I have been HIV positive for almost nine years. I have had a decreasing CD4 on the average of every two years -- to just below 500. I have only had minor complications. My viral load was 15,000 then 11,000, and is now undetectable. What does this mean? Is this a good thing, or is the virus hiding in the central nervous system? If the virus is hiding, would it still be detectable in the viral load?

James

HIV, the virus that causes AIDS, is present in different amounts in different people. The virus inhabits cells throughout the body: in the blood, the lymph nodes, the internal organs, and the cerebrospinal fluid (the fluid that bathes the brain and spinal cord). We routinely measure the amount of virus in the blood -- the viral load. Many studies have demonstrated that a long-term prognosis (predicted outcome) of someone infected with HIV depends mostly on the viral load. The higher the viral load, the faster a patient typically progresses to AIDS, an advanced stage of HIV infection.

When we talk about virus "hiding out" somewhere, we mean that the virus may not be detectable in the blood, but it is found in the lymph nodes or in the central nervous system (brain and spinal cord) and cerebrospinal fluid. Scientists have found that after intensive therapy with anti-HIV drugs, many patients have undetectable viral loads, meaning there is no detectable virus in the blood. However, if one examines the lymph nodes, one invariably finds viable viruses. This explains the fact that if drug therapy is discontinued in someone with no detectable virus in the blood, virus levels rebound.

The cerebrospinal fluid (CSF) also can also contain HIV, even when there is no detectable virus in the blood. It is unclear what this means in most patients, but in those with neurologic disorders associated with HIV, such as HIV dementia, the viral load in the CSF may be important. In at least some studies, lowering the CSF viral load with anti-HIV drugs was associated with neurologic improvement. In your case, I am not sure whether you are on treatment or not -- but if you are, and your viral load has fallen to undetectable levels, I think that you are doing okay. Perhaps your CD4 T-cell count (a measure of the key immune cells that HIV attacks) has leveled off and it will not decline further. If this is the case, and you are not experiencing dementia or other neurologic problems, I would not worry too much about the possibility of virus in the central nervous system. You do have virus hiding out in the lymph nodes, just like everyone else with HIV infection, so I would not want you to stop therapy.

If you are not on treatment, then it is unusual that your viral load has fallen to undetectable levels. In most patients with HIV infection, the viral load remains steady or rises unless they are taking anti-HIV drugs. Still, if you are not having neurologic problems, there is no real reason to be concerned about the CSF levels of virus. If you do have detectable virus in your CSF, it may be more likely that you develop HIV-related neurologic complications in the future, but there is not much data to support the routine measurement of the CSF viral load. If you already do have such complications, then it would be wise to treat you with medications that have been shown to penetrate into the CSF.