Viral load is the amount of HIV present in different body fluids and tissues. A test to measure viral load in blood plasma has been available in Canada since 1997.
People with a high viral load are considered more “infectious” than those with a low viral load. When HIV is left untreated, viral load will be very high shortly after infection during the “seroconversion” period, before the body has begun to make antibodies to HIV. After seroconversion, the viral load decreases. Gradually, as the disease progresses, viral load will increase (at different rates depending on the individual). In the later stages of HIV disease, viral load is very high. Other factors (e.g. nutrition, STIs, local infections, other illnesses) may also affect a person’s viral load.
The use of combination antiretroviral drugs (combination therapy) can reduce HIV viral load, sometimes below the limit of detection of the available viral load tests. In Quebec, the sensitivity of each test is up to 50 copies per millilitre. However, a viral load result that reads “undetectable” does not mean that no HIV is present in the body; merely that it is reduced substantially.
Studies have shown that when viral load is reduced in blood it may also be reduced in semen, vaginal fluid, anorectal mucosa and breast milk. This may reduce the risk of HIV transmission, but it does not eliminate the risk. A person’s viral load level may fluctuate considerably between tests and several factors may affect each individual’s viral load. To ensure that no transmission of the virus takes place, we recommend that protection always be used.