The key to building effective HIV prevention strategies Health Protection Agency (HPA) data suggest that by the end of 2012 more than 100 000 people will be living with HIV in the United Kingdom.1 Almost a quarter will be unaware of their infection. This figure may be small compared with countries in sub-Saharan Africa, but for a resource rich country it represents a serious failure in HIV prevention. Men who have sex with men (MSM) remain the group most at risk of acquiring HIV in the UK, North America, Australasia, and much of western Europe. Annual HIV diagnoses in MSM have doubled over the past decade, with about 3000 new diagnoses in the UK in 2010.1 One in four of these infections will probably have been acquired recently; and in men under 35 years, this figure is one in three. In London, one in 11 MSM is estimated to be HIV positive.1 Although at a population level no single intervention is likely to control HIV, effective prevention strategies should start with HIV testing. A negative test supports individual vigilance to remain uninfected. A positive test result opens up treatment options and enables …