NEW YORK (NYTIMES) - The coronavirus is spreading quickly in America's jails and prisons, where social distancing is impossible and sanitiser is widely banned, prompting authorities across the country to release thousands of inmates in recent weeks to try to slow the infection, save lives and preserve medical resources.

Hundreds of Covid-19 diagnoses have been confirmed at local, state and federal correctional facilities - almost certainly an undercount given a lack of testing and the virus's rapid spread - leading to hunger strikes in immigrant detention centers and demands for more protection from prison employee unions.

A week ago, the Cook County jail in Chicago had two diagnoses. By Sunday (March 29), 101 inmates and a dozen employees had tested positive for the virus.

A nearby Illinois state prison reported a coronavirus-related death on Monday, and Michigan prisons reported 78 positive tests.

The Rikers Island jail complex in New York City had at least 167 confirmed cases among inmates by Monday. And at least 38 inmates and employees in the federal prison system have the virus, with one prisoner dead in Louisiana.

"It's very concerning as a parent," said William Brewer Jr, whose son is serving time for robbery in Virginia. "He's in there sleeping in an open bay with 60 other people. There's no way they can isolate and get 6 feet between each other."

Defence lawyers, elected officials, health experts and even some prosecutors have warned that efforts to release inmates and to contain the spread of the disease are moving too slowly in the face of a contagion that has so far infected more than 150,000 people in the United States, with more than 2,500 deaths.

"By keeping more people in the jails, you are increasing the overall number of people who contract the virus," and the demand for hospital beds, ventilators and other lifesaving resources, said David E. Patton, head of the federal public defender's office in New York City, which represents nearly half of the 2,500 inmates in the city's two federal jails.

"They are playing roulette with people's lives."

America has more people behind bars than any other nation. Its correctional facilities are frequently crowded and unsanitary, filled with an aging population of often impoverished people with a history of poor health care, many of whom suffer from respiratory and heart problems.

Practices urged elsewhere to slow the spread of the virus - avoiding crowds, frequent hand washing, disinfecting clothing - are nearly impossible to implement inside.

"Even as a visitor," Brewer said, "if you want to wash your hands, you've got to walk out and go into another building to do it."

The Federal Bureau of Prisons, which holds more than 167,000 people nationwide, has been criticised by its own employees as slow to act.

On Friday, dozens of public health experts sent a letter to President Donald Trump urging him to take immediate steps to protect inmates and immigration detainees.

Attorney General William Barr said officials were trying to expand home confinement, as opposed to directly releasing federal prisoners, almost all of whom were convicted of felonies. He ordered an assessment of at-risk nonviolent inmates, particularly those who have served much of their sentence.

But it was unclear how many would qualify under a complex list of criteria. And Barr cautioned that the review would not result in immediate transfers because of the need to ensure that prisoners would not spread the virus once freed.

In Chicago, as the number of positive test results at the county jail have skyrocketed, Sheriff Tom Dart has established a quarantine area for those who have the virus and another one for those showing symptoms who have not tested positive but need to be monitored. The most serious patients are being taken to the hospital.

"Our jails are petri dishes," said Toni Preckwinkle, president of the Cook County Board of Commissioners, comparing them to nursing homes or cruise ships - both places where the virus has spread rapidly.

She said officials are seeking to reduce the jail's population to 4,000 people, from about 6,000 before the outbreak began. Currently, the population stands at about 5,000. Only inmates accused of nonviolent crimes are eligible for release, she said.

In Cleveland, the legal system was quick to act as the coronavirus took hold in the United States, cutting the county jail population in half, to about 1,000 people, since March 12.

In New York City, where the jail system's chief physician warned several days ago that "a storm is coming," Mayor Bill de Blasio said the city had released at least 650 people by Sunday from Rikers Island, the city's main jail complex. Most of those inmates were convicted of nonviolent crimes and serving sentences of less than a year. Hundreds more were under review for possible release.

In Los Angeles County, Sheriff Alex Villanueva has embarked on what appears to be the largest US effort to release inmates, freeing 1,700 people this month, or about 10 per cent of the population of one of the nation's largest jail systems.

California has the second-largest prison population in the country, after Texas, and at least 12 California state prison employees have tested positive for the coronavirus.

Staff and inmates have also tested positive at correctional facilities in Florida, Texas, Michigan, Pennsylvania, New York and Washington, among others, and advocates said there are almost certainly many undetected cases across the country.

Unlike county jails, where most inmates are either serving sentences for minor crimes or are awaiting trial, state prisons - which hold the majority of the nation's 2.3 million incarcerated people, most of whom were convicted of felonies - are less likely to make large-scale releases.