`Test and Treat` HIV Prevention
posted: 19/03/2010
Treating everyone to halt the HIV epidemic in the worst-affected countries is not the best way to end the global epidemic, say mathematical modelling experts at London’s Imperial College. We can make deep cuts in new infections across the globe without going as far as universal treatment and annual testing.
Recently the end of the global HIV epidemic is predicted if we start universal regular HIV testing and then treat everyone with HIV. The claim is that universal testing and treatment could virtually eliminate HIV epidemic in countries like South Africa within 20 years.
Imperial College's Infectious Disease Epidemiology group created computer models to look at exactly what might happen if the world did adopt a ‘test and treat’ all HIV prevention strategy.
Running the models revealed that sexual behaviour changes would make a big difference.
Best: Test every 4 years, and treat 80% of people
The researchers showed that treating 80% of those with CD4 counts below 350, and getting everyone to take an HIV test every four to five years, could be the most cost-efficient strategy for reducing new infections.
Computer models and the real world
The Imperial College computer model follows another attempt to work out how well testing and treating works as a means of HIV prevention, from the World Health Organisation (WHO). The earlier WHO model showed that new HIV infections could be eliminated by 2030 in countries like South Africa, if universal annual testing was introduced, and people who are diagnosed then immediately start treatment.
There’s been a lot of interest and debate – how sure can we be that treating most people would cut HIV in the highest prevalence countries? Would the computer predictions work in the real world?
Sexual behaviour makes a big difference
Imperial’s computer model of the epidemic is different from the WHO model. Imperial looked at how differences in people's sexual behaviour affects how well treatment and testing works. Imperial also looked at the effects of changing how often people are retested for HIV, and how starting treatments at different CD4 levels would affect the future pattern of the epidemic.
Imperial’s results broadly confirm the results of the WHO model. Testing and treatment in `hyper-endemic` countries would have a profound impact on new HIV infections.
However, the model showed that results would be highly dependent on the character of the local epidemic. If people with large numbers of sexual partners have sex with people who have very few partners, new infections would be reduced by 85%, but would not be eliminated.
If there is not much sexual contact between people at high-risk and those at low-risk, testing people every two years would be necessary to bring down new HIV infections by 90%.
But where there is much more sexual mixing, testing would need to be much more frequent; we might have to diagnose every person with HIV within one month of their infection to cut total transmissions by the same 90%.
95% cut in infections
New infections might be reduced by 95%, if 80% of the population were to be tested every three to four years, and started treatment at a CD4 count around 400.
Only in the worst situations, where new infections have failed to fall despite years of prevention efforts, would more frequent testing be cost-efficient. In the worst situations testing 80% of people every two to three years and starting treatment even earlier (above CD4 of 450) would give the best results.
Test and treat success varies
“It is likely that the `test and treat` approach is much better suited to some populations and poorly suited to others,” they conclude. “There are diminishing returns for increasing testing frequencies to once-per-year levels. Failing to achieve sufficiently high coverage levels or failing to test frequently enough could just lead to a dramatic spiralling of treatment costs.”
Reductions in incidence of 85% - 95% would take around 30 years to achieve, so in the short term, treatment costs would rise.
They speculate that targeting particular population groups or locations for testing, such as truck drivers or beer halls, might prove particularly effective. However targeting raises serious worries over the human rights risks in `test and treat` strategies.
Models and the Real World
In the latest issue (March 2010) of HIV Treatment Update, Gus Cairn’s lead article gives the example of San Francisco. Here 85.5% of people with HIV are diagnosed (in England it is far lower – only around 75% are diagnosed); 78% of these attend clinics; 90% of these take HIV treatment; of those taking HIV treatment, 72% have an undetectable viral load.
As Gus says: ‘Do the sums: even with such high testing and coverage rates, only 43% of San Franciscans with HIV have an undetectable viral load. Treatment as prevention will need to be truly universal to work.’
Source with reference
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