<P> Antibody tests in children younger than 18 months are typically inaccurate due to the continued presence of maternal antibodies . Thus HIV infection can only be diagnosed by PCR testing for HIV RNA or DNA, or via testing for the p24 antigen . Much of the world lacks access to reliable PCR testing and many places simply wait until either symptoms develop or the child is old enough for accurate antibody testing . In sub-Saharan Africa as of 2007--2009, between 30 and 70% of the population were aware of their HIV status . In 2009, between 3.6 and 42% of men and women in Sub-Saharan countries were tested which represented a significant increase compared to previous years . </P> <P> Two main clinical staging systems are used to classify HIV and HIV - related disease for surveillance purposes: the WHO disease staging system for HIV infection and disease, and the CDC classification system for HIV infection . The CDC's classification system is more frequently adopted in developed countries . Since the WHO's staging system does not require laboratory tests, it is suited to the resource - restricted conditions encountered in developing countries, where it can also be used to help guide clinical management . Despite their differences, the two systems allow comparison for statistical purposes . </P> <P> The World Health Organization first proposed a definition for AIDS in 1986 . Since then, the WHO classification has been updated and expanded several times, with the most recent version being published in 2007 . The WHO system uses the following categories: </P> <Ul> <Li> Primary HIV infection: May be either asymptomatic or associated with acute retroviral syndrome . </Li> <Li> Stage I: HIV infection is asymptomatic with a CD4 T cell count (also known as CD4 count) greater than 500 per microlitre (μl or cubic mm) of blood . May include generalized lymph node enlargement . </Li> <Li> Stage II: Mild symptoms which may include minor mucocutaneous manifestations and recurrent upper respiratory tract infections . A CD4 count of less than 500 / μl . </Li> <Li> Stage III: Advanced symptoms which may include unexplained chronic diarrhea for longer than a month, severe bacterial infections including tuberculosis of the lung, and a CD4 count of less than 350 / μl . </Li> <Li> Stage IV or AIDS: severe symptoms which include toxoplasmosis of the brain, candidiasis of the esophagus, trachea, bronchi or lungs and Kaposi's sarcoma . A CD4 count of less than 200 / μl . </Li> </Ul>

When was the term 'aids' first defined