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AIDS was originally defined empirically by the Centers for Disease Control and Prevention (CDC) as "the presence of a reliably diagnosed disease that is at least moderately indicative of an underlying defect in cell-mediated immunity." Following the recognition of the causative virus, HIV, and the development of sensitive and specific tests for HIV infection, the definition of AIDS has undergone substantial revision. The current surveillance definition categorizes HIV-infected persons on the basis of clinical conditions associated with HIV infection and CD4+ T lymphocyte counts (Tables 189-1, and 189-2, pp. 1506 and 1507, in HPIM-18). From a practical standpoint, the clinician should view HIV disease as a spectrum of disorders ranging from primary infection, with or without the acute HIV syndrome, to the asymptomatic infected state, to advanced disease.


AIDS is caused by infection with the human retroviruses HIV-1 or -2. HIV-1 is the most common cause worldwide. These viruses are passed through sexual contact; through transfusion of contaminated blood or blood products; through sharing of contaminated needles and syringes among injection drug users; intrapartum or perinatally from mother to infant; or via breast milk. There is no evidence that the virus can be passed through casual or family contact or by insects such as mosquitoes. There is a definite, though small, occupational risk of infection for health care workers and laboratory personnel who work with HIV-infected specimens. The risk of transmission of HIV from an infected health care worker to his or her pts through invasive procedures is extremely low.


As of January 1, 2010, an estimated 1,108,611 cumulative cases of AIDS had been diagnosed in the United States; there have been approximately 600,000 deaths due to AIDS. However, the death rate from AIDS has decreased substantially in the past 10 years primarily due to the increased use of potent antiretroviral drugs. As of January 1, 2010, an estimated 1.1 million HIV-infected persons were living in the United States; approximately 21% of these individuals are unaware that they are infected. An estimated 56,000 individuals are newly infected each year in the United States; this figure has remained stable for at least 15 years (Fig. 189-12, p. 1518, in HPIM-18). Among adults and adolescents newly diagnosed with HIV infection in 2009, ∼76% were men and ∼24% were women. Of new HIV/AIDS diagnoses among men, ∼75% were due to male-to-male sexual contact, ∼14% to heterosexual contact, and ∼8% to injection drug use. Among women, ∼85% were due to heterosexual contact and ∼15% to injection drug use (Figs. 189-13 and 189-14, p. 1519, in HPIM-18). HIV infection/AIDS is a global pandemic, especially in developing countries. At the end of 2009, the estimated number of cases of HIV infection worldwide was ∼33.3 million, two-thirds of which were in sub-Saharan Africa; ∼50% of cases were in women and 2.5 million were ...

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