1.11 Different stages of infection
Stages of HIV infection are described differently by the World Health Organisation (WHO) and the US medical system. These stages are less important because of effective HIV treatment (ART).
- WHO stages use symptoms only and do not test results.
- The US Center for Disease Control (CDC) categories use both symptoms and test results.
The WHO performance stages do not include CD4 counts. These performance stages are described using a person’s ability to do thing (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.
WHO clinical stages increase with severity of opportunistic infections.
WHO classification system for HIV infection, 2007. (PDF download)
US CDC categories
Clinical categories are shown with the letters: A, B and C.
This is qualified by CD4 count, shown by numbers: 1, 2 or 3.
In the US (but not Europe) a CD4 count under 200 cells/mm3 is a definition of an AIDS diagnosis.
Before effective ART, people were frequently categorised based on how ill they were and their life expectancy. In 2015, this system is less relevant.
Before HIV treatment, people did not generally get better, so that the progression through stages A, B and C was a ‘one-way’ direction.
CDC revised clinical categories for classification (1993 revision)
Table: CDC categories of HIV infection
No symptoms inc. primary infection
Symptoms (if not A or C)
|1 = 500 or over||A1||B1||C1|
|2 = 200-499||A2||B2||C2|
|3 = less than 200||A3||B3||C3|
* Less serious or early symptoms include: candida (thrush) in the mouth, or vagina if not responding to treatment, fever (over 38.5 degrees C) or diarrhoea lasting over 1 month, cervical abnormalities or cancer, pelvic inflammatory disease (PID)
** AIDS defining infections include all the most serious infections including: oesophagal candida, CMV disease, active lymphoma, pulmonary TB, KS, MAI, PCP, weight loss more than 10%, bacterial pneumonia, PML, toxoplasmosis.
Last updated: 1 January 2021.