HIV ESTABLISHED INFECTION

Regardless of whether the syndrome of acute HIV infection is recognized or not, after the HIV-specific immunological response begins to control the intensity of viremia, a so-called “viral set point” is established which varies by individual. With exceedingly rare exceptions, the immunological response to HIV does not eliminate infection, but rather establishes steady state between viral replication and elimination. A variable level of viremia is attained that can be measured via quantification of the number of copies of HIV RNA present in blood (viral load). Although the viral load within the first 120 days of HIV infection is not of prognostic value, most patients establish a relatively stable viral load after recovering from acute infection, and this viral set point is highly predictive of the rate of future progression of illness. In the case of a high viral load set point (i.e., values ranging up from 40000 copies/mm3), more rapid decline in CD4 cell counts and more rapid occurrence of Clinical Class B and C conditions will occur. Some patients have low viral load set points (below 500 copies/mm3), which indicates a better prognosis; no evidence of progression (CD4 cell depletion or HIV diseases) is seen for long periods of time in a small subset of patients (see section on long-term progression, below). The viral set point is likely influenced by several factors such as presence of other infections at the time of HIV exposure, genetic characteristics (particularly the type of HIV binding receptors present on lymphocytes), viral characteristics, age, and perhaps sex (see below) (Kahn, 1998).
During the period of clinical stability, acute illnesses and other events that can stimulate the immune system, such as influenza, Herpes simplex outbreaks, tuberculosis, and even routine vaccinations, have resulted in 10–1000-fold increases in viral load; these increases are transient and most often resolve within 2 months (Stanley, 1996). Thus, determination of viral load for prognostic purposes should not be done during or shortly after an acute illness.