In the UK, the majority of the HIV-positive gay and bisexual men who are likely to transmit HIV remain undiagnosed, Valerie Delpech of the Health Protection Agency said on Monday. Moreover, modelling work suggests that 48% of all new infections in gay and bisexual men are acquired from men with undiagnosed primary HIV infection and 34% from men with undiagnosed long-term infection.
Speaking to the IAPAC meeting on “controlling the HIV epidemic with antiretrovirals”, she warned that good access to antiretrovirals in the UK has not led to a reduction in new infections. “This is due to the undiagnosed fraction and particularly men in primary infection,” she said.
Dr Delpech suggested that the situation in the UK provides useful insights into what is possible when other countries expand their access to antiretroviral treatment, perhaps motivated by considerations of ‘treatment as prevention’ (TasP).
In the context of the UK's free, open-access healthcare system, over 95% of people newly diagnosed with HIV are connected with specialist care within three months and over 95% of people who attend during one year are retained in care the following year. Moreover 87% of people with a CD4 cell count below 350 cells/mm3 are taking antiretroviral treatment. Few other countries have comparable results.
The area in which the UK performs more poorly is testing and diagnosis. One quarter of people who have HIV are undiagnosed and one half of people with HIV are diagnosed late, in other words when they already need HIV treatment (CD4 cell count below 350 cells/mm3). These figures have not changed much over the past decade.
It is thought that only 15-25% of gay and bisexual men take an HIV test in any given year.
Modelling work by Paul Birrell of the Medical Research Council (unpublished at present) suggests that the annual number of new HIV infections in gay and bisexual men (incidence) changed very little between 2001 and 2010, with between 2000 and 3000 new infections each year.
Dr Delpech commented: “Despite substantial progress of ‘test and treat’ prevention policies over the past decade in the UK, there is no evidence of a reduction in the incidence of HIV infection in men who have sex with men.”
In order to begin to explain this, she showed analyses prepared by her Health Protection Agency colleague Alison Brown, who wished to estimate the number of men who are ‘infective’, in other words have a viral load above 1500 copies/ml, and so would be more likely to transmit the virus.
Dr Brown found that of approximately 40,000 HIV-positive gay and bisexual men living in the UK in 2010, one third (35%) were infective. But, importantly, 62% of those who were infective remained undiagnosed.
Of those remaining, just 5% had a CD4 cell count below 350 cells/mm3 but weren’t taking treatment. A further 12% had CD4 cell counts between 350 and 500 cells/mm3 and 16% had a CD4 cell count above 500 cells/mm3. Finally 5% were taking treatment but had not yet suppressed the virus.
So, although the number of people taking treatment could be increased, this wouldn’t make a substantial difference to the epidemic. Dr Brown found that changing guidelines so that treatment was recommended for all with a CD4 cell count below 500 cells/mm3 would only reduce the proportion of infective men from 35% to 29%.
Dr Delpech then presented further unpublished modelling work, this time prepared by Andrew Phillips of University College London. This individual-based stochastic computer simulation model incorporates an extensive range of behavioural and public health surveillance data collected over three decades.
The model aims to estimate new infections, disease progression and the effect of antiretroviral therapy in gay and bisexual men in the UK.