More than one in three HIV positive gay men say they have unprotected sex, a survey reveals.
The surveys were carried out at 90 gay bars, clubs and saunas in London, Manchester and Brighton.
Over 2,000 men provided saliva samples. Of these, one in three of the men with HIV did not know they had the virus.
The figure was much higher in London, where 44% of HIV positive men were undiagnosed.
Over 37% of HIV positive men have had unprotected sex with more than one partner in the past year, says the survey in the journal Sexually Transmitted Infections.
And figures show that almost one in five men without HIV do the same.
Will Nutland, Head of Health Promotion at Terrence Higgins Trust said: “Although the number of HIV positive gay men having unprotected sex appears high, it’s important to look behind the headlines.
“The Gay Men’s Sex Survey shows that these men are more likely to have unprotected sex with other HIV positive men, rather than with those who don’t have the virus.
He added: “The new research also backs up other evidence which demonstrates the need for ongoing, targeted HIV prevention work with gay and bisexual men in the UK.”
The rate of HIV infection was highest in Brighton, at almost 14%, and lowest in Manchester at 8.6%.
Mr Nutland said: “The number of gay men with undiagnosed HIV infection is not reducing. Large numbers, especially in the UK’s major cities, have HIV and don’t know it.”
This was despite the fact that over two thirds of these men said they had been to a sexual health clinic within the past year.