HIV (human immunodeficiency virus) is the virus that causes AIDS (acquired immunodeficiency syndrome). HIV progressively destroys the body's ability to fight infections and certain cancers. It weakens the immune system by infecting lymphocytes, a type of white blood cell, that normally help the body fight infections. Specific lymphocytes known as T-helper cells or CD4 cells are major targets for HIV. The virus binds to CD4 cells, enters them, replicates inside them, and eventually kills them.
Over time, the amount of HIV virus—the viral load—increases while the number of CD4 cells in the blood declines. After several years without treatment, the number of CD4 cells can drop to the point that AIDS-associated conditions and symptoms begin to appear. AIDS treatments can slow disease progression by reducing the amount of HIV in the body. This allows the body's CD4 cells to increase or stabilize.
Currently, the Centers for Disease Control and Prevention (CDC) estimates that about 50,000 people in the U.S are newly infected with HIV each year, that 1.2 million people in the U.S. are living with HIV infection, and that nearly 13% of those with the infection are not aware of it and can pass the virus on to others. In 2012, the year with the most current statistics, nearly 14,000 people with AIDS died, and almost 660,000 have died since the beginning of the epidemic, according to the CDC.
Worldwide, as many as 2.1 million people in 2013 were newly infected with HIV, 1.5 million died of AIDS-related illnesses, and 35 million people were living with HIV, according to the World Health Organization.
HIV can be spread the following ways:
- By having unprotected sex with an infected partner; the virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex. Having a sexually transmitted disease (STD) such as syphilis, genital herpes, chlamydia, gonorrhea, or bacterial vaginosis appears to make people more susceptible to and at higher risk for acquiring HIV infection during sex with infected partners.
- By sharing needles or syringes (such as with intravenous injection drug abuse), which can be contaminated with very small quantities of blood from someone infected with the virus.
- During pregnancy or birth; approximately 25% to 35% of all untreated pregnant women infected with HIV will pass the infection to their babies. HIV also can be spread to babies through the breast milk of mothers infected with the virus. If the mother is treated with antiretroviral therapy (ART) during pregnancy, she can significantly reduce the chances of passing the infection to her baby.
- Through contact with infected blood; in the U.S. today, because of screening blood for transfusion and heat-treating techniques and other treatments of blood derivatives, the risk of getting HIV from transfusions is extremely small. However, before donated blood was screened for evidence of HIV infection and before treatments were introduced to destroy HIV in some blood products, such as factor VIII and albumin, HIV was transmitted through transfusion of contaminated blood or blood components. In areas of the world where donated blood is not routinely screened or treated for HIV, there is still risk of contracting the disease through this mode of transmission.
Initially, HIV usually causes flu-like symptoms, but some people may not experience any obvious signs or symptoms. The only way to determine whether a person has been infected is through HIV testing.
A person's HIV status, like other medical conditions and test results, is protected by the Health Insurance Portability and Accountability Act (HIPAA) Privacy Rule and cannot be shared by healthcare providers with friends, family, or employers without written permission. However, if a person tests positive for HIV, it is important that he or she tell their healthcare providers as well as all sex partners and/or anyone with whom they share needles. Counseling services are often available from the clinic or healthcare provider that performed the test and they can help to advise the individual on who needs to know.
HIV status may be shared with healthcare providers who have a "need to know" in order to treat an individual. Also, in order to determine the incidence of HIV and to provide appropriate prevention and care services, all new cases of HIV are reported to state and local health departments. As of April 2008, data from all 50 states, the District of Columbia, and 5 dependent areas (American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands) are collected using a confidential name-based reporting system.
Development of AIDS
HIV initially causes an acute illness with non-specific, flu-like symptoms. During this time, the virus is present in large numbers and is carried throughout the body. About 2 to 8 weeks after exposure, the person's immune system responds by producing antibodies against the virus. As HIV infects the immune cells called CD4 T-cells (also called helper T cells), it slowly begins to decrease their numbers. The person may be apparently healthy for a decade or more, but without treatment, HIV continues to replicate and destroy CD4 T-cells. The virus remains in places such as the brain and lymph nodes, where it will persist even during drug treatment.
The term AIDS applies to the most advanced stages of HIV infection. According to the CDC, AIDS is diagnosed when an individual's CD4 T-cell count drops below 200 cells/mm3. AIDS is also diagnosed when an individual has HIV and an AIDS-related illness, such as tuberculosis or pneumonia caused by the microorganism Pneumocystis jirovecii (carinii). In people with AIDS, opportunistic infections are often severe and sometimes fatal because the immune system is so damaged by HIV that the body cannot fight off certain bacteria, viruses, fungi, or parasites. Those with HIV/AIDS are also at an increased risk of developing certain cancers, neurological disorders, and a variety of other conditions.