D differentiate between the difference in the

d. Differentiate between the difference in the diagnoses of HIV Infection and AIDS and
describe the clinical implications.
The effect of HIV on the immune system is monitored by measuring the CD4 (helper)
lymphocyte count in the blood. A normal CD4 count (between approximately 600 and 1,200
cells/µL) indicates that the immune system has not undergone sufficient damage to put the
individual at risk for opportunistic illness. The U.S. Centers for Disease Control and Prevention
(CDC) definition of AIDS, initially published in 1986 and revised in 1993, is based on certain
clinical conditions, infections, and malignancies associated with HIV infection. Additionally, AIDS
may be defined by a CD4 count of <200 cells/µL or <14% of all lymphocytes, even in the
absence of the listed conditions.
Primary HIV infection is defined as the time period from initial infection with HIV to the
development of an antibody response detectable by standard tests. During primary HIV
infection, HIV-specific CD8 cells undergo a marked clonal expansion and express high levels of
activation markers such as CD38 and human leukocyte antigen. CD4 counts and CD4 function
may decline during primary HIV infection, occasionally to levels that allow OIs to develop.
Absolute CD4 count often rebounds after the primary infection, but may not return to a normal
baseline.
After the period of acute HIV infection--during which CD4 counts and viral load change
dramatically--a relative equilibrium between viral replication and the host immune response is
reached, and individuals may have little or no clinical manifestations of HIV infection. This time
between initial infection and the development of AIDS may be long, averaging 10 years, even in
the absence of treatment. Despite the relative clinical latency of this stage of HIV infection, viral
replication and CD4 cell turnover remain active, with millions of CD4 cells and billions of virions
produced and destroyed each day. On average, CD4 counts will drop by 50-90 cells/µL per year
in asymptomatic individuals, usually with an acceleration of this rate over time. The rate of
progression of infection may vary considerably. In adults, progression from infection to clinical
AIDS is rare in the first 2 years of infection; however, reports describe rapid disease progression
in infants infected by blood transfusion.
According to CDC criteria AIDS is defined by either diagnosis of one of the AIDS-defining
conditions, or by measurement of CD4 levels <200 cells/µL. Progression to AIDS from time of
infection occurs, on average, 2 years earlier when defined by laboratory criteria (CD4 levels
<200 cells/µL) compared to clinical criteria (development of an opportunistic illness). Survival
time from the development of AIDS varies according to the AIDS-defining event. In the
Multicenter Hemophilia Cohort Study, median survival after a single AIDS-defining condition
ranged from 3 to 51 months for the 10 most common conditions. The mean survival time after
diagnosis of AIDS in the United States prior to the availability of antiretroviral treatment was 10-
12 months.