Contagious: HIV/AIDS

About contagion: Contagion and contagiousness refers to how easily the spread of HIV/AIDS is possible from one person to another. Other words for contagion include "infection", "infectiousness", "transmission" or "transmissability". Contagiousness has nothing to do with genetics or inheriting diseases from parents. For an overview of contagion, see Introduction to Contagion.

Contagion summary: Spread by unprotected sex, oral sex, anal sex, heterosexual sex, blood exposure, transplacental contagion, childbirth transmission, breastfeeding. Not by saliva or kissing. Not by casual contact or touching. Not by clothing, food, or utensils. Not from public toilets or swimming pools. Not by insect bites.

Contagiousness properties of HIV/AIDS:
  Contagious overall?: Yes
  Contagious by sex?: Yes
  Contagious by oral sex?: Yes
  Contagious by anal sex?: Yes
  Contagious by vaginal sex?: Yes
  Contagious from water?: No
  Contagious in swimming pools?: No
  Contagious from food?: No
  Contagious by physical contact (non-sexual)?: No
  Contagious from bedding?: No
  Contagious from clothing?: No
  Contagious from kissing?: No
  Contagious from saliva?: No
  Contagious from surfaces (or objects)?: No
  Contagious from toilet seats?: No
  Contagious from blood?: Yes
  Contagious from blood transfusion?: Yes
  Contagious from intravenous needle usage?: Yes
  Contagious from needlestick injury?: Yes
  Contagious from organ transplant?: Yes
  Contagious from mother to fetus (transplacental)?: Yes
  Contagious mother to baby during childbirth?: Yes
  Contagious breastfeeding mother to infant?: Yes
  Contagious from insect bite (or exposure)?: No

Contagion summary: HIV is spread most commonly by having unprotected sex with an infected partner. The virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex. 1

Transmission of the virus primarily occurs during sexual activity and by sharing needles used to inject intravenous drugs.2

Contagion discussion: Researchers also are studying ways to prevent transmission of HIV from mother to infant. Notably, Pediatric ACTG investigators have demonstrated that a specific regimen of zidovudine (AZT) treatment, given to an HIV-infected woman during pregnancy and to her baby after birth, can reduce maternal transmission of HIV by two-thirds.1 Many consider this finding to be one of the most significant research advances to date in the fight against HIV and AIDS. 3

Almost all HIV-infected children acquire the virus from their mothers before or during birth or through breast-feeding. In the United States, approximately 25 percent of pregnant HIV-infected women not receiving AZT therapy have passed on the virus to their babies. The rate is higher in developing countries. 3

HIV is spread most commonly by having unprotected sex with an infected partner. The virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex.

HIV also is spread through contact with infected blood. Before donated blood was screened for evidence of HIV infection and before heat-treating techniques to destroy HIV in blood products were introduced, HIV was transmitted through transfusions of contaminated blood or blood components. Today, because of blood screening and heat treatment, the risk of getting HIV from such transfusions is extremely small.

HIV frequently is spread among injection drug users by the sharing of needles or syringes contaminated with very small quantities of blood from someone infected with the virus. It is rare, however, for a patient to give HIV to a health care worker or vice-versa by accidental sticks with contaminated needles or other medical instruments.

Women can transmit HIV to their babies during pregnancy or birth. Approximately one-quarter to one-third of all untreated pregnant women infected with HIV will pass the infection to their babies. HIV also can be spread to babies through the breast milk of mothers infected with the virus. If the mother takes the drug AZT during pregnancy, she can reduce significantly the chances that her baby will get be infected with HIV. If health care providers treat mothers with AZT and deliver their babies by cesarean section, the chances of the baby being infected can be reduced to a rate of 1 percent.

A study sponsored by the National Institute of Allergy and Infectious Diseases (NIAID) in Uganda found a highly effective and safe drug regimen for preventing transmission of HIV from an infected mother to her newborn that is more affordable and practical than any other examined to date. Interim results from the study show that a single oral dose of the antiretroviral drug nevirapine (NVP) given to an HIV-infected woman in labor and another to her baby within three days of birth reduces the transmission rate by half compared with a similar short course of AZT.

Although researchers have found HIV in the saliva of infected people, there is no evidence that the virus is spread by contact with saliva. Laboratory studies reveal that saliva has natural properties that limit the power of HIV to infect. Research studies of people infected with HIV have found no evidence that the virus is spread to others through saliva by kissing. No one knows, however, whether so-called "deep" kissing, involving the exchange of large amounts of saliva, or oral intercourse increase the risk of infection. Scientists also have found no evidence that HIV is spread through sweat, tears, urine, or feces.

Studies of families of HIV-infected people have shown clearly that HIV is not spread through casual contact such as the sharing of food utensils, towels and bedding, swimming pools, telephones, or toilet seats. HIV is not spread by biting insects such as mosquitoes or bedbugs.1

Most adolescents recently infected with HIV are exposed to the virus through sexual intercourse, injection drug use, or less often, oral sex. Through June 2000, HIV surveillance data suggest that nearly half of all HIV-infected adolescent males are infected through sex with men. A small percentage of males appear to be exposed by injection drug use and/or heterosexual contact. The same data suggest that almost half of all adolescent females who are infected with HIV were exposed through heterosexual contact and a very small percentage through injection drug use.

CDC studies conducted every two years in high schools (grades nine through 12) consistently indicate that approximately 60 percent of the students have had sexual intercourse by grade 12; half report use of a latex condom during last sexual intercourse, and about one-fifth have had more than four sex partners.

Approximately two-thirds of the 12 million cases of sexually transmitted diseases (STDs) reported in the United States each year are among individuals under the age of 25 and one-quarter are among teenagers. This is particularly significant because if either partner is infected with another STD, the risk of HIV transmission increases substantially. If one of the partners is infected with an STD that causes the discharge of pus and mucus, such as gonorrhea or chlamydia, the risk of HIV transmission is three to five times greater. If one of the partners is infected with an STD that causes ulcers, such as syphilis or genital herpes, the risk of HIV transmission is nine times greater. 4

In the United States, studies have shown that during unprotected heterosexual intercourse with an HIV-infected partner, women have a greater risk of becoming infected than do uninfected men who have heterosexual intercourse with an HIV-infected woman. In other parts of the world, however, this is not necessarily true. In Uganda, for example, one study demonstrated that the risk of HIV transmission from a woman to man was the same as from a man to woman. This difference may be due to the lack of circumcision in Ugandan men.

Studies in both the United States and abroad have demonstrated that STDs, particularly infections that cause ulcerations of the vagina (e.g., genital herpes, syphilis, and chancroid), greatly increase a woman's risk of becoming infected with HIV. NIAID-sponsored cohort studies in the United States have also found a number of other factors to be associated with an increased risk of heterosexual HIV transmission, including alcohol use, history of childhood sexual abuse, current domestic abuse, and use of crack/cocaine.

The consistent and correct use of male latex condoms greatly reduces the risk of becoming infected with HIV. In studies of heterosexual couples, in which one individual was HIV-positive and the other uninfected and regular condom use was reported, the rate of HIV transmission has been extremely low.5

Worldwide, more than 80 percent of all adult HIV infections have resulted from heterosexual intercourse.6

Of new infections among men in the United States, CDC estimates that approximately 60 percent of men were infected through homosexual sex, 25 percent through injection drug use, and 15 percent through heterosexual sex. Of newly infected men, approximately 50 percent are black, 30 percent are white, 20 percent are Hispanic, and a small percentage are members of other racial/ethnic groups.6

Of new infections among women in the United States, CDC estimates that approximately 75 percent of women were infected through heterosexual sex and 25 percent through injection drug use. Of newly infected women, approximately 64 percent are black, 18 percent are white, 18 percent are Hispanic, and a small percentage are members of other racial/ethnic groups.6

A few viruses can pass through breast milk, however. HIV, the virus that causes AIDS, is one of them. Women who are HIV positive should not breastfeed.7

HIV does occur in lesbians, usually due to two factors 1) sharing of needles and 2) when lesbians have sex with men who have been exposed to HIV. However, because there is also a theoretical risk of HIV transmission between lesbians, safe sex guidelines are recommended. Small studies are currently underway to study the risk of HIV infection in lesbians. 8

HIV can be transmitted through the exchange of body fluids (e.g. blood, semen, saliva, and vaginal secretions). HIV is transmittable through all forms of sexual intercourse (oral, vaginal, and anal) when one or both partners are infected with HIV. Oral sex without a latex condom places you at risk of exposure to HIV. It should also be noted that pre-ejaculation fluid can carry HIV and it can be absorbed into the thin mucous linings of the mouth. The Center for Disease Control (CDC) recommends that during oral sex, a latex condom should be used to decrease risk of exposure. 9

There are many myths about HIV/AIDS. The examples below are FACTS:

    You cannot get HIV through casual contact such as shaking hands or hugging a person with HIV/AIDS.

    You cannot get HIV from using a public telephone, drinking fountain, restroom, swimming pool, Jacuzzi, or hot tub.

    You cannot get HIV from sharing a drink or being coughed or sneezed on by a person with HIV/AIDS.

    You cannot get HIV from donating blood.

    You cannot get HIV from a mosquito bite.


1. excerpt from HIV Infection and AIDS, An Overview, NIAID Fact Sheet: NIAID
2. excerpt from Sexually Transmitted Diseases, NIAID Fact Sheet: NIAID
3. excerpt from Backgrounder - HIV Infection in Infants and Children: NIAID
4. excerpt from HIV Infection in Adolescents, NIAID Fact Sheet: NIAID
5. excerpt from HIV Infection in Women, NIAID Fact Sheet: NIAID
6. excerpt from HIV-AIDS Statistics, NIAID Fact Sheet: NIAID
7. excerpt from Breastfeeding: NWHIC
8. excerpt from Lesbian Health: NWHIC
9. excerpt from Women and HIV-AIDS: NWHIC
10. excerpt from HIV, AIDS, and Older People - Age Page - Health Information: NIA

Last revision: April 2, 2003
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