Hiv Aids

Transmission of Infection

The transmission of HIV requires contact with a body fluid that contains the virus or infected cells. HIV can appear in nearly any body fluid, but transmission occurs mainly through blood, semen, vaginal secretions, and breast milk. Although tears, urine, and saliva may contain low concentrations of HIV, transmission through these fluids is extremely rare, if it occurs at all. HIV is not transmitted by casual contact (such as touching, holding, or dry kissing) or by close, nonsexual contact at work, school, or home. No case of HIV transmission has been traced to the coughing or sneezing of an infected person or to a mosquito bite. Transmission from an infected doctor or dentist to a patient is extremely rare.

HIV is transmitted in the following ways:

sexual contact with an infected person, when the mucous membrane lining the mouth, vagina, penis, or rectum is exposed to contaminated body fluids (as occurs during unprotected sexual intercourse)

injection or infusion of contaminated blood, as can occur with blood transfusions, the sharing of needles, or an accidental prick with an HIV-contaminated needle

transfer from an infected mother to a child before birth, during birth, or after birth through the mother's milk

Susceptibility to HIV infection increases when the skin or a mucous membrane is torn or damaged—even minimally—as can happen during vigorous vaginal or anal sexual intercourse. Sexual transmission of HIV is more likely if either partner has herpes, syphilis, or another sexually transmitted disease (STD) that causes breaks in the skin or inflammation of the genitals. However, HIV can be transmitted even if neither partner has another STD or obvious breaks in the skin. HIV transmission can also occur during oral sex, although it is less common than during vaginal or anal intercourse.

In the United States, Europe, and Australia, HIV has mainly been transmitted through male homosexual contact and the sharing of needles among injecting drug users, but transmission through heterosexual contact has been rapidly increasing. HIV transmission in Africa, the Caribbean, and Asia occurs primarily between heterosexuals, and HIV infection occurs equally among men and women. In the United States, about 30% of adults who have HIV infection are women. Before 1992, most American women with HIV were infected by injecting drugs with contaminated needles, but now most are infected through sexual contact.

When people are first infected, symptoms of fever, rashes, swollen lymph nodes, and fatigue may last a few days to several weeks.

Many infected people remain well for more than a decade, but within about 10 years, about half of people become ill and develop AIDS, defined by the presence of serious