HIV is primarily a sexually transmitted disease but can be contracted in three ways.  All require the exchange of bodily fluids, such as semen, blood, breast milk, or vaginal secretion. 

Sexual Transmission

The majority of HIV cases are acquired through unprotected sexual encounters.  The sexual secretion of an infected person can come into contact with the genital, oral, or rectal mucous membrane of another and affect the uninfected partner.  Both heterosexual and homosexual encounters can cause infection, with higher risk to the receptive partner. Anal intercourse has a higher risk of transmitting HIV than vaginal intercourse.

Blood Products

The most common cases of blood transmission of the disease occur primarily amongst intravenous drug users, hemophiliacs, and recipients of blood transfusion.  Sharing or reusing syringes contaminated with infected blood poses a great risk for contracting the virus.  Receiving tattoos with infected needles can also expose participants to the virus.  In regions with substandard medical hygiene, the risk of acquiring HIV through blood is much higher than in more sterile medical environments.

Perinatal Transmission

The transmission of the disease from mother to child can happen at any point during the childbearing process.  It can occur to the fetus in-utero, through an exchange of bodily fluids through the umbilical chord.  It can also occur during childbirth, through the exchange of bodily fluids.  This can be largely avoided through birth by caesarean section, so fluids are kept separate.  Lastly, transmission can occur during breast-feeding as the child consumes the infected mother’s breast milk.