HIV infections have declined by 73 percent nationwide since peaking in the mid-1980s, according to the Centers for Disease Control and Prevention. New infections numbered 20,000 in 1981, reaching 130,400 in 1984 before declining to 34,800 by 2019, the CDC reported recently. HIV — the human immunodeficiency virus — attacks cells that the body needs to fight infection. If untreated, an HIV infection can lead to AIDS (acquired immunodeficiency syndrome). In the 40 years since the onset of the AIDS epidemic, 2.2 million people 13 and older in the United States have developed an HIV infection. Today, about 1.2 million people in the country are living with HIV, including more than half (57 percent) whose treatment has prevented the disease from progressing, the CDC says. The federal agency says, however, that about 13 percent do not know they have HIV and should be tested. While there is no effective cure for HIV, there are treatments — a daily pill regimen and a recently approved every-four-weeks injectable — that can keep it in check, as a chronic and manageable condition, and prevent it from progressing to AIDS. HIV is spread by contact with bodily fluids from a person with HIV, most often during unprotected sex or the sharing of injection drug paraphernalia, such as needles. The CDC report attributes most infections (63 percent in 1981, 66 percent in 2019) to male-to-male sexual contact. By contrast, HIV infections among those who inject drugs have dropped by 93 percent (from 34,500 in 1988-1990 to 2,500 in 2019).