Most commonly, HIV infection is spread by having sex with an infected partner. The virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex. Although initially AIDS cases occurred primarily in homosexual males in the United States, more recently the majority of new cases are in the heterosexual population.
- HIV also spreads through contact with infected blood through a transfusion of contaminated blood or blood components.
- HIV frequently spreads among injection drug users who share needles or syringes that are contaminated with blood from an infected person.
- Women can transmit HIV to their babies during pregnancy or birth.
- The virus does not spread through casual contact such as sharing of food, utensils, towels and bedding, swimming pools, telephones, or toilet seats. The virus is also unlikely to be spread by contact with saliva.
- People who already have a sexually transmitted disease, such as syphilis, genital herpes, chlamydial infection, gonorrhea, or bacterial vaginosis, are more likely to acquire HIV infection during sex with an infected partner.