Prisoners at the city's main jail are not declaring if they start getting coronavirus symptoms fearing they could lose their basic benefits.
A worrying new trend at HMP Liverpool has been spotted with inmates not keen to flag up any sign of Covid-19 because self-isolation might signal an end to their daily shower, time exercising outside and phone call to a loved one.
Officers described the emerging tactic at the Walton facility as "a huge worry" amid concerns such behaviour could lead to a large rise of new cases.
So far at HMP Liverpool, there have been no deaths, compared to two fatalities at the city's other major jail, HMP Altcourse in Fazakerley.
The ECHO understands about eight members of staff have tested positive at HMP Liverpool since proper testing was introduced about 10 days ago.
A more rigorous blood test is now being used, instead of a thermometer-type check which was previously employed by some jails.
Sources close to the Merseyside prison scene believe HMP Liverpool, Altcourse, and Risley and Thorn Cross in Warrington are about "two weeks behind normal society", with a likelihood the virus could take a real grip at the start of May.
The problem of prisoners hiding symptoms has been highlighted with governors at those Liverpool and Warrington jails, but the general consensus is not much can be done to stop it.
An insider told the the ECHO: "It's a huge worry.
"How do you get round it?
"It's down to prisoners' personal responsibility.
"There's no way of knowing, truly, how many prisoners have coronavirus.
"We won't be at all surprised if there is a build-up over the coming weeks.
"It's also worth remembering that most prisoners are relatively young and fit, under the age of 35, and can cope with it.
"Nobody is panicking, things are going far better than was expected.
"But we won't get a proper reflection unless if prisoners don't come out and declare symptoms."
The Ministry of Justice declined to comment.
Both deaths of prisoners in custody at Altcourse, run by private security firm G4S, were inmates already seriously ill.
One had terminal cancer, 57, while another, 74, was extremely poorly whose death was expected.
Both were moved from Altcourse and died in a hospice and Aintree Hospital respectively.
Almost 300 prisoners have tested positive for coronavirus in more than half of jails in England and Wales.
There are now a total of 278 confirmed cases in 64 prisons as of 5pm on Sunday, according to the Ministry of Justice (MoJ), and 13 inmates have died.
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Some 194 prison staff have also contracted the virus in 53 jails as well as eight prisoner escort and custody services staff.
Some 700 staff have been tested and 6,268 were self-isolating, according to the latest available figures.