HIV/AIDS: State of Washington Mandatory 4 Hour Training

Part 2. HIV Transmission and Infection Control, Con't.


Part 1. Etiology and Epidemiology of HIV and AIDS

Part 5. Ethical and Legal Issues





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HIV Transmission

People may become infected with HIV if they engage in specific behaviors that put them at risk, or if they are exposed through needlestick injuries (usually in a healthcare setting). Other blood contact with mucous membranes or non-intact skin provides a possible, but not probable, chance of transmission.

HIV is transmitted through:

  • Unprotected anal, vaginal or oral intercourse;
  • Sharing needles or other injection equipment;
  • A mother passing the virus to her baby either before or during birth;
  • An infected woman breastfeeding her infant;
  • Transfusion of HIV-infected blood or blood products (prior to 1986);
  • Accidental needlestick injuries, or infected body fluid coming into contact with the broken skin or mucous membranes of another person (as with healthcare workers);
  • Sharing razors or toothbrushes, if infected blood from one person is deposited on the toothbrush or razor, and the blood enters the bloodstream of another person.

Transmission of HIV occurs primarily through infected blood, semen, vaginal secretions or breast milk. Sweat, tears, saliva, urine and feces are not capable of transmitting HIV unless visibly contaminated with blood. In settings such as hospital operating rooms, other fluids, like cerebrospinal fluid, synovial fluid, pleural fluid, pericardial fluid and amniotic fluid may be considered infectious if the source is HIV positive. These fluids are generally not found outside the hospital setting, so we consider the most common fluids -- blood, semen, vaginal secretions and breast milk -- as infectious in the "real world." Again, outside of the laboratory or medical operation situations, ONLY blood, semen, vaginal fluids and breast milk are considered to be infectious for HIV.

The transmission of HIV depends upon:

  • The availability of the infectious agent in sufficient quantity;
  • The viability of the infectious agent (how strong it is);
  • The virulence of the infectious agent (how infectious it is);
  • The ability of the infectious agent to reach the blood stream, mucous membranes; or broken skin of a potential host (i.e., getting into another person's body).
Case Study #3

Ms. H. is a 20 year old African American female. She has been sexually active since she was 15, and has been treated several times in the past for sexually transmitted diseases (STDs). She recently presented to the STD clinic with c/o painful open sores on her vaginal area. She had several partners in the past two months, but she did not see any similar sores on any of them. The provider told Ms. H that it is important to use barriers when having sex to prevent STDs and also HIV. She explained that it increases the possibility of infection when someone has a break in their skin or mucous membranes, allowing the virus to pass more easily from one person to another. She also explained that, while most STDs can be treated, HIV has no cure. Ms. H. agreed to be tested for HIV as well as STDs. Unfortunately, her test results showed that she had genital herpes, but was negative for HIV. Her provider reminded her that she could have future outbreaks of herpes that would leave her vulnerable to infection with HIV because of the open areas on her skin. She was provided with both male and female condoms before leaving the clinic, and encouraged to tell her partners about the herpes before having sex.

One of the predictors of the infectiousness of someone who is HIV-positive, is their viral load; it indicates how much HIV is present in the bloodstream. Studies show a clear connection between higher viral load in the blood and increased transmissibility of HIV.

Prior to the availability of a test for HIV antibodies, HIV was transmitted by:

  • Artificial insemination;
  • Blood or blood products transfusions;
  • Organ transplants.

Probability of HIV Transmission

The CDC has estimated the following probabilities of infection following ONE exposure to HIV:

  • Contaminated blood transfusion (prior to 1986) 95%

HIV infection rate:

  • One intravenous syringe or needle exposure 0.67%
  • One percutaneous exposure (e.g. a needlestick) 0.4%
  • One episode of receptive anal sexual intercourse 0.1%-3%
  • One episode of receptive vaginal intercourse 0.1%-0.2%
  • One episode of insertive vaginal intercourse 0.03-.09%

A 1% risk means 1 chance in 100 for infection to occur. A 0.10% risk means 1 chance in 1,000.There are no published estimates of the risk for transmission from receptive oral sex or insertive anal sex.

At this time, HIV infection is lifelong, meaning that once a person becomes infected with HIV, their blood, semen, vaginal secretions and/or breast milk will always be potentially infectious.

Sexual Transmission of HIV

HIV can enter the bloodstream through mucous membranes, breaks, sores and cuts in the mouth, anus, vagina or penis. Anal, vaginal and oral intercourse (both receptive and penetrative) can transmit HIV from person to person.

Unprotected anal intercourse is considered to be the greatest sexual risk for transmitting HIV. Anal intercourse frequently results in tears of mucous membranes, which makes it very easy for the virus to enter the bloodstream. The receptive partner ("bottom") is considered to be at more risk of getting HIV, if the virus is present. Risks may vary for the insertive ("top") partner.

Unprotected vaginal intercourse with the exchange of semen, pre-ejaculate fluid (pre-cum), menstrual blood or vaginal fluids is also a risk for HIV transmission. Studies have shown that women are more likely to become infected with HIV through vaginal sex than a man. The larger amount of mucous membrane surface area of the vagina is a probable reason for women's greater rate of HIV infection from their male partners.

Oral sex (mouth to penis, mouth to vagina, mouth to rectum) is considered a risky behavior for HIV transmission because of the exchange of semen, menstrual blood, and/or vaginal fluids that may occur. Studies reported in February 2000 show that oral sex can definitively pass HIV from infected partner to uninfected partner. The person who places their mouth on the partner's genitals is at higher risk for HIV infection than is the "receiving" partner. The actual risk for HIV transmission to persons who are the receptive partner in unprotected oral sex is unclear.

Injecting Drug Use and HIV Transmission

Sharing injection needles, syringes, etc. with an HIV-infected person can put HIV directly into the user's bloodstream and is the behavior which most efficiently transmits HIV, as well as HBV and HCV.

Indirect sharing occurs when drug injectors share injection paraphernalia and/or divide a shared or jointly purchased drug while preparing and injecting it. The paraphernalia that carries the potential for transmission are the syringe, needle, "cooker", cotton, and/or rinse water. Sharing these items (sometimes called "works") may transmit HIV or other bacteria and viruses.

Examples of indirect sharing:

  • Squirting the drug back (from a dirty syringe) into the drug cooker and/or someone else's syringe; and
  • Sharing a common filter and/or rinse water.

HIV and Pregnancy

An HIV-infected woman may transmit the virus to her baby during pregnancy, during the birth process, and/or following pregnancy by breastfeeding. Again, one of the predictors of how infectious the woman will be to her baby is her viral load (how much HIV is present in her bloodstream). Women with new or recent infections, or people in later stages of AIDS tend to have higher viral loads and may be more infectious.

In 1994, researchers discovered that a course of the antiretroviral drug AZT (zidovudine) significantly reduced the transmission of HIV from woman to baby. Since 2002, medications such as AZT and others are used during pregnancy and delivery to prevent transmission of HIV.

Currently, HIV is transmitted from an HIV-infected woman to her baby in about 25% of pregnancies if intervention with antiretroviral medications does not occur. Because of the widespread use of AZT by HIV-infected pregnant women in the U.S., the perinatal transmission rate has dropped dramatically. When a woman's healthcare is monitored closely and she receives a combination of antiretroviral therapies during pregnancy the risk of HIV transmission to the newborn drops to below 2%. In some pregnancies, caesarian section (C-section) may be recommended to reduce the risk of transmission from woman to baby. Advice about medications and C-section should be given on a case-by-case basis by a healthcare provider with experience in treating HIV positive pregnant women.

Washington state law requires pregnant women to be counseled regarding risks around HIV and offered voluntary HIV testing.

Transfusions of Blood or Blood Products

In 1999 only 1% of national AIDS cases were caused by transfusions or use of contaminated blood products. The majority of those cases were in people who received blood or blood products before 1985. Testing for HIV began in 1985 and has almost completely eliminated this risk for transmission in developed countries.

Upon recognizing that HIV could contaminate the blood supply, government scientists sought ways to keep it safe.

Courtesy of National Institutes of Health.

Donor screening, blood testing and other processing measures have reduced the risk of transfusion-caused HIV transmission to between 1 in 450,000 to 1 case in 600,000 transfusions in the U.S. In the U.S., donating blood is always safe, because sterile needles and equipment are used.

Transmission of Multi- Drug Resistant Forms of HIV

There is evidence of transmission of multi-drug resistant forms of HIV. People who have been infected with HIV and have used a number of the available antiretroviral medicines may transmit forms of HIV that are resistant to some of these available drug therapies. This reduces the treatments available for the newly-HIV-infected person. It is believed that inconsistent use of antiretroviral medications can contribute to this multi-drug resistant HIV.

Continue to Part 2. HIV Transmission and Infection Control, Con't.