1 Immune system and CD4 count

1.11 Different stages of infection

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Stages of HIV infection are described in slightly different ways by different organisations like the World Health Organisation (WHO) and the US medical system, etc. Now that there are effective treatments, these stages are less important.

• The WHO stages use symptoms only and do not use test results.
• The US-based Center for Disease Control (CDC) categories use both symptoms and test results.

WHO classification

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.

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 itself a definition of an AIDS diagnosis.

Before there were effective treatments, people were frequently categorised based on how ill they were and their life expectancy. This system is used less now where treatment is available.

Before HIV treatment, people did not generally get better, so that the progression through stages A, B and C was a 'one-way' direction.

AIDS-defining infections for CDC clinical categories.

Table: CDC categories of HIV infection

CD4 count	A No symptoms inc. primary infection	B* Symptoms (if not A or C)	C** AIDS-defining infections
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, many active lymphoma, pulmonary TB, KS, MAI, PCP, weight loss more than 10%, bacterial pneumonia, PML, toxoplasmosis.