This has sparked fears in Ireland that the disease may be spreading amongst the wider community at a faster rate.
Around 3,500 HIV infections have been reported in Ireland. It is reckoned, however, that one in three people already infected with the virus are unaware of their disease status.
Executive director of Dublin AIDS Alliance, Ann Nolan, said there was already anecdotal evidence that people were presenting themselves for diagnosis at a late stage.
“It is really down to a huge lack of awareness of HIV and AIDS among the general population,” said Ms Nolan, who heads the voluntary group that provides support, advocacy and mediation services for people affected by HIV/AIDS.
Researchers found that in a large number of cases patients were going to their doctor with HIV-related symptoms, but still remained undiagnosed as much as a year later.
“As a result, there is a chance that they will not be picked up as a result,” she pointed out.
The researchers, writing in the British Medical Journal, have called for routine HIV screening to increase, with those most at risk encouraged to take a test.
Less than half of the patients (41%) were diagnosed as part of routine screening, according to the team from Chelsea and Westminister NHS Trust.
They also pointed to the well-recognised advantages of early diagnosis of HIV and starting appropriate treatment with highly active anti-retroviral therapy.
Ms Nolan said gay men and injecting drug users were aware of the HIV-risk and were linked into the services.
“They are more likely to look after their sexual health and be detected for HIV,” she added.
What the research demonstrates yet again was the real need for a national campaign around HIV, said Ms Nolan.
“People are incredibly apathetic about HIV because they associate it with purely at-risk groups and don’t perceive themselves to be at risk at all,” said Ms Nolan.
There was also a need for an awareness for clinicians who are not specifically dealing with HIV infection.
And, she warned that the dramatic rise in sexually transmitted diseases (STDs) was not helping matters.
“That may herald an increase in HIV as has been the case in other countries because the virus is more easily transmitted where there is a sexually transmitted infection.”