An analysis of HIV diagnoses and incidence in English gay and bisexual men by Dr Francesco Brizzi and colleagues from the Medical Research Council has found that new HIV infections fell by more than two-thirds between 2013 and 2018. If this trend continues, new HIV infections could become a rare event in the gay population, and there is a 40% chance that England could hit the World Health Organization (WHO)/UNAIDS target of only one HIV infection in 10,000 gay men per year by 2030. Given that the estimated HIV-negative gay male population of England is about 475,000, this would imply only 80 new cases of HIV per year.
The researchers provide a more detailed analysis of the data from the 2019 Public Health England HIV surveillance report, which aidsmap covered in January 2020.
Using a more sophisticated method to estimate the annual number of new infections in gay men, they were able to stratify the population by age. This analysis reveals that although HIV infections in gay men have fallen in all age groups, they have fallen more slowly in men over the age of 45, such that they now have higher rates of both new HIV infection and undiagnosed infection than 35-45 year olds.
The fact that older gay men are now the age group at highest risk of gonorrhoea and syphilis suggests that a generation who, in the 1990s, may have been very observant of safer sex have also seen a larger relative rise in their risk of HIV. This suggests that HIV and STI testing programmes targeted specifically at older gay men may be needed.
Brizzi and colleagues ascribe the fall in HIV infections – a pattern not seen in many comparable countries – to a very high rate of testing in at-risk gay men and, most of all, to the almost universal provision of antiretroviral therapy (ART) as soon as possible after diagnosis.
Because the estimated peak of HIV incidence happened in 2013 – a couple of years before evidence of this started to appear in the diagnosis figures – the researchers say that this is almost entirely due to the effects of testing and treatment ('treatment as prevention') and not to PrEP. There were only about 250 gay and bisexual men taking PrEP in the UK by the end of 2013, mainly in the PROUD study, while online purchases of PrEP only began in the autumn of 2015.
The fact that the number of PrEP users has now expanded nearly 100-fold raises the possibility that widespread PrEP usage could accelerate the fall in new HIV infections. This could make it more likely that we will hit the one-per-10,000 infection target by 2030.
Results in detail
True incidence – the proportion of a group who are infected in a time period, in this case one year – is hard to calculate in a chronic infection like HIV. This is because positive test results are a mix of people who were infected recently and people who have had it longer. An increase in testing may initially detect more recent infections, but if testing is frequent enough (and if enough people diagnosed are on ART) it may detect then so efficiently that the proportion of diagnoses that are of recent infections falls, and the proportion of infections that are chronic rises. For this reason, as testing increases, diagnoses may continue to increase even though the true rate of infections has started to decrease. This is what the researchers found.
They used a complex algorithm taking account of CD4 count at diagnosis, age when infected, and the testing rate in different age groups to work backwards from observed diagnoses to the likely date of infection. This was also able to calculate the number of people with HIV who were diagnosed at any time point, and could also be projected forward to estimate future trends.
This model found that HIV infections in gay men probably peaked in the first half of 2013. Annual incidence then was 0.593% or one infection per year in every 169 English gay/bisexual men. This declined to 0.375% by 2015 and then to 0.18% by 2018, or one infection per year in every 556 men.
This is in contrast to some other countries such as the US, where incidence in the gay/bisexual male population was 0.5% in 2016 and is still about the same.
In terms of numbers of infections, between 2013 and 2018 the annual total estimated by the model fell by 69%, from 2770 to 854.
If these trends are continuing – and the evidence suggests they are – the researchers’ model suggests that incidence could fall to 0.053% by 2023 and 0.017% – one infection per year in about 5700 gay/bisexual men – by 2030. Uncertainties in the forecast, especially if PrEP provides additional benefits, means that there is a 40% chance that incidence could even fall to the WHO’s target of one infection per 10,000.
The model also shows that the proportion of all English gay/bisexual gay men who had HIV but remained undiagnosed fell from 1.7% in the 2012-15 period to 0.74% by 2018, or down from one in 59 to one in 135. This decline means that there are less than half as many gay men around who are potentially infectious (given that over 95% of those diagnosed are virally suppressed). Since the number newly infected each year is smaller than the number diagnosed, this proportion should continue to shrink.
As mentioned above, annual incidence in older gay men declined less steeply than in younger. Between 2013 and 2018, estimated infections in the 25 to 34-year-old age group fell by about 75%, but in men over 45 by 50%, and the fall started later. Similarly the estimated number of undiagnosed men with HIV fell by 46% overall but only 30% in men over 45.
How did we achieve this?
Because the decline in annual incidence started in 2013 when few men were taking PrEP, the remarkable decline in infections appears largely to be due to treatment as prevention, or what is often called 'U=U' (undetectable = untransmittable) when applied to individuals. Two factors made all the difference.
The first was a big increase in the number and frequency of HIV tests. The number of HIV tests in gay men at STI clinics nearly tripled from 60,000 in 2010 to 160,000 in 2018, and the average number of times gay men tested in a year increased from 1.4 to 1.8, thanks partly to a recommendation in 2012 that gay men at risk of HIV should test every three months rather than every six months.
“The lesson for other high-income countries is that amplified testing and treatment as prevention have controlled the HIV epidemic in England."
Probably even more crucial was the widespread adoption of immediate ART on diagnosis. In the first decade of this century treatment was not recommended until the CD4 count fell below 200 and as a result the proportion of people who had started treatment within six month of diagnosis stayed at around 30-35%. The CD4 threshold was changed to below 350 cells in 2008 and treatment for all was recommended in 2015. In 2018, 91% of diagnosed gay men started treatment within six months, with an average post-diagnosis wait of only 2-3 weeks.
Older gay men already tended to be treated earlier because they had often had HIV for longer and had lower CD4 counts, so there was less room for improvement.
However, part of the reason diagnoses and incidence have not fallen as fast in men over 45 is because, relatively speaking, the proportion who had sex that risked HIV may have increased more. Gonorrhoea diagnoses in men over 45 rose 15-fold between 2010 and 2015, as opposed to tenfold in other age groups. Syphilis increased about fivefold rather than threefold.
During the period surveyed, relatively small numbers of gay men were on PrEP, so we are yet to see whether this will lead to a further decline in new HIV infections, as it appears to have done in Scotland. By 2017, 15,000 people in the UK were taking PrEP and we may see an additional effect on infections from this time onward.
Brizzi and colleagues conclude: “The lesson for other high-income countries from experience in England is that amplified testing and treatment as prevention have controlled the HIV epidemic in England at the country level.
“With additional large-scale implementation of PrEP, elimination of HIV transmission is likely to be within reach by 2030.”
Brizzi F et al. Tracking elimination of HIV transmission in men who have sex with men in England: a modelling study. The Lancet HIV, early online publication, 9 June 2021 (open access).