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Human immunodeficiency virus (HIV) is the cause of HIV infection. HIV infects a specific type of immune system cells called CD4 lymphocytes or T-helper cells. The role of healthy CD4 cells is to organize other immune cells to respond to infection, effectively stimulating the immune response. When HIV infects a CD4 cell, it hijacks the process by which the cell replicates itself and uses it to produce copies of HIV instead, releasing them into the body to infect more CD4 cells. HIV also destroys CD4 cells, making it difficult for the body to coordinate an immune response to invading pathogens such as viruses or bacteria. Lowered levels of CD4 cells weaken the immune system and leave the body unable to protect itself from cancer and infections.
DNA and RNA are different types of molecules used to communicate genetic instructions. Most viruses translate DNA into RNA, which instructs the cell on which proteins to produce. HIV is known as a retrovirus due to its ability to reverse the usual process, translating its RNA into DNA and inserting it into the nucleus of the cell, which then reproduces more HIV.
In people infected with HIV, the virus is carried in blood, semen, pre-seminal fluid, vaginal secretions, rectal fluid, and breast milk. In order to spread HIV, the infected fluid must come into contact with the uninfected person in one of three specific ways:
HIV is most commonly passed during anal or vaginal sex without condoms or by sharing used needles or other injection equipment. HIV can also be spread by contaminated blood transfusions or tissue transplants, improperly sanitized medical, dental, or tattoo instruments, and from mother to baby during pregnancy, birth, or breastfeeding. It is extremely rare but possible to contract HIV from oral sex or deep kissing if there are open wounds – for instance, bleeding gums.
Using a new synthetic (latex or polyurethane) condom every time you have vaginal or anal sex is extremely effective for preventing HIV transmission. To be effective, the condom must be put on correctly before penetration begins. Note that “natural” condoms, such as those made from the intestinal membranes of lambs, do not prevent the transmission of HIV.
When a person who is HIV-negative consistently takes the treatment regimen known as pre-exposure prophylaxis (PrEP), their risk for contracting HIV via sex with an infected partner is reduced by more than 90 percent. PrEP reduces the risk for contracting HIV from sharing needles with an infected person by more than 70 percent.
After being on treatment for several months, many HIV-positive people can bring their viral load (the measure of HIV virus in their blood) down to such low levels that it is undetectable. People with an undetectable viral load (UVL) are believed to be incapable of spreading HIV to others as long as they continue to consistently take treatment.
Decades ago, when little was known about HIV and AIDS, people were not sure exactly how the virus was transmitted. Myths surrounding HIV persist, and some people still fear close contact with those who have HIV. However, clinical studies have proven that HIV cannot survive outside the body – including on skin, in water, or in the air – and many bodily fluids do not carry HIV. The following bodily fluids and types of contact cannot transmit HIV between people:
Anyone – regardless of age, sex, sexual orientation, or ethnic background – can become infected with HIV.
Lifestyle choices and other behavioral factors have the most influence over who gets HIV.
High-risk behaviors include:
During sex, the person receiving penetration (the “bottom”) has the highest risk for contracting HIV. The person performing penetration (the “top”) has the highest risk for transmitting HIV.
Risk for contracting HIV increases if you have other sexually transmitted infections (STIs) such as herpes. In fact, having an STI doubles the risk for HIV infection in HIV-negative individuals who have sex with an HIV-positive person of the opposite sex.
Uncircumcised men are more likely to contract HIV than those who are circumcised. Studies have shown that circumcised men are 60 percent less likely to contract HIV during sex with a woman than those who are uncircumcised.
Sexual orientation, sex, ethnicity, and geographic area all influence the risk for contracting HIV.
Gay and bisexual men have the highest rate of HIV infection, making up 67 percent of those diagnosed in the U.S.
Ethnic background has a strong influence over HIV risk. In the U.S., people of African descent accounted for 44 percent of HIV diagnoses in 2016 although they make up only 12 percent of the population. People of Latino or Hispanic background also have a higher risk for contracting HIV.
In general, women are less likely to contract HIV than men. In 2016, women made up about 19 percent of new HIV diagnoses in the U.S. However, transgender women who have sex with men have a high rate of HIV infection.
People in their 20s and 30s are more likely to be diagnosed with HIV than those in other age groups.
Risk for HIV infection varies by geographic region in the U.S. In 2016, more than half of new HIV infections were in the southern states. Only 38 percent of the U.S. population live in the South.