1.11 Different stages of HIV infection
Stages of HIV infection used to be described differently by the World Health Organisation (WHO) and the US medical system.
The different stages are generally less important because of HIV treatment (ART) is now so effective and widely available.
- WHO recently changed to using a CD4 test results. They define advanced HIV disease (AHD) as having a CD4 count less than 200.
- Before this, WHO stages of infection were defined using symptoms only and not test results.
- The US Center for Disease Control (CDC) categories use both symptoms and test results.
Current WHO classification
Now that CD4 tests are more widely available globally, WHO mainly just refers to HIV infection and advanced HIV infection.
- HIV infection is any CD4 count above 200.
- Advanced HIV disease (AHD) is any CD4 count less than 200.
Old WHO classification (no longer used)
The old WHO performance stages did not include CD4 counts. They used a person’s health (performance stage) plus signs of illness (symptoms):
- Performance stage 1: no symptoms (asymptomatic), normal activity.
- Performance stage 2: symptoms, but nearly fully ambulatory.
- Performance stage 3: in bed more than normal but less than half of normal daytime during the previous month.
- Performance stage 4: in bed more than half of normal daytime during previous month.
These WHO clinical stages increased with the severity of opportunistic infections.
US CDC categories
The US classify HIV in one of five infection stages (0, 1, 2, 3, or unknown):
Stage 0 is early infection (estimated as within 6 months of HIV diagnosis), progressing to stage 3 for advance HIV infection (CD4 <200, previously AIDS).
US clinical categories, use number 1, 2 and 3.
This uses the same table for children and adults and is qualified by the CD4 count and CD4 percentage.
In the US (but not Europe) a CD4 count under 200 cells/mm3 is a definition of advanced HIV. This used to be called an AIDS diagnosis.
Before effective ART, people were frequently categorised based on how ill they were and their life expectancy. In 2023, this system is less relevant.
Before ART, people did not generally get better, so that the progression through stages A, B and C was a one-way direction.
Revised Surveillance Case Definition for HIV Infection — United States, (April 2014)
www.cdc.gov/mmwr/pdf/rr/rr6303.pdf ( 2014, PDF)
Table: CDC stages* of HIV infection (2014) |
||||||
|---|---|---|---|---|---|---|
|
Stage |
Age (when CD4 test was taken) |
|||||
|
<1 yr |
1–5 yrs |
≥6 yrs |
||||
|
cells/mm3 |
% |
cells/mm3 |
% |
cells/mm3 |
% |
|
|
1 |
≥1,500 |
≥34 |
≥1,000 |
≥30 |
≥500 |
≥26 |
|
2 |
750–1,499 |
26–33 |
500–999 |
22–29 |
200–499 |
14–25 |
|
3 |
<750 |
<26 |
<500 |
<22 |
<200 |
<14 |
* The stage is based primarily on the absolute CD4 count; this is more important than the CD4 percentage.
There are three situations in which the stage is not based on this table.
- If the criteria for stage 0 are met, the stage is 0 regardless of criteria for other stages (CD4 results and opportunistic illnesses).
- If the criteria for stage 0 are not met and a stage-3-defining opportunistic illness has been diagnosed (See Appendix in US document), then the stage is 3 regardless of CD4 test results.
- If the criteria for stage 0 are not met and information on the above criteria for other stages is missing, then the stage is classified as unknown.
Last updated: 1 January 2023.