I have heard that some people who get infected with hiv, never develop aids, and stay healthy. Is this true? What is the percentage? What are the factors involved in this non-progression to aids? Thanks

There are many different definitions of "long-term non-progressors." One includes patients who have normal and stable CD4 cell counts for over seven years without antiretroviral therapy. Another includes patients with HIV infection for 13 years or more who are asymptomatic, have CD4 counts over 600, and no decrease in CD4 in over 5 years without antiretroviral therapy. Another type of long-term non-progressor is the patient with low, stable CD4 count (less than 200) for 5 years or more without an AIDS-related illnesses.

Of course, the proportion of HIV-infected individuals who are long-term non-progressors depends on which definition you use. But in one large cohort study of gay men with HIV infection, it was suggested that 13% will remain asymptomatic for over 20 years. Of course we have no way of knowing what the long-term prognosis for such people will be, since AIDS hasn't been around long enough.

We don't know yet why some people progress rapidly and others don't progress at all. Genetic factors almost certainly play an important role, but we're not at the point yet where we can predict in advance who will be a long-term non-progressor.