The more people take anti-HIV treatment, and the sooner they start, the more new infections are averted

Michael Carter
Published: 11 June 2008

Expanded use of antiretroviral therapy - accompanied by good adherence - has the potential to significantly reduce the spread of HIV, according to the results of a mathematical model developed by Canadian researchers and published in the July 1st edition of the Journal of Infectious Diseases.

They calculated that over two-thirds of all projected new HIV infections by 2030 in British Columbia would be averted if all individuals eligible for antiretroviral therapy started such treatment when their CD4 cell count was in the region of 350 cells/mm3 - the current recommended threshold for initiating anti-HIV treatment.

There is unlikely to be an effective vaccine for HIV for some time and current prevention work is only partially effective. Treatment with anti-HIV drugs can mean a longer, healthier life for HIV-positive individuals, and access to antiretroviral therapy is expanding across the globe.

As well as having benefits for the individual patients, antiretroviral therapy may also have public health benefit. Treatment with anti-HIV drugs lowers the amount of HIV in the body, significantly reducing the infectiousness of HIV-infected individuals. In a recent controversial statement, leading HIV physicians in Switzerland suggested that patients taking anti-HIV treatment who have had an undetectable viral load in their blood for at least six months, who take their treatment properly, and who do not have a sexually transmitted infection, should not be considered infectious to their sex partners.

Even in countries with universal access to antiretroviral therapy, large numbers of patients do not start treatment, even when their CD4 cell count suggests that they are at risk of developing an AIDS-defining illness. Very high levels of adherence to anti-HIV treatment are needed to obtain the best results and to avoid the development of drug resistance, but many patients find this difficult to achieve and maintain.

Investigators in the Canadian province of British Columbia, which has universal free access to antiretroviral therapy, developed a series of mathematical models to assess how increasing access to antiretroviral therapy, the early initiation of anti-HIV treatment, and improved levels of adherence would affect the spread of HIV in the province by 2030.

At the moment only 50% of HIV-positive individuals in British Columbia start antiretroviral therapy before their CD4 cell count falls to below 200 cells/mm3, and patients on treatment take approximately 78% of their doses – well below the 95% target and at the level which involves the greatest risk for the development of drug resistant virus. The investigators calculated that this level of treatment coverage and adherence would lead to a modest increase in the annual number of new HIV infections every year – from 421 in 2006 to 462 in 2030.

They then calculated the potential impact of more patients starting anti-HIV treatment before their CD4 cell count fell to the 200 cells/mm3 threshold. Their calculations showed that if 75% of eligible patients had started treatment by this stage it would yield a 37% reduction in the total number of new HIV infections, and if 100% of patients had started treatment by the time before they reached a CD4 cell count of 200 cells/mm3, then 62% of onward transmissions would be averted.

HIV treatment guidelines around the world now recommend that patients should start antiretroviral therapy when their CD4 cell count is in the region of 350 cells/mm3 and the investigators included this earlier initiation of therapy into their models.

Once again, they found that the current coverage rate of 50%, accompanied by 78% adherence would mean a modest increase in the number of annual HIV infections.

But they found that greater coverage of anti-HIV treatment would result in substantial reductions in the number of new HIV infections. Their calculations showed that if 75% of patients started treatment when their CD4 cell count was 350 cells/mm3, then 40% of the projected new infections by 2030 would be averted, and this increased to 67% of anticipated infections if all patients started treatment when their CD4 cell count was around 350 cells/mm3. Increasing patient adherence would further modestly increase the number of averted infections.

Faster expansion of anti-HIV treatment would result in faster decreases in the numbers of new infections, according to the investigators' model. Furthermore, immediate expansion of access to anti-HIV treatment would save a total of Canadian $95 million, or Canadian $368,000 per patient.

“Our results indicate that higher HAART coverage consistently leads to a decrease in the number of individuals testing newly positive for HIV”, write the investigators. They conclude, “expansion of HAART coverage should lead to a substantial reduction of the growth of the HIV epidemic and related direct treatment costs. Our model supports a powerful and as-of-yet little appreciated additive preventative value for expanding HAART coverage.”

Reference

Lima VD et al. Expanded access to highly active antiretroviral therapy: a potentially powerful strategy to curb the growth of the HIV epidemic. J Infect Dis 198 (online edition), 2008.