Viral load is the amount of virus in a specific sample amount of blood. For people with HIV, a measure of viral load combined with a measure of immune cells in the blood are used to determine when to start or change treatment for HIV infection. When a viral load is so low that it can’t be measured, it is called ‘undetectable’. Some people call this ‘zero viral load’, but the virus is still present.

In 2008, a controversial statement from the Swiss Federal AIDS Commission announced a consensus among the country’s HIV/AIDS experts about people with an undetectable HIV viral load. They concluded, based on several studies, that heterosexual people with HIV who have an undetectable HIV viral load for six months cannot pass on the virus through sex if they stick to their antiretroviral regimen and do not have any other sexually transmitted infections. Many experts and community groups did not agree with this statement.

This “Swiss statement” was intended to inform counsellors and other service providers who work with people living with HIV, especially those in serodiscordant relationships (where one partner is HIV-positive and the other is not). Many people living with HIV and their partners welcomed the statement, because it gave them a new tool to help manage their risk of transmission.

Many guys who have heard of the Swiss statement wonder if it applies to them, and whether they need to use a condom if they or their partners have an undetectable HIV viral load.

It’s up to you what level of risk you are comfortable with. Here are the facts:

• The Swiss experts only looked at heterosexual couples. No similar research has been published on men who have sex with men or anal sex.
• In the studies cited by the Swiss experts, there was no statistically significant difference in the transmission of HIV comparing HIV-positive individuals on therapy to individuals not on therapy. Two more recent studies (one in China and one in Uganda) continue to bear this out and found no difference in HIV transmission comparing HIV-positive individuals on therapy and those not on therapy.
• Other research published since the Swiss study has shown that there can be detectable amounts of HIV in semen or vaginal fluids even in people who have an undetectable viral load in their blood.
• Viral load can fluctuate for a variety of reasons, such as missing treatment doses or getting another infection. An ‘undetectable’ measurement is only valid on the day it is measured.
• In a recent research study on 102 gay and bi guys who were recently diagnosed HIV-positive, nine of them were relying on the undetectable viral load of their HIV-positive partner. This study doesn’t tell us enough about the overall effectiveness of this strategy, since it doesn’t include men who rely on undetectable viral load and continue to test negative.
• Undetectable viral load does not mean the virus is not present. Viral load testing can only detect more than 40 copies of virus or more per cubic millilitre of blood.
• Sexually transmitted infections, vaccines, and some drugs can increase viral load.

The Swiss Federal AIDS Commission statement

commission fédérale pour les problems liés au sida commission clinique et thérapie vih de fédéral la santé publique Bulletin des médecins suisses.

Serodiscordant relationships [pamphlet] / Les relations sérodiscordantes [dépliant]

The ACT statement on Viral Load