Viral load is a measure of the amount of HIV circulating in the blood. This is only two per cent of the total amount of HIV virus in the body. Nevertheless, recent studies have shown that viral load can be used to accurately predict how quickly a person will progress to AIDS. Some virus can be found in "reservoir sites", such as the lymph nodes and other body tissue.
From the moment a person is first infected with HIV the virus is active and replicates rapidly. Immediately after infection high levels of virus can be found in the blood, but after this period of acute infection, the amount of virus falls and can stay at a relatively low level for years.
In 1996 researchers showed that people with high viral loads soon after being infected with HIV developed AIDS much faster than those with low viral loads (1). A year later these results were confirmed in a larger study (2) which also showed that the higher the viral load the greater the rate of decline in CD4 count.
Researchers now believe that keeping viral load as low as possible for as long as possible can improve the outlook for people with HIV by delaying the onset of AIDS. Two studies have shown that reducing viral load is linked to a slower rate of disease progression (3,4). Regular tests of viral load are therefore recommended.
Tests for viral load can be used, in conjunction with other health factors, for a number of purposes:
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