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AIDS and HIV Infection Facts

How HIV is transmitted

To date, there are only four primary methods of transmission:

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Basic Facts about HIV prevention

Sexual intercourse

HIV can be transmitted through unprotected sexual intercourse -that is, any penetrative sexual act in which a condom is not used. Anal and vaginal intercourse can transmit the virus from an HIV-infected man to a woman or to another man, or from an infected woman to a man.

The risk of becoming infected through unprotected sexual intercourse depends on four main factors:

Age may also be a factor as young girls are physiologically more vulnerable.

The probability of HIV infection in the partner

The prevalence of HIV infection among sexually active men and women varies according to geographical area or population subgroup, such as heterosexuals, men who have sex with men (MSM), sex workers, or injecting drug users. Generally, the likelihood of becoming infected with HIV sexually is related to the number of sexual partners and unprotected sex acts you have. In other words, the more sexual partners you have, the greater your chance of becoming infected.

The type of sex act

All unprotected acts of sexual penetration (anal, vaginal, oral) carry a risk of HIV transmission because they bring body fluids secreted during sex directly into contact with exposed mucous membranes (the lining of the rectum, the vagina, the urethra and the mouth).

The amount of virus present in the infected partner

HIV-infected individuals become more infectious as they progress to HIV-related disease and AIDS. There is also an early one- to two-week period of infectiousness around the time of seroconversion—that is, when antibodies first develop.

The presence of other sexually transmitted diseases in either partner There is a strong link between sexually transmitted diseases (STDs) and the sexual transmission of HIV infection. The presence of an untreated STD—such as gonorrhoea, chlamydial infection, syphilis, herpes or genital warts—can enhance both the acquisition and transmission of HIV by a factor of up to 10. Thus, STD treatment is an important HIV prevention strategy in a general population.

Contaminated blood and blood products, tissues and organs

Blood transfusions save millions of lives each year, but in places where a safe blood supply is not guaranteed, those receiving transfused blood have an increased risk of being infected with HIV.

In most industrialized countries, the risk of acquiring HIV infection from transfusions is extremely low. This is due in large part to effective recruitment of regular, volunteer blood donors; improved donor testing procedures; universal screening of blood and blood products with highly sensitive and specific tests for the antibody to HIV; and the appropriate use of blood.

In the developing world, however, the risk is much higher. One estimate is that up to 5 percent of HIV infections may be caused by transfusions in high-prevalence areas such as sub-Saharan Africa. The lack of coordinated national blood transfusion systems, the absence of non-remunerated volunteer blood donors, lack of testing, and inappropriate use of blood products compound the problem.

To prevent transmission by tissue and organ donation, including sperm for artificial insemination, the HIV-infection status of the donor should be carefully evaluated.

Contaminated needles, syringes or other piercing instruments

HIV can be transmitted through the use of HIV-contaminated needles or other invasive instruments. The sharing of syringes and needles by injecting drug users is responsible for the very rapid rise in HIV infection among these persons in many parts of the world.

A risk is also attached to non-medical procedures if the instruments used are not properly sterilized. Such procedures include ear- and body-piercing, tattooing, acupuncture, male and female circumcision, and traditional scarification. The actual risk depends on the local prevalence of HIV infection.

HIV transmission by means of injection equipment can also occur in health care settings where syringes, needles and other instruments, such as dental equipment, are not properly sterilized, or through injury by needles and other sharps.

Mother-to-child transmission (MTCT)

Mother-to-child transmission (MTCT) is the overwhelming source of HIV infection in young children. The virus may be transmitted during pregnancy, labour, and delivery or after the child's birth during breastfeeding. Among infected infants who are not breastfed, most MTCT occurs around the time of delivery (just before or during labour and delivery). In populations where breastfeeding is the norm, breastfeeding may account for more than one-third of all cases of MTCT transmission.

Paediatric AIDS can be difficult to diagnose because some symptoms of HIV infection, such as diarrhoea, are also common in infants and children who are not infected. Therefore, these symptoms cannot be considered a reliable basis for diagnosis. There are blood-based tests: for example, ELISA which is reliable only at 15 months of age, and PCR tests that allow early diagnosis, but these tests are quite expensive and are not readily available in developing countries.

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