Within 3 years after the syndrome was recognized in the United States, cases of AIDS were reported from every continent. By November of 1997, more than 1.7 million cases had been reported from 197 countries to WHO (Table 409-4) . WHO also estimates that >60 milion people would be infected with HIV by the end of century.
AIDS case reporting from developing countries is much less complete than in industrialized countries and, because the developing world is most heavily affected by HIV/AIDS, WHO estimates that the number of reported AIDS cases worldwide are less than 15% of the total estimated number of AIDS cases that have occurred throughout the epidemic. Extensive HIV serosurveys in Africa, South and Central America, and parts of Asia provide evidence that AIDS case reports greatly underestimate the magnitude of the HIV problem in many countries in these regions.
Modes of transmission of HIV are similar throughout the world, but the relative frequency varies considerably between countries and regions. In North America, Europe, Australia, New Zealand, and some areas of South America, the majority of HIV infections first occurred in homosexual men and IDUs; heterosexual and perinatal transmission initially resulted mostly from transmission from IDUs and their partners. In most countries in Africa and some in the Caribbean and Central America, most HIV infections have occurred through heterosexual transmission.
HIV seroprevalence rates are highest in urban prostitutes and sexually active young adults. High rates of infection in young women translate into a substantial amount of perinatal transmission. In some areas of Africa, pediatric HIV infection has significantly increased already high infant mortality rates. In many developing countries, transfusion of HIV-infected blood remains a substantial problem because of inadequate blood banking and serologic testing capacity. Reuse of nonsterile needles and syringes and other medical practices have caused major HIV outbreaks in the former Soviet Union and Romania. In Asian countries such as Thailand and India, emergence of HIV infection as a major public health problem began in IDUs and prostitutes, but rapidly spread more widely through heterosexual transmission to other young adult populations. India is now the country believed to have the highest number of HIV-infected persons, with an estimated 2 to 5 million people currently infected.
In Eastern Europe and the newly independent states of the former Soviet Union, HIV infections are rapidly increasing, primarily in association with injecting drug use. In yet other countries, primarily in the Middle East, Asia, and the Pacific region, HIV has not yet been recognized as an important public health problem. The future course of HIV in these countries may depend on their ability to anticipate and respond to the problem; it can be approximately predicted by the extent and pattern of sexually transmitted and transfusion-associated infections and the extent of injecting drug use that currently exists in each country.
A second human immunodeficiency virus, HIV type 2 (HIV-2), was first described in asymptomatic West Africans with AIDS in 1986. HIV-2 infection remains most prevalent in West Africa, although well-documented cases have been reported from Western Europe, Canada, Brazil, the United States, and Central Africa. HIV-2 is generally less virulent than HIV-1. The average viral titer usually is lower, perhaps explaining the lower rates of sexual and perinatal transmission and the slower rate of disease progression in persons infected with HIV-2 than HIV-1. HIV-1 and HIV-2 are closely related; tests for antibody for one virus often cross react with those for the other.
For example, licensed enzyme immunoassays for detecting HIV-1 find HIV-2 antibody in 60 to 90% of infected patients. In the United States, combined HIV-1/HIV-2 assays are used to test donated blood. As of 1994, HIV-2 infection remained rare in the United States, with nearly all cases detected in persons from West Africa.
Recently, additional HIV variants, classified together as subtype O, were reported from Cameroon. The antibody response elicited by group O strains is not consistently detected by enzyme immunoassay (EIA) kits commercially available in Europe and the United States. In 1996, a patient with HIV-1 group O infection was diagnosed in California, which reinforces the need for strong international collaboration in maintaining surveillance for variants of HIV and other emerging infections.
- HIV infection and AIDS in the United States
- Indicence and trends of AIDS in the United States
- Modes of HIV Transmission
- Other Modes of Transmission
- Perinatal Transmission
- Prevalence and Incidence of HIV Infection in the United States
- Transmission in the Health Care Environment
- Transmission Through Parenteral Exposure to Blood or Blood Products
Goedert JJ, Eyster EE, Biggar RJ, et al: Heterosexual transmission of HIV: Association with severe depletion of T-helper lymphocytes in men with hemophilia. AIDS Res Hum Retroviruses 3:355, 1988. Holmberg SD, Horsburgh CR, Ward JW, et al: Biologic factors in the sexual transmission of human immunodeficiency virus. J Infect Dis 160:116, 1989. Ellerbrock TV, Lieb S, Harrington PE, et al: Heterosexual transmitted human immunodeficiency virus infection among pregnant women in a rural Florida community. N Engl J Med 327:1704, 1992. De Vincenzi I, et al: A longitudinal study of human immunodeficiency virus transmission by heterosexual partners. N Engl J Med 331:341, 1994. Connor EM, Sperling RS, Gelber R, et al: Reduction of maternal-infant transmission of human immunodeficiency virus type 1 with zidovudine treatment. N Engl J Med 331:1173, 1994. CDC: Perinatally acquired HIV/AIDS-United States, 1997. MMWR 46:1086, 1997. CDC/USPHS Task
Force Recommendations for the Use of Antiretroviral Drugs in Pregnant Women Infected with Human Immunodeficiency Virus-1 for Maternal Health and for Reducing Perinatal HIV-1 Transmission in the U.S. MMWR 47 (RR-2):1, 1998. These summarize available information on factors related to heterosexual transmission of HIV and prevention of perinatal transmission.
Mann JM, Tarantola DJM (eds): AIDS in the World II Global Dimensions, Social Roots and Responses. New York: Oxford University Press, 1996. This volume summarizes and updates what is known about HIV infection and prevention activities throughout the world.
1993 Revised classification system for HIV infection and expanded surveillance, case definition for AIDS among adolescents and adults. MMWR 41(RR-17):1, 1992. Redfield RR, Wright DC, Tramont EA: The Walter Reed staging classification for HTLV-IIILAV infection. N Engl J Med 314:131, 1986. These are the most widely used classification systems in the United States.
Update: Trends in AIDS incidence, deaths, and prevalence-United States, 1996. JAMA 277:874, 1997. CDC: AIDS among racial/ethnic minorities-United States, 1993. MMWR 43:644, 1993. Denning PH, et al: Recent trends in the HIV epidemic in adolescent and young adult gay and bisexual men. JAIDS 16:374, 1997. Karon JM, et al: Prevalence of HIV infection in the United States, 1984 to 1992. JAMA 276:126, 1996. McQuillan GM, et al: Update on the seroepidemiology of human immunodeficiency virus in the United States household population: NHANES III, 1988-1994. JAIDS 14:355, 1997. Weainstock HS, et al: Trends in HIV seroprevalence among persons attending sexually transmitted disease clinics in the United States, 1988-1992. JAIDS 9:514, 1995. Pub Health Rep 105:113, 1990. National serosurveillance summary, Volume 3-Centers for Disease Control and Prevention, HIVNCID11-913036; Gwinn M, Pappaioanou M, George JR, et al: Prevalence of HIV infection in childbearing women in the United States. JAMA 265:1704, 1991. These articles summarize recent methods and data on HIV seroprevalence in the United States.
Update: Universal precautions for prevention of transmission of HIV, hepatitis B virus, and other bloodborne pathogens in health care setting. MMWR 37:337, 1988. Public Health Service Guidelines for the Management of Health-Care Worker Exposures to HIV and Recommendations for Postexposure Prophylaxis. MMWR 47 (RR-7):1, 1998. Recommendations for preventing transmission of human immunodeficiency virus and hepatitis B virus to patients during exposure-prone invasive procedures. MMWR 40(RR-8):1, 1991. These documents summarize data on transmission of HIV in the health care setting and list recommended precautions.
Revision date: July 7, 2011
Last revised: by Jorge P. Ribeiro, MD