Andrew Phillips then shifted his attention to predictions of the potential impact of changes to treatment guidelines, or the uptake of HIV testing, or both. His estimations are based on mathematical models which take into account multiple sources of data on the UK epidemic and varying assumptions about sexual and testing behaviour.
In terms of policy changes, he considered the impact of immediately recommending HIV treatment after diagnosis with HIV, rather than the current treatment guideline of starting treatment with a CD4 cell count of 350 cells/mm3. The application of this policy should depend on the outcome of the START randomised trial, examining the impact of early treatment on the health of the person living with HIV.
He also considered the possibility of changes to HIV testing, involving both an increase in the frequency of testing and a reduction in the number of men who have never tested. At present, approximately 40% of men are diagnosed within a year of acquiring their infection, but Phillips modelled the impact of two possible scenarios:
- A scale-up of testing, so that 60% are diagnosed within a year of infection.
- A larger scale-up, so that 90% are diagnosed within a year.
He did not know how such changes in testing behaviour could be achieved, but did say that they were "highly ambitious" and would likely require substantial investment.
The model forecast new infections up to the year 2030. It predicted that if there was no change in treatment policy or in testing, over 3000 men who have sex with men would acquire HIV during the year 2030. However, there is potential to reduce the number of infections through policy changes:
- Immediate treatment could reduce infections by 32%.
- A scale-up of testing could also reduce infections by 32%.
- A larger scale-up of testing could reduce infections by 54%.
- Immediate treatment and a scale-up of testing could reduce infections by 64%.
- Immediate treatment and a large scale-up of testing could reduce infections by 80%.
In the latter scenario, around 600 gay and other men who have sex with men would acquire HIV in 2030.
Preliminary analysis suggests that this scenario would be highly cost-effective. Although many more people would be taking HIV treatment in the first few years, the numbers on treatment would be falling by 2030 as fewer men acquire HIV.
Phillips noted a number of factors which could influence these outcomes. If retention in care and adherence deteriorated, so that 15% fewer men with HIV had an undetectable viral load, there would be around 1000 more infections each year.
Changes in sexual behaviour could also have an impact – a decrease in condom use is possible as the impact of treatment on transmission becomes better known. However, the effect of this would vary in the different scenarios.
If testing and treatment policy does not change, a relatively small increase of 10% more men having sex without a condom each year would result in a massive increase in infections – up to around 6000 in the year 2030.
In the scenario of immediate treatment and a large scale-up of testing, there would be a smaller pool of men with infectious HIV, so the impact of sexual behaviour change would be lesser. A 10% increase in sex without a condom would result in a few hundred more infections each year.
Phillips also suggested that in the most optimistic scenario, primary infection might have less impact on the epidemic than it does at present. He said that the effective treatment of men who have chronic infection would help prevent outbreaks of primary infection occurring.