WHO Disease Staging System for HIV Infection and Disease in Adults and Adolescents was first produced in 1990 by the World Health Organization and updated in September 2005. It is an approach for use in resource limited settings and is widely used in Africa and Asia and has been a useful research tool in studies of progression to symptomatic HIV disease. Following infection with HIV, the rate of clinical disease progression varies enormously between individuals. Many factors such as host susceptibility and immune function, health care and co-infections, as well as factors relating to the viral strain may affect the rate of clinical disease progression. Revised World Health Organization (WHO) Clinical Staging of HIV/AIDS For Adults and Adolescents (2005) (This is the interim African Region version for persons aged 15 years or more who have had a positive HIV antibody test or other laboratory evidence of HIV infection) (The United Nations defines adolescents as persons aged 10−19 years but for surveillance purposes, the category of adults and adolescents comprises people aged 15 years and over) Primary HIV infection Asymptomatic Acute retroviral syndrome Clinical stage 1 Asymptomatic Persistent generalized lymphadenopathy Clinical stage 2 Moderate and unexplained weight loss (<10% of presumed or measured body weight) Recurrent respiratory tract infections (such as sinusitis, bronchitis, otitis media, pharyngitis) Herpes zoster Recurrent oral ulcerations Papular pruritic eruptions Angular cheilitis Seborrhoeic dermatitis Onychomycosis (fungal nail infections) Clinical stage 3 Conditions where a presumptive diagnosis can be made on the basis of clinical signs or simple investigations Unexplained chronic diarrhoea for longer than one month Unexplained persistent fever (intermittent or constant for longer than one month) Severe weight loss (>10% of presumed or measured body weight) Oral candidiasis Oral hairy leukoplakia Pulmonary tuberculosis (TB) diagnosed in last two years Severe presumed bacterial infections (e.g. pneumonia, empyema, meningitis, bacteraemia, pyomyositis, bone or joint infection) Acute necrotizing ulcerative stomatitis, gingivitis or periodontitis Conditions where confirmatory diagnostic testing is necessary Unexplained anaemia (< 80 g/L), and or neutropenia (<500/μl) and or thrombocytopenia (<50 000/ μl) for more than one month Clinical stage 4 Conditions where a presumptive diagnosis can be made on the basis of clinical signs or simple investigations HIV wasting syndrome Pneumocystis pneumonia Recurrent severe or radiological bacterial pneumonia Chronic herpes simplex infection (orolabial, genital or anorectal of more than one month's duration) Esophageal candidiasis Extrapulmonary tuberculosis Kaposi's sarcoma Central nervous system toxoplasmosis HIV encephalopathy Conditions where