As the United States grapples with the coronavirus pandemic, there is concern not only for the elderly but also for another vulnerable population: prisoners.

The US has the highest rate of incarceration in the world and experts have warned that infections could potentially spread rapidly in the country's crowded prisons.

Christopher Blackwell, 38, is serving a 45-year sentence for murder and robbery at a facility in Washington state, which has the most new-coronavirus deaths in the country.

In an article published by The Marshall Project, a group that advocates for criminal justice reform, Blackwell said he was "not surprised" to learn last week a prison employee had tested positive for COVID-19.

He also said he was not reassured by the response of the Washington State Reformatory authorities.

"They posted signs down by the phones instructing us to put a sock -- yes, like you wear on your foot -- over the phone receiver before using it in order to avoid spreading germs," Blackwell said.

Inmates had been advised to maintain cleanliness but alcohol-based hand sanitizer is banned and even rags are hard to come by, he said.

Blackwell was particularly worried about elderly inmates, including a friend in his 80s who he identified as "Bill."

"Bill is one of the many prisoners currently under lockdown," Blackwell said. "He, and people like him, are in severe danger.

"How can we protect people like Bill in a place many have referred to as a 'tinderbox' for a virus like COVID-19?" he asked.

The US has some 2.2 million people behind bars, nearly one-fourth of the world's entire prison population.

Civil rights groups, doctors and lawmakers have been sounding the alarm about the deadly potential of coronavirus spread behind prison walls.

Fifteen Democratic senators wrote a letter last week to the federal Bureau of Prisons asking what measures were being taken to protect inmates.

"Given the spread of the virus in the US -- and the particular vulnerability of the prison population and correctional staff -- it is critical that BOP has a plan," they said.

Their appeal gained urgency this week when the local press reported guards have tested positive for coronavirus at Rikers Island and Sing Sing prisons in New York state.

- 'Ground zero' -
 

Federal prisons hold about 175,000 inmates and most of the US prison population is housed in state facilities or local jails.

The American Civil Liberties Union (ACLU) sent letters to federal, state and local officials on Wednesday with recommendations for "immediate action."

The ACLU called on governors to commute the sentences of prisoners considered "particularly vulnerable" to the virus whose prison terms were scheduled to end in the next two years.

It asked police to stop arresting people for minor offenses, prosecutors to seek pretrial detention whenever possible and judges to hold more hearings by telephone or video conference.

"Public health experts recognize that there is a heightened risk of infection for people who are involved in the criminal legal system," said Udi Ofer, director of the ACLU's Justice Division. "Downsizing the footprint of the criminal legal system should be a part of the COVID-19 public health response."

Gregg Gonsalves, an assistant professor at the Yale School of Public Health, warned that prisons could be "ground zero for the pandemic."

"It's really a perfect storm of problems for the COVID outbreak and prisons in the US," Gonsalves told AFP.

"And so what everybody is saying now is, try to make it more hygienic but you've got to lower the prison population," he said.

"If you have elderly prisoners who are non-violent offenders, let them leave the prison because it's more dangerous for them inside than it is outside."

For the moment, the authorities, besides stressing cleanliness and isolating vulnerable prisoners, have also cancelled prison visits.

That measure does not come without risks -- 12 inmates died in prison riots in Italy and two in Jordan after similar restrictions were put in place.

Gonsalves described it as a potential "make or break moment for how we treat prisoners in the US," with the country confronted by a virus that does "not respect prison walls."