All five were drug users sharing needles while they were in Glenochil prison, central Scotland, where 14 prisoners were found to be HIV-positive last year.
The survey attributed part of the outbreak to the 'misfortune' of one drug-using prisoner sharing needles with others at a time when he was highly infectious.
The survey, a follow-up to investigations carried out last year, took the form of voluntary saliva tests and questionnaires from prisoners who were assured of anonymity. A total of 84 per cent of the 352 prisoners responded - the highest response rate for any prison in Scotland or England, the Scottish Prison Service said.
Seven men gave positive saliva tests, all of them drug injectors and all but one of them from Glasgow. Roughly one in three prisoners said they had injected drugs at some time and a quarter of those injecting said they had started doing so in prison. The survey found the extent of HIV and drugs misuse was roughly in line with other Scottish prisons, although Glenochil had a higher concentration of injectors.
A member of the survey team, Dr Graham Bird, of the department of immunology at Churchill hospital, Oxford, said: 'We are concerned about this finding.
'Prison staff and prisoners need to work together to understand why this happens, for example by asking injector inmates what would have prevented them from starting to inject inside.'
Some of the 14 prisoners who tested HIV positive at Glenochil last year have since completed their sentences; some of them may have been HIV positive when they arrived at the jail.
Of the seven who tested positive in the voluntary saliva test, five were in Glenochil at the time of the outbreak last year and were injecting drug users. A sixth was not at Glenochil last year, and the seventh was at Glenochil but said he was not an injecting drug user at that time.
If there had been a 100 per cent response to the latest survey, researchers estimate it would show a total of eight or nine HIV-positive prisoners.
The head of the inquiry team, Dr Sheila Gore, of the Medical Research Biostatistics unit at Cambridge, said the survey indicated drug-injecting behaviour at Glenochil was similar to other jails. 'That last year's outbreak took place at Glenochil was probably due to the misfortune of one HIV-infected man involved in a needle-sharing network when he was very infectious.'
The Scottish Prison Service has already launched drug-reduction programmes at Glenochil and Edinburgh and is due to launch a similar programmme at Perth.Reuse content