What Is HIV?

The human immunodeficiency virus, or HIV, is a virus that attacks the body’s immune system. Specifically, the virus infects people’s CD4-positive (CD4+) T-helper cells. Those cells — sometimes known as CD4 cells, T-helper cells, or T4 cells — are white blood cells that play an important role in the immune system. Over time, HIV can destroy CD4 cells, impairing the immune system’s ability to fight off infections and diseases. The final stage of an HIV infection is called acquired immunodeficiency syndrome, or AIDS. AIDS is a life-threatening disease, and occurs when your immune system is severely damaged. AIDS is diagnosed when your CD4 cells are very low — fewer than 200 cells per cubic millimeter of blood, compared with the “normal” count of 500 to 1,600 cells per cubic millimeter — or when you develop one or more opportunistic illnesses, such as pneumonia or tuberculosis, as a result of an HIV infection and a compromised immune system. Opportunistic infections are infections that occur more frequently or are more severe in people with weakened immune systems.

Prevalence and Demographics

There were an estimated 39,782 new cases of HIV diagnosed in the United States in 2016, according to the latest figures available from the Centers for Disease Control and Prevention (CDC). The CDC further estimates that some 1.1 million Americans were living with HIV in 2015, and about 15 percent (or 1 in 7) of those people didn’t know they were infected. Anyone can contract HIV, but the devastating virus doesn’t affect different groups of people equally. Of the estimated 38,500 new U.S. HIV infections in 2015, about two-thirds of the newly infected people were bisexual or gay men, according to CDC data. Different races and ethnicities also experience skewed HIV infection rates. In 2015, African-Americans, whites, and Hispanic or Latinos accounted for 42 percent, 26 percent, and 26 percent of new HIV cases in the United States, respectively. Despite greatly improved treatment options available since the AIDS outbreak in the 1980s, people still die from the disease. In 2015, AIDS caused the death of 6,565 people in the United States, bringing the total AIDS death toll in the country to 507,351 people, according to the CDC. Globally, HIV and AIDS remain a serious problem, with an estimated 1.8 million new cases of HIV and 36.9 million people living with the virus in 2017, according to the World Health Organization (WHO).  Today, people in sub-Saharan Africa bear the brunt of the current HIV epidemic, with 25.7 million people living with HIV in 2017 and accounting for nearly two-thirds of new HIV infections worldwide, according to the WHO. According to the WHO, HIV has infected more than 70 million people worldwide since the epidemic began decades ago, and about 35 million people have died.