Each year, an estimated 56,300 people in the U.S. become newly infected with HIV, the virus that causes AIDS.

This number is so high in part because about one-quarter of the more than 1.1 million Americans believed to be living with HIV don’t know they are infected, according to the Centers for Disease Control and Prevention.

HIV is transmitted primarily through sexual intercourse or contact with infected blood, semen, or cervical and vaginal fluids; injection-drug use; and perinatally from infected mothers to their infants. HIV transmission has also been reported in recipients of blood, blood-containing organs such as the kidney, liver, heart pancreas, bone, and skin or highly vascular tissues from HIV-infected donors.

However, improvements in donor education, donor screening and blood testing has resulted in a continued decrease in the risk of transfusion and organ transplant transmission of HIV—improvements that now include a new test that detects the presence of antibodies for both types of HIV.

New Test

Approved by the U.S. Food and Drug Administration (FDA) on Friday, the Abbott Prism HIV O Plus assay is licensed for screening donated blood and blood specimens from other living donors, and for screening specimens from organ donors when specimens are obtained while the donor’s heart is still beating and from cadavers. Positive results from the test require confirmation from supplemental tests. The assay is one of five tests that run on Illinois-based Abbott’s Prism System, a fully automated instrument also used to test blood for hepatitis.

Both types of HIV have been detected in the United States and Europe. Type 1, which consists of various subgroups, including group M, the most common subgroup of the virus in the United States, and group O, found primarily in Cameroon and other areas of West Africa; and type 2, which is found primarily in West Africa. Once HIV enters the body, the body starts to produce cells and particles to fight the virus called antibodies. The HIV antibodies are different from antibodies for the flu, a cold, or other infections. 

Before 1985, there were no tests to screen blood and organ donations for HIV. Today, blood and organ banks screen out most potential donors at risk for infection in advance through extensive testing. The risk of acquiring HIV from a blood transfusion today is estimated to be 1 in 4 for every 600,000 transfusions. The risk of acquiring HIV from organ transplantation is probably similar.

Most HIV tests look for these antibodies rather than the virus itself. Previously, the two primary blood tests used to detect the HIV antibodies were the enzyme-linked immunosorbent assay (ELISA), and the Western blot assay, used to confirm the results of a positive ELISA test. These tests do not tell how long a person has been infected, how sick they might be, or if they have AIDS (acquired immune deficiency syndrome), which is the final and most serious stage of HIV disease.

State of the Epidemic

AIDS is the fifth leading cause of death among people aged 25-44 in the United States, down from number one in 1995. About 25 million people worldwide have died from this infection since the start of the epidemic, and in 2006, there were approximately 40 million people worldwide living with HIV/AIDS.