Understanding how HIV can and cannot be transmitted is at the core of preventing new infections. HIV is a rapidly changing virus but, thankfully, it is also entirely preventable. In this section, you can learn more about how HIV is transmitted and how to reduce your, or others’, risk of being infected. Below are several key points to understand with HIV transmission.
HIV Must Be Present
Infection may only occur if one of the people involved in an exposure situation is infected with HIV. Some people assume that certain behaviors or exposure situations can cause HIV disease, even if the virus is not present. This is not true.
There Needs to Be Enough Virus
The concentration of HIV determines whether infection will occur. In blood, for example, the virus is very concentrated. A small amount of blood is enough to infect someone. The concentration of virus in blood or other fluids can change, in the same person, over time. Persons who take HIV medications as prescribed can have very low quantities of HIV present in bodily fluids, greatly reducing the risk of transmitting HIV to their partners.
It is important to note that HIV is a very fragile virus which will die quickly when exposed to light and air. Exposure to small amounts of dried blood or other infectious fluids is not a realistic risk for HIV transmission.
HIV Must Get Into the Bloodstream
It is not enough to be in contact with an infected fluid for HIV to be transmitted. Healthy, intact skin does not allow HIV to get into the body.
HIV can enter through an open cut or sore, or through contact with mucous membranes. Transmission risk is very high when HIV comes in contact with the more porous mucous membranes in the genitals, the anus, and the rectum which are inefficient barriers to HIV. Although very rare, transmission is also possible through oral sex because body fluids can enter the bloodstream through cuts in the mouth.
Infectious Fluids – HIV can be transmitted from an infected person to another through:
- Semen (including pre–seminal fluid)
- Vaginal secretions
- HIV can also be transmitted through breast milk expressed through feeding, in limited circumstances, where there is exposure to large quantities.
HIV Transmission Routes
HIV can enter the body through open cuts or sores and by directly infecting cells in mucous membranes. HIV cannot cross healthy, unbroken skin. Unprotected sexual intercourse (oral, vaginal, and anal), sharing needles for injection drug use and mother to child transmission (in utero, during delivery, and breastfeeding) are the main transmission routes for the HIV virus.
Sexual activity is the most common way for HIV to be transmitted. HIV can be transmitted through sexual intercourse, both vaginal and anal. HIV can easily pass through the mucus membranes in the genitals and the rectum, or may pass through cuts and sores.
Although very rare, HIV can also be transmitted through oral sex. Conditions such as bleeding gums and poor oral health increase the risk of transmission through oral sex.
Anal sex without a condom is the riskiest activity for HIV transmission. The receptive partner is at the greatest risk because anal tissue is easily bruised or torn during sex which then provides easy access to the bloodstream for HIV carried in semen. The insertive partner is also at some risk because the membranes inside the urethra can provide entry for HIV into the bloodstream. The presence of other sexually transmitted infections can increase the risk of HIV transmission during anal sex.
Unprotected vaginal sex is also considered risky for HIV transmission. The female is at the greatest risk because the lining of the vagina is a mucous membrane which can provide easy access to the bloodstream for HIV carried in semen. The male is also at some risk because the membranes inside the urethra can provide an entry for HIV into the bloodstream. The presence of other sexually transmitted infections can increase the risk of HIV transmission during vaginal sex.
Oral Sex with a Man
The risk of HIV transmission through oral sex with a man is very low because the mouth is an unfriendly environment for HIV. Saliva contains enzymes that break down the virus and the mucous membranes in the mouth are more protective than anal or vaginal tissue. There are a few documented cases where it appears that HIV was transmitted orally and those cases are attributed to ejaculation into the mouth.
The minimal risk of transmission from oral sex with a man is only for the person performing the oral sex. Open cuts and abrasions in the mouth or bleeding gums can create an entry point for HIV and increase the risk of transmission. A person receiving oral sex is generally not at risk because that person is coming into contact only with saliva, which does not transmit HIV. The presence of other sexually transmitted infections can increase the risk of HIV transmission during oral sex.
Oral Sex with a Woman
The risk of transmission through oral sex with a woman is very low because the mouth is an unfriendly environment for HIV. Saliva breaks down the virus and the mucous membranes in the mouth are more protective than anal or vaginal tissue. The minimal risk of transmission from oral sex with a woman is only for the person performing the oral sex as their mouth is in contact with vaginal fluid. However, there is little data documenting HIV transmission via oral sex from an infected woman to an uninfected person.
Performing oral sex on a woman who is menstruating increases the risk because blood has more HIV than vaginal fluid. A person receiving oral sex is generally not at risk because that person is coming into contact only with saliva, which does not transmit HIV. The presence of other sexually transmitted infections can increase the risk of HIV transmission during oral sex.
Oral to Anal Sex
Oral to anal contact (rimming) poses minimal risk for HIV transmission. However, rimming is a risk for transmission of hepatitis, parasites, and many other sexually transmitted infections.
HIV can be transmitted by contact between infectious fluids and bleeding cuts or open sores in the skin. However, healthy intact skin does not allow HIV to enter the body and provides an excellent barrier against the virus.
Non-sexual transmission is rare. The rare circumstances where non-sexual transmission has occurred typically involve medical settings or accident scenes where there is a very large volume of blood exposure or a needle stick.
Injection Drug Use
Sharing syringes [including needles and works] poses a very high risk for HIV transmission. Sharing a syringe is the most efficient way to transmit the virus as it passes blood directly from one person's blood stream to another's. Sharing syringes is also a very efficient way to transmit other blood borne viruses such as Hepatitis B and Hepatitis C.
Tattoos and Piercings
There have been no documented cases of transmission of HIV by piercing or tattooing. However, there are documented cases of Hepatitis B transmission. Since Hepatitis B and HIV are transmitted by the same activities, there is a theoretical risk of HIV transmission through tattoos and piercing.
Mother to Infant Transmission
It is possible for a mother who has HIV to pass the virus to her baby by exposure to blood and vaginal fluids during birth or through breast milk during feeding. The risk of transmission from mother to child during pregnancy or birth can be greatly reduced by taking certain HIV medications as prescribed.
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