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 in the absence of any known cause for such a defect.” 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 197-1, and 197-2, in HPIM-20). 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 characterized by opportunistic infections and neoplasms.
ETIOLOGY AND TRANSMISSION
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 (IDUs); intrapartum or perinatally from mother to infant; or via breast milk. There is a definite, though small, occupational risk of infection for health care workers and laboratory personnel who work with HIV-infected specimens, usually through injury from contaminated sharp instruments. 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 November 1, 2017, an estimated 1.8 million people have been infected with HIV and 1.1 million people are currently living with HIV in the United States; approximately 13% of these individuals are unaware that they are infected. Approximately 693,000 people with an AIDS diagnosis have died. However, the death rate from AIDS has decreased substantially over the past two decades, primarily due to the increased use of effective antiretroviral drugs. An estimated 40,000 individuals are newly infected each year in the United States; this figure has remained stable for at least 15 years. Among adults and adolescents newly diagnosed with HIV infection in 2017, ∼80% were men and ∼20% were women. Of new HIV/AIDS diagnoses, 68% were due to male-to-male sexual contact, 23% to heterosexual contact, and 6% to IDUs. HIV infection/AIDS is a global pandemic, especially in developing countries. At the end of 2017, the estimated number of cases of HIV infection worldwide was ∼36.9 million, more than two-thirds of which were in sub-Saharan Africa; ∼47% of cases were in women and 2.6 million were in children. In 2017, there were 1.8 million new HIV infections worldwide and 940,000 deaths.
PATHOPHYSIOLOGY AND IMMUNOPATHOGENESIS
The hallmark of HIV disease is a profound immunodeficiency resulting from a progressive quantitative ...