I am the mother of six children, three of whom were born in 1978, 1980 and 1983. Because of an anemic condition, I was given blood following the deliveries. I was tested for HIV in 1993 and luckily I tested negative. I know that the disease can lie dormant for many years before symptoms begin manifesting themselves. Do I need to be retested? If so, how often?

W.G.

You describe a common misconception about HIV, the human immunodeficiency virus, which causes AIDS. After infection, a person often develops an acute, flu-like illness. This "acute retroviral syndrome" usually causes fever, sore throat and rash. The patient usually recovers uneventfully from this illness, and HIV is rarely suspected as the cause. For the next five to 10 years, on average, the virus replicates, slowly affecting the immune system. However, most people have no symptoms at all during this time. Some people have a misconception that the virus itself is dormant -- but it is not. It just takes years for the virus to finally take its toll on the immune system.

During this "latent" stage, even though the patient has no symptoms, HIV tests should still be positive. The HIV tests commonly employed are just as accurate whether or not the infected person has symptoms. Since you tested negative in 1993, it would be exceedingly unlikely that you became infected with HIV from any of your transfusions. If you had been, you would have almost certainly tested positive 10 years later. In addition, it is now 17 years after your last transfusion. More than 90 percent of people with HIV will have developed some symptoms after that length of time. I do not think that you need any more testing, unless you have engaged in risky behavior since 1993.

I would like to also clarify a few things regarding blood transfusion and the risk of HIV infection. Before April 1985, the United States did not test blood for HIV. There was a relatively high risk from blood, especially in people who got pooled blood products, as was the norm for those with hemophilia. From 1980 to 1983, the risk of contracting HIV from a single unit of blood was as high as 1 in 100. In 1983, blood banks began asking donors specific questions, and people with a high risk of HIV were excluded from donating blood. Then, in 1985, testing of all blood products began, greatly lowering the risk.

Now, the United States tests all donated blood for both HIV-1 and the far less common HIV-2. In addition, a test is performed to help exclude the rare blood donor who may be in the brief "window period" between infection and testing positive. In all, the risk of HIV from a blood transfusion now is estimated to be 1 in about 500,000. The risk of acquiring any significant infection from a single blood transfusion is less than 1 in 30,000.