Viral Load and Transmission


viral_load_and_transmission_smFor someone who is HIV positive and in, or considering a sexual relationship with a positive person, the risk of HIV transmission is an important issue. In the summer of 2011, results from the HPTN 045 study were released stating that with an undetectable viral load, the risk of HIV transmission was decreased by up to 96%. Based on this study, and a few much smaller studies at the time, it seemed that the scarlet letter that was placed on HIV positive people as being infectious was lifted for the lucky ones who were able to achieve an undetectable viral load. However, many in the HIV professional field as well as HIV activists and advocates were reluctant to discuss the issue of a decrease in risk of transmission based on available research.

In the two years that followed HPTN 045 it’s become apparent that it is not as simple as an undetectable viral load equates to being non-infectious while a detectable viral load equals being infectious. Research subsequent to HPTN 045 has taught us several things: whereas an undetectable viral load DOES decrease the risk of transmitting HIV to negligible (near non-existent) levels, other factors then increase the risk back upward. We know that sexually transmitted diseases increase the risk but it is not clear by how much. We also know that anal sex increases the level of risk in comparison to vaginal sex. The risk of transmission is also greater when the positive person is the inserting partner.

Another important factor when weighing risk is that an undetectable viral load is a snap shot of how much virus was in the blood at the time the test was taken. Since this number can fluctuate, the amount may have increased or decreased since that time. It can be different from month to month, week to week, day to day and even hour to hour. So a person may have been undetectable at the time of their last test but may not be shortly after. Viral load measurements are taken from the blood (peripheral). Research has determined that peripheral viral load may differ from HIV viral load found in semen, vaginal or anal fluids. Thus, your viral load may be undetectable in your blood but may be higher in other body fluids that can effect transmission.

In summary, additional factors can play a role in the level of transmission in the presence of an undetectable viral load.

  • Sexually transmitted diseases
  • Fluctuations in viral load from time of testing to sexual exposure
  • Differences in peripheral viral load from viral load in semen, vaginal or anal fluids
  • Type of sex – anal versus vaginal
  • Role or position as in being the inserting partner or the receiving partner.
Written by Jeannie Wraight
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