Clinical Overview of HIV Disease
Section 5: Classification of HIV Disease
HIV damages the immune system, leaving the infected person vulnerable to a
variety of infections (called "opportunistic" infections to indicate that they
arise in the setting of immune impairment). 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. Such individuals are unlikely to require
treatment. CD4 counts <350 cells/µL indicate that some impairment of immune
function is present, and should prompt consideration of ART. CD4 counts <200
cells/µL indicate imminent risk of serious OIs or other complications of HIV
disease, and prompt treatment is recommended.( 38 )
Untreated HIV disease is chronic and progressive. Primary HIV infection, often
marked by a mononucleosis-like acute viral syndrome, is followed by a period of
clinical latency typically lasting several years, during which high levels of
viral replication and CD4 cell turnover lead to progressive immune dysfunction,
eventually resulting in clinical disease progression. The distinction between
"HIV infection" and "AIDS" is important, as it has clinical and prognostic
implications, as well as utility in research.
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 (see
Table 1 ). 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 (see
Table
2 ).( 105 )
The World Health Organization has developed a clinical staging system for HIV
infection (see Table 3 ).( 106 ) This system relies more heavily on clinical
rather than laboratory evaluation, and has been used widely in
resource-constrained areas where laboratory testing is not widely available.
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