The following World Health Organization (WHO) definitions are designed for use in developing countries. They are based on clear clinical markers and do not require any of the diagnostic technology which is likely to be lacking in countries where such resources are limited.

Clinical stage 1

• Asymptomatic.

• Persistent generalized lymphadenopathy.

• Performance scale 1: asymptomatic, normal activity.

Clinical stage 2

• Weight loss: less than 10% of body weight.

• Minor mucocutaneous manifestations: seborrhoeic dermatitis, prurigo, fungal nail infections, recurrent oral ulcerations or angular cheilitis.

• Herpes zoster within the last five years.

• Recurrent upper respiratory tract infections, e.g. bacterial sinusitis.

• Performance scale 2: symptomatic, normal activity.

Clinical stage 3

• Weight loss: more than 10% of body weight.

• Unexplained chronic diarrhoea for more than one month.

• Unexplained prolonged fever, intermittent or constant, for more than one month.

• Oral candidiasis (thrush).

• Oral hairy leukoplakia.

• Pulmonary tuberculosis within the past year.

• Severe bacterial infections, e.g. pneumonia or pyomyositis.

• And/or performance scale 3: bedridden <50% of the day during the last month.

Clinical stage 4

• HIV wasting syndrome, as defined by the Centers for Disease Control and Prevention.

• Pneumocystis pneumonia.

• Toxoplasmosis of the brain.

• Cryptosporidiosis with diarrhoea for more than one month.

• Extrapulmonary cryptococcosis.

• Cytomegalovirus disease of an organ other than liver, spleen or lymph nodes.

• Herpes simplex virus infection, mucocutaneous >one month, or visceral any duration.

• Progressive multifocal leukoencephalopathy.

• Any disseminated endemic mycosis (i.e. histoplasmosis, coccidioidomycosis).

• Candidiasis of the oesophagus, trachea, bronchi or lungs .

• Disseminated atypical mycobacteriosis.

• Non-typhoid Salmonella septicaemia.

• Extrapulmonary tuberculosis.

• Lymphoma.

• Kaposis sarcoma.

• HIV encephalopathy, as defined by the Centers for Disease Control and Prevention.

• Performance scale 4: bedridden for more than 50% of the day during the last month.

Note: both definitive and presumptive diagnoses are acceptable.

HIV wasting syndrome: weight loss of >10% of body weight, plus either unexplained chronic diarrhoea

(>1 month) or chronic weakness and unexplained prolonged fever (>1 month).

HIV encephalopathy: clinical findings of disabling cognitive and/or motor dysfunction interfering with activities of daily living, progressing over weeks to months, in the absence of a concurrent illness or condition other than HIV infection which could explain the findings.

Children

Two major and two minor signs are required in the absence of known causes of immunosuppression.

Major signs are defined as:

• Weight loss or abnormally slow growth.

• Diarrhoea lasting more than one month.

• Fever lasting more than one month.

Minor signs are defined as:

• Persistent generalised lymphadenopathy.

• Candida in the mouth or oesophagus.

• Cough lasting more than one month.

• Widespread itchy rash.

• Repeated common infection (otitis, sore throat etc).

• Confirmed maternal HIV infection.

The WHO criteria for both children and adults have been criticised by Gilks and Muller as being too insensitive (i.e. they do not pick up all the paediatric cases of AIDS) and too non-specific (they mistakenly diagnose some children as having AIDS).