Epidemiology of human immunodeficiency virus infection and associated neurologic illness

Worldwide, 30 million people are infected with the human immunodeficiency virus (HIV), with almost 6 million new infections in 1997. Recent therapeutic advances, which have altered the natural history of HIV infection, and changes in the AIDS case definition, both complicate evaluations of temporal changes in AIDS incidence and prevalence, and lesson the utility of AIDS incidence as a proxy for monitoring the HIV epidemic. The highest AIDS incidence rates in the United States are in black men. Rates are increasing most quickly in women, minorities, and adolescents and young adults, largely due to heterosexual transmission and intravenous drug abuse. Survival after diagnosis of AIDS is associated most strongly with the initial AIDS-defining diagnosis, and patients with neurologic opportunistic infections or primary central nervous system (CNS) lymphoma have shorter survival periods. Neurological illnesses are the initial manifestation of AIDS in 7% to 20% of patients, but the frequency of neurologic complications increases over the course of the illness. The most common AIDS-defining opportunistic illnesses are HIV encephalopathy, CNS toxoplasmosis, cytomegalovirus retinitis, and primary CNS lymphoma. Primary prevention of HIV infection is accomplished by changing factors that enable transmission, through behavioral changes, utilization of antiretroviral agents to prevent vertical transmission, and through securing the safety of the blood supply. Secondary prevention, involving early detection and prompt treatment, has become important in developed countries since the introduction of powerful antiretroviral therapies and has contributed to the 46% decline in AIDS deaths in the United States from 1996 to 1997. Inequality of access to effective therapies and emergence of multi-drug-resistant strains of HIV have raised serious concerns.