Global Alert and Response (GAR)

WHO Report on Global Surveillance of Epidemic-prone Infectious Diseases - Human Immunodeficiency Virus and Acquired Immune Deficiency Syndrome (HIV/AIDS)


HIV is easily killed outside the human body and therefore can only be transmitted directly from person to person, either by sexual contact, exchange of blood or body fluids or from mother to child. Sexual transmission of HIV is relatively inefficient and repeated unprotected exposures are normally required. Since the global HIV epidemic is driven mainly by sexual transmission, the level and intensity of risk behaviours (vaginal or anal unprotected sex) in a given community are the main determinants of the spread of the virus. Therefore, HIV incidence and prevalence can vary greatly from country to country and even within countries, depending on several factors, some well documented and others still being investigated. These factors may determine the probability of exposure to HIV infection (e.g. level and extent of risk behaviours, high HIV prevalence in the community), others may influence the probability of HIV transmission per exposure (e.g. the prevalence of other sexually transmitted infections (STIs), levels of condom use, circumcision). In view of the importance of these determinants, information from behavioural surveillance studies and STI incidence and prevalence can help better explain epidemic curves and monitor the impact of interventions. The concept of 2nd generation HIV surveillance, introduced by WHO and UNAIDS, integrates AIDS and HIV surveillance with additional sources of essential data to better monitor the epidemic (1).

Map 9.1 Estimated percentage of adults (15-49 years old) infected with HIV, as of 1999 (2)

Map 9.1 Estimated percentage of adults (15-49 years old) infected with HIV, as of 1999 (2)


(1) Guidelines for second generation HIV surveillance. World Health Organization and UNAIDS, 2000, WHO/CDS/EDC/2000.5.

(2)Source: Report on the global HIV/AIDS epidemic, UNAIDS/CO.13E.