, the state has closed a prison in nearby Johnston County, shipping the men who were held there to other facilities while moving the entire prison staff to Neuse.

North Carolina is unlikely to repeat the test-everyone approach now that everyone realizes how serious the problem is, Bull said. "Every other warden in the North Carolina prison system is paying very, very close attention now."

This week, public health officials in California broadened guidelines on who should be tested for coronavirus, recommending for the first time that asymptomatic people living or working in high-risk settings—such as prisons—should be a priority.

That led officials to test more than 100 prisoners at the California State Prison in Los Angeles County—which yielded a spike in the number of reported cases.

“These asymptomatic patients do not represent a new outbreak,” said Dana Simas, a spokeswoman for the prison system. “But it’ll help us identify who is negative and help us identify better medical care and housing needs for those who are positive.”

California, however, is not including prison staff in those tests.