One in three HIV positive gay men has unprotected sex and one in five HIV negative gay men do the same, a survey suggests.
Researchers surveyed 2,640 men at 60 gay venues in London, Manchester and Brighton between 2003 and 2004.
The rate of HIV infection was highest in Brighton, at almost 14%, and lowest in Manchester, at 8.6%, the authors found.
But the rate of undiagnosed infection was high in all three cities, ranging from one in three in Brighton to more than four out of 10 in London.
The authors, from University London, said called for renewed efforts to be curb risk behaviours that encouraged onward transmission of HIV and other sexually transmitted infections.
Sexually Transmitted Infections (2007) www.stijournal.com