Viral load is usually reported as the number of copies per milliliter of blood, where copies refers to the viral genome.
It is important for patients to know that having an "undetectable" viral load does not mean that they have been cured. It just means that the level of virus circulating in their blood has fallen below the level detectable by the test. The threshold beneath which an infection is "undetectable" is strongly dependent on the type of test used. As tests improve, they will continue to be able to detect lower and lower levels of virus in a person's blood.
Effective medications for viral illnesses such as HIV will lower a person's viral load for some amount of time. Depending on individual, virus, and treatment factors, a patient's viral load may remain undetectable for months or even years at a time before rising once again to detectable levels.
