On the 30 June 2013, the WHO produced new HIV treatment guidelines that recommend that antiretroviral therapy (ART) begins when CD4+ cell counts reach below 500 cells/μl . This change (from starting treatment at <350) is motivated by recent evidence of the public health benefits of treatment in addition to clinical benefits for individual patients. Patients treated successfully so that their viral load is undetectable (<50 copies/ml) have a negligible risk of passing their infection onwards through unprotected sex .
We previously published research that described the proportion of MSM between 2007 and 2010 in the UK who were ‘infectious’, over which period ART coverage increased . We apply this methodology to the 2011 UK HIV population to specifically address the potential impact of the WHO guidelines on the viral load of people living with HIV in the UK.
Overall, an estimated 96 000 [95% confidence interval (CI) 90 100–102 500] people were living with HIV (PLWHIV) in the UK in 2011, of whom 24% (95% CI 19–28%) were unaware of their infection . ART coverage was already 84% (61 300/73 700) among the HIV-diagnosed population that year . The most recent British HIV Association guidelines (2012) recommend initiating ART at 350 cells/μl, and also indicated that treatment be discussed with patients with higher CD4+ cell counts to prevent transmission to HIV-negative partners . HIV care and treatment is free and accessible in the UK, and engagement and retention in care following diagnosis is extremely high. At least 97% are integrated into HIV care within 3 months of diagnosis and 96% are retained in care annually .
National surveillance data  were combined with modelled estimates of undiagnosed HIV prevalence  using methods described previously . The percentage of patients with detectable viral loads by diagnostic, treatment and CD4+ status was applied to the HIV population. Overall, an estimated 42% (40 800/96 000) of all PLWHIV had detectable viral loads (>50 copies/ml) in 2011, with 26% (18 800/73 400) among the diagnosed population. Among MSM, 41% had a detectable viral load, compared to 46% and 43% among heterosexual men and women, respectively.
Overall, 54% (22 000/40 800) of all PLWHIV with detectable viral loads were undiagnosed, 28% (11 550) were diagnosed but untreated and 18% (7250) were diagnosed and treated in 2011. Treated patients include those who had recently begun ART and also those with suboptimal adherence. Among the 11 550 PLWHIV who were diagnosed but untreated, 2000 (17%) had CD4+ cell counts below 350 cells (and therefore should have been receiving treatment), 3600 (31%) had CD4+ cell counts between 350 and 499 cells (and should therefore be treated according to the WHO guidelines) and 5950 (52%) had CD4+ cell counts above 500 cells at the date they last accessed care.
We estimate that, if all diagnosed and untreated patients with CD4+ cell counts below 500 cells/ μl were treated (assuming 12% of treated MSM had detectable viraemia for the reasons stated above), the proportion of all 96 000 PLWHIV with detectable viral loads could have decreased from 42% (40 800) to 38% (36 500) [and from 26% (18 800) to 20% (14 500) among the diagnosed population]. Consequently, the WHO guidelines are likely to have limited impact on HIV transmission in the UK. In contrast, halving the undiagnosed population from 22 600 to 11 300 could have led to a decrease in the proportion of PLWHIV with detectable viral load from 42% to 28% (27 000). This analysis does not take into account the complex dynamics of HIV transmission (such as number of partners and condom use). Nevertheless, they provide a population level understanding of the possible impact of shifting treatment guidelines.
Reducing undiagnosed HIV prevalence remains the greatest challenge in decreasing transmission in the UK. An HIV diagnosis reduces the risk of onward transmission in three ways. Firstly, it enables regular CD4+ and viral load monitoring among the untreated population. This ensures that diagnosed patients requiring treatment for clinical and/or prevention purposes are identified promptly. Secondly, once started, treatment is highly effective at reducing viraemia to undetectable viral loads. Thirdly, an HIV diagnosis provides access to behaviour change counselling.
Almost half (47%; 2950/6280) of new HIV diagnoses reported in 2011 were made at a late stage of infection (CD4+ cell count <350 at diagnosis) . Consequently, around one in two diagnosed with HIV in 2011 had been living with undiagnosed infection for around 3–5 years. In 2011, late diagnoses were particularly high among heterosexual men (64%) and women (56%) compared to MSM (35%) . This is a consistent pattern to the estimated proportion of each population with detectable viraemia. Black African populations are most vulnerable population with 68% of men and 61% of women diagnosed late.
HIV treatment has undoubtedly had an enormous impact on HIV transmission. However, in the UK, the diagnosed but untreated HIV population is already well monitored, and therefore less infectious than the undiagnosed population. We believe that the WHO guidelines are likely to have limited public health impact. ‘Treatment as prevention’ must be combined with efforts to reduce undiagnosed HIV infection. MSM are most at risk of acquiring HIV in the UK and black African heterosexual men and women are most at risk of late HIV diagnosis due to migrations patterns. In order to reduce transmission within these populations, increased HIV testing and primary prevention efforts remain a public health priority.
Conflicts of interest
There are no conflicts of interest.
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