At set-point, virus production and clearance are believed to reach a balance, creating a stable level of HIV RNA (viral load) in the blood.

No symptoms are shown during set-point. However, the higher the viral load at set-point, the faster HIV is expected to progress to AIDS, and the rate of transmission increases.

The level of HIV RNA at set-point can be lowered if antiretroviral therapy is started soon after infection.

The researchers of the study selected 906 patients from the Netherlands who had received no prior therapy, and who had measured their HIV-1 RNA concentrations at least once between 9 to 27 months after seroconversion.

Seroconversion is when the development of detectable HIV antibodies occurs.

Measurement of HIV-1 RNA concentration between 9 to 27 months ensures that virus concentration will be measured at set-point, when the viral loads are stable.

Consequently, this reduces the chance of biased results.

After selecting the patients, the researchers measured changes in HIV-1 RNA levels and CD4 counts at viral set-point. CD4 cells protect the body against infection.

However, HIV attacks and kills CD4 cells. Since the virus progressively kills these cells, they are measured to determine the severity of HIV.

In patients who seroconverted between 1984 and 1985, the mean of the first measured HIV-1 RNA concentration was 4.30 log10 copies/ml (this unit of measurement indicates the copies of HIV-1 RNA per milliliter of blood using a logarithmic scale).

HIV-1 RNA levels were similar for patients who seroconverted between 1996 and 2002 (4.27 log10 copies/ml).

However, patients who seroconverted between 2003 and 2007 had an average HIV-1 RNA level of 4.59 log10 copies/ml, representing an increase over the last decade.

Complementing this increase in HIV-1 RNA concentration was a decrease in CD4 cell count at viral set-point.

For more information, please see the PLoS ONE Web site.