Summary
HIV viral load is the amount of HIV (or number of virus) in the bodily fluids of someone living with HIV. It is measured in the blood as part of routine clinical care. A higher viral load is associated with a higher risk of HIV transmission. Research shows that successful HIV treatment can reduce the viral load to “undetectable” levels and this can significantly reduce the risk of HIV transmission. However, HIV transmission may be possible when the viral load is undetectable because there is still virus present in the blood and other bodily fluids. The risk of HIV transmission for someone taking antiretroviral treatment may increase if sexually transmitted infections (STIs) are present, doses of medications are missed, or drug resistance develops. This risk may also be higher for receptive anal sex (where the HIV-negative partner is the receptive partner, or bottom) than for other types of sex.