I have three questions: (1) Can an HIV patient transmit the virus when her viral load is undetectable -- whether to a partner or to her baby? (2) What's the explanation and implications of a CD4 cell count of about 170, with an undetectable viral load? (3) What advice is there for an HIV patient who still hopes to be a wife and a mother?

G.C.

First let me give some background. The viral load is the amount of virus particles per milliliter of blood. This has been shown to be an excellent predictor of the rate of progression to AIDS and death. On average, it takes about 10 years for a patient to go from infection to death. This correlates with an average viral load of about 50,000. Patients who have a higher load will likely progress faster than that. Those who have a lower load progress more slowly. There are some who have an undetectable viral load (a level that is too low for our tests to measure). Some of these patients have not developed any sign of the disease after more than 15 years.

The CD4 cell is the immune cell most affected by HIV. A normal CD4 count is about 1,000. When it drops below 200, the patient is at risk of many AIDS-related infections. If a patient has a high viral load, then he or she is at high risk of developing a low CD4 count and thus a serious infection in the near future.

Now for your questions:

1. The higher a patient's viral load, the more likely it is for the person to transmit the virus. This has been shown to be true for pregnant mothers transmitting HIV to the fetus. It is probably true for sexual partners and for needlestick injuries, but the data are not quite as secure as for transmission from mother to baby. However, there is no viral load that gives absolute safety from transmission. Infection has occurred when the viral load was undetectable.
   
2. A person who has a CD4 count of about 170 is at some risk of developing AIDS-related infections such as pneumocystis pneumonia. The person is at low risk of developing certain other infections, including CMV and toxoplasmosis. Because the viral load is undetectable, the CD4 count may not fall, and it may actually rise, at least in the short term. Usually, numbers such as these are seen in patients who are on therapy for HIV. The viral load was probably detectable for some time, and the CD4 count fell. Then treatment began, the viral load dropped, and the CD4 count rose. There is some concern that these new CD4 cells are not as effective in fighting infection as the original cells, but they have some effect. Patients live longer and develop fewer infections when their CD4 count rises.
   
3. Your last question is by far the most difficult to answer. People who are infected with HIV certainly do get married. It is obviously a difficult situation, as there is worry about the future, concern about transmission to the unaffected partner and fear for any children. My advice is to stress communication with the potential mate. He has to know exactly what he can expect. Bring him to your doctor if he agrees to go. This may allay some fears and help him understand what the future may hold.
   

If a woman is under treatment for HIV during pregnancy and the baby is treated after birth, the risk of transmission to the baby can be less than 5 percent. Many people consider this low enough to justify trying to have a baby. The other obvious concern is that there is a good chance that the mother will have a shortened life. Any potential parent with a life-threatening disease must take that into consideration.