366
U N I T 4
Infection and Immunity
The primary stage is followed by a latent period (stage 2)
during which the person has no signs or symptoms of
illness. The median time of the latent period is about
10 years. During this time, the CD4
+
T-cell count falls
gradually from the normal range of 800 to 1000 cells/
μ
L to 200 to 499 cells/
μ
L (14% to 28%). More recent
data suggest that the CD4
+
T-cell decline may not fall
in an even slope based on HIV RNA levels, and factors
related to the variability in the decline in CD4
+
T cells
are under investigation.
59
Lymphadenopathy (i.e., swol-
len lymph nodes) for more than 3 months in at least two
locations (not including the groin) develops in some per-
sons with HIV infection during this phase. The lymph
nodes may be sore or visible externally.
Stage 3 (overt AIDS) occurs when a person has a CD4
+
T-cell count of less than 200 cells/
μ
L (<14%) or an AIDS-
defining illness.
60
Without antiretroviral therapy, this
phase can lead to death within 2 to 3 years. The risk of
opportunistic infections and death increases significantly
when the CD4
+
T-cell count falls below 200 cells/
μ
L.
The clinical course of HIV varies from person to
person. In the absence of treatment, most people with
HIV infection progress to AIDS after 7 to 10 years.
2,60
These people are the
chronic
or
typical progressors.
Another 10% to 20% are
rapid progressors
who
develop AIDS within 2 to 3 years after primary infec-
tion. The final 5% to 15% are
long-term nonprogres-
sors,
who remain asymptomatic for 10 years or more
after seroconversion, with stable CD4
+
T-cell counts
and low plasma HIV RNA levels. A subset of these
long-term nonprogressors, called
elite controllers,
have plasma HIV RNA levels that are below the level
of detection. Studies of these individuals have helped
to identify host and viral factors that influence disease
progression.
2
One factor found to be important in elite
control is a mutation in the genes coding for CCR5, a
coreceptor used for HIV entry. Mutations in both genes
result in CD4
+
cells with a defective CCR5, thereby
preventing HIV entry into those cells. Research in this
area is ongoing.
2–4 weeks
Acute clinical syndrome
8–10 years
Latency
2–3 years
Overt AIDS
HIV-1
exposure
viral load
CD4
T-lymphocyte
count
+
Levels of viral
load and CD4
immune
response
+
FIGURE 16-9.
Viral load and CD4
+
cell count during the phases of HIV infection. AIDS, acquired
immunodeficiency syndrome; HIV, human immunodeficiency virus.
TABLE 16-2
The Revised CDC Classification System for Human ImmunodeficiencyVirus (HIV)
Infection in Adults and Adolescents Aged 13Years.
*
CD4
+
T-cell Count Cells/μL
(CD4
+
T-cell Percentage)
Stage
AIDS-defining Conditions (ADC)
Stage 1
≥
500 (29%)
No ADC
Stage 2
200–499 (14%–28%)
No ADC
Stage 3
<200 (<14%)
No documented ADC
Stage undetermined
No information
No information
*A confirmed case meets the laboratory diagnosis of HIV infection and one of the four stages. Although
cases with no information on AIDS-defining characteristics can be classified as stage unknown, every effort
should be made to obtain CD4
+
T-cell counts and percentages and the presence of AIDS-defining conditions
at the time of diagnosis.
Developed from Schneider E, Whitmore S, Glynn KM, et al., for the Centers for Disease Control and
Prevention (CDC). Revised case definitions for HIV infections among adults, adolescents, and children aged
<18 months and for children aged 18 months to <13 years—United States, 2008. MMWR Recomm Rep.
2008;57(RR-10):1–12.
