On average, of every five HIV-infected urban gay men in the United Kingdom, two are undiagnosed, according to research from five major British cities presented to the Sixteenth International AIDS Conference in Toronto last week by the the Medical Research Council and University College London. Significantly, more than half of the undiagnosed men had received a recent negative HIV antibody test and had perceived themselves to be HIV-negative.
Gay men account for the overwhelming majority of HIV infections acquired in the UK. In addition, data suggest that high risk sex between men has increased significantly since 1998. However, increases in HIV incidence are difficult to ascertain from the raw number of gay men testing HIV antibody positive each year, since these may represent previously undiagnosed infections and/or increased voluntary HIV testing.
In order to better understand the connections between increased risk behaviour, increased HIV prevalence and undiagnosed HIV infection, investigators from the Medical Research Council's Social and Public Health Sciences Unit in Glasgow and the Centre for Sexual Health and HIV Research, at UCL, London, compared sexual risk behaviour and HIV prevalence in five major UK cities.
The investigators conducted cross-sectional surveys in bars, clubs and saunas frequented by gay men in London, Brighton and Manchester in 2003/4 and in Glasgow and Edinburgh in 2005. A total of 4384 men completed the questionnaires and 3661 provided oral fluid samples, for anonymous HIV testing utilising Orasure cheek swab kits. More men in Manchester (70.4%), Brighton (66.8%) and London (62.9%) agreed to anonymous HIV testing, however, than in Edinburgh (54.8%) and Glasgow (48.4%).
The city with the highest HIV prevalence was Brighton, where one in seven (13.7%; 95% CI, 10.6%-17.5%) of the men who agreed to anonymous HIV antibody testing were found to be HIV-infected. However, Brighton had the lowest percentage of undiagnosed men: one in three (33.3%) were unaware of their infection.
One in eight of the gay men in London (12.3%; 95% CI, 10.7%-14.1%) who agreed to anonymous HIV antibody testing were HIV-infected. However, worringly, London had the second-highest percentage of HIV-infected men unaware of their positive status, at 44.1%.
Although almost one in every two gay men in Glasgow who were HIV-infected were unaware of their positive status (48.1%), HIV prevalence was the lowest of the five cities. Just one gay man out every 28 who agreed to anonymous HIV testing was found to be HIV-infected in Scotland's most populous city (3.6%; 95% CI, 2.5%-5.2%).
Similar percentages of HIV-infected gay men in Manchester (36.7%) and Edinburgh (36.4%) were undiagnosed, although HIV prevalence was higher in Manchester (8.6%; 95% CI, 6.1%-12.0%), than in Edinburgh (5.5%; 95% CI, 3.9%-7.6%)
Taken together, 41.2% of HIV-infected gay men in all five cities who agreed to anonymous HIV testing were found to be undiagnosed. Over half of these men (53.4%) reported that their most recent HIV antibody test was negative and, consequently, they erroneously believed themselves to be HIV-negative.
The investigators also found a statistically significant link (all comparisons p<0.01 except where noted) between HIV status and risk behaviour. HIV-infected men were more likely than HIV-uninfected men to report unprotected anal intercourse (UAI) with multiple partners (34.8% vs 16.1%), UAI with casual partners (37.2% vs 22.2%), UAI with partners of unknown or different HIV status (32.3% vs 25.0%, p<0.05), and to have been diagnosed with a sexually transmitted infection (STI) in the previous year (39.1% vs 16.8%).
They conclude that "given the high level of sexual risk behaviour, undiagnosed infection and incorrect assumptions of status, the potential for HIV transmission is of concern" and argued that "targeted prevention efforts" are urgently required.