Gerald Hurowitz, M.D.·Published 18 April 2005·14 min read
Key points
Scientific research shows that the human immunodeficiency virus (HIV) is transmitted by contaminated body fluids such as blood, semen (including pre-ejaculatory fluid), vaginal fluids and breast milk.
French kissing when no blood is present (saliva is not a body fluid that can transmit HIV) masturbating (oneself or someone else) using a sex toy and not sharing it.
These acts present a risk of HIV transmission because they lead to an exchange of body fluids that can transmit HIV.
Earlier studies attempted to estimate the rate of HIV transmission, but were typically quite small, and did not measure the concentration of the virus in the blood throughout the entire study period.
Scientific research shows that the human immunodeficiency virus (HIV) is transmitted by contaminated body fluids such as blood, semen (including pre-ejaculatory fluid), vaginal fluids and breast milk. Unprotected sex is one of the leading modes of transmission.
A heterosexual person infected with HIV will transmit the virus to their partner once in every 900 times the couple has unprotected sex, according to a new study conducted in Africa.
However, the exact number of sexual acts that are needed to transmit the virus can vary tremendously depending on the amount of the virus in the infected person's blood, said study researcher James Hughes, of the University of Washington in Seattle.
In fact, the amount of virus in the blood is the single most important factor in determining whether HIV is passed between sexual partners, the study found. For every tenfold increase in the concentration, there is about a threefold increase in the risk of transmission during a single sexual act.
People with very high blood concentrations of the virus (such as those who very recently acquired the infection) may need to have sex only 10 times to transmit the virus, Hughes said. "The average can be a little deceptive," Hughes said.
The new findings reinforce the idea that the best methods for reducing HIV transmission are those that decrease the concentration of the virus in the blood, as can be done with antiretroviral drugs, Hughes said. A study published last year found the drugs could reduce the transmission of HIV between partners by 96 percent.
No risk
These are acts that present no risk of HIV transmission because there is no exchange of body fluids and no transmission of HIV has been documented:
French kissing when no blood is present (saliva is not a body fluid that can transmit HIV) masturbating (oneself or someone else) using a sex toy and not sharing it.
The new study also confirmed condoms are highly effective in preventing HIV infection, reducing the risk of transmission by 78 percent. Male circumcision reduced the risk of HIV transmission by 47 percent.
Low risk
These acts present a risk of HIV transmission because they lead to an exchange of body fluids that can transmit HIV. Infection cases have been documented for acts like:
fellatio given without a condom (when semen or pre-ejaculatory fluid is present) cunnilingus given without protection (whether during menstruation or not) vaginal penetration with a condom (risk exists for both partners)
Written and revised by
Gerald Hurowitz, M.D.
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anal penetration with a condom (risk exists for both partners).
French kissing when blood is present.
HIV transmission
Earlier studies attempted to estimate the rate of HIV transmission, but were typically quite small, and did not measure the concentration of the virus in the blood throughout the entire study period.
Sexual intercourse with an HIV-infected person
HIV infection is sexually transmitted primarily through unprotected vaginal or anal intercourse (i.e. sexual intercourse without a condom), as well as through oral sex under certain conditions.
How does HIV get into the body during sexual contact?
To gain entry into the body of an uninfected person, the HI virus needs to bind or "latch onto" target cells with specific receptors (namely CD4 receptors) on its surface. Cells with these special receptors are plentiful in the lining of the genital track and that of the anus.
During unprotected sex with an HIV+ person, the virus (in the sexual fluids of the infected person) binds with the CD4 receptors in the lining of the genital tracks (e.g. vagina) or anal track of the uninfected partner.
Tears (often microscopically small) in the membrane linings of the genital tracks - especially in the anal-rectal area - also make it easy for the virus to enter the sex partner's bloodstream. Because the membrane linings of body cavities - especially in the anal-rectal area, and, to a lesser extent, in the vagina - are very delicate, they can be torn as a result of friction generated during sexual intercourse. (Rough sex, dry sex and forced sex or rape often lead to friction, tears and bleeding.)
Sexually transmitted infections (STIs), such as syphilis, gonorrhoea or herpes, make it very easy for HIV to get into the body. An untreated STI in either partner increases the risk of HIV transmission during unprotected intercourse ten-fold.
People with genital herpes or genital ulcers or sores are especially susceptible to HIV infection because these conditions create openings in the linings of the genital tracks through which HIV can move. The discharges produced by many STIs contain a very high concentration of HIV if that person is also HIV positive.
The new study included 3,297 couples from sub-Saharan Africa that were "HIV-discordant," meaning one partner had HIV while the other did not. The HIV-infected partners in the study were tested periodically over the two-year study for the amount of HIV in their blood. Infected partners were also interviewed every month and asked how many times they had sex, and whether they used protection.
Are there risks of getting HIV if I drink or use drugs?
Yes! Alcohol or drugs won't infect you with HIV, but taking risks while you're drunk or high might.
When you drink or use drugs, you may not make the same decisions as you would when not under the influence. For example, you may not bother to use protection during sex. Having unprotected sex is a common way of getting HIV.
You may also take the risk of sharing a needle to inject drugs. About one quarter of all new HIV infections occur among people who inject drugs. This is due to the invisible amount of blood that is in the needle or syringe or other injection equipment such as cookers, water, cotton filters, straws and pipes. If you use the same needle as someone who is infected with HIV, you shoot her/his infected blood into your bloodstream.
Remember that poppers (nitrite inhalants) and erectile dysfunction medications increase blood flow by dilating the blood vessels in the pelvic area, making the skin of the vagina and anus thinner and weaker, and therefore easier to tear. Tiny tears in these tissues make it easier for viruses to enter your bloodstream, increasing your risk for HIV infection.
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The uninfected partners were tested periodically to see whether they had acquired HIV. The researchers used genetic testing of the virus to confirm that any new HIV infections had been acquired from the study partner designated at the study's start.
Eighty-sixHIV transmissions occurred during the study period.
Men were about twice as likely to transmit HIV to women as women were to men. This increased risk of transmission could be attributed to higher virus concentrations in the blood of men compared with women, according to the study. In addition, women were more likely to have genital herpes, which increases susceptibility to HIV.
Why are women more easily infected by HIV than men? Women are two to four times more likely to get infected with HIV through unprotected vaginal sex than men, due to the following reasons:
Women, as the recipients of semen, are exposed to semen for a longer time (while semen remains in the body of a woman for a few hours, a man is exposed to the body fluids of a woman for only a short time);
The concentration of HIV in semen is much higher than the concentration of HIV in vaginal fluids;
Women possess a larger surface area of mucosa (the thin lining of the vagina and cervix) which is exposed to their partner's secretions during sexual intercourse;
Many women have cervical or vaginal conditions, such as STIs, erosions, open sores and infections, that facilitate the transmission of HIV;
Many women practise "dry" sex and they cause damage or infection to the vaginal walls ("dry" sex is a cultural practice where women use herbs or other substances - such as Jik or washing powder - to dry out their vaginas for the benefit of some men who believe that a dry vagina is a sign of faithfulness, or to heighten their sexual pleasure.) This practice is painful and extremely dangerous because it increases the risk of HIV infection;
Transmission of HIV is more likely to occur just before, during or immediately after menstruation because of the large, raw area of the inner uterine lining that is exposed;
Younger women are especially vulnerable to HIV infection because their genital tracts are not yet fully mature, their vaginal secretions are not so copious, and because they are more prone to lacerations or tears of the vaginal lining. (There is also evidence to suggest that women once again become more vulnerable to HIV infection after menopause).
Women often practice anal sex to avoid pregnancy, to maintain "virginity", or because their male partners prefer anal sex for reasons similar to the reasons why they prefer "dry sex". Research has shown that the chances to become infected with HIV after one act of unprotected receptive anal sex is approximately 20 times greater than after one act of unprotected vaginal sex.
Social inequalities often make women more vulnerable to HIV infection especially in societies which accord women a lower status than men. Women in such situations have little or no control over their sex lives, and they are not in a position to negotiate safer sex practices because they fear violence and abandonment should they try to do so. Women from low socio-economic environments are often driven to prostitution, and they are particularly vulnerable to rape.
Condoms were reported to be used in 93 percent of sexual acts, but the researchers suspect their use was overreported. Therefore, condoms actually may be even more effective at preventing HIV transmission than the 78 percent reduction that the researchers estimated, Hughes said.
The AIDS epidemic
The study relied on self-reports, which might be wrong. However, errors in reports of the number of sexual acts would be unlikely to affect most of the study results, Hughes said.
HIV infection is best characterized as a sexually transmitted disease (STD). In the United States, ∼75% of HIV-infected individuals acquired the virus through sexual activity. It is estimated that, in other areas of the world, >90% of new infections among adults are acquired via sexual activity. Effective methods to prevent sexual transmission of HIV are critical to the effort to defeat the worldwide epidemic. Although injection drug use continues to be an important source of transmission in the United States (it ranks second, after sexual activity), other avenues of acquiring infection, including vertical transmission from mother to child and use of HIV-contaminated blood products, are of diminishing importance.
In the United States, male-male sex is the avenue of HIV transmission in ∼60% of new cases. Heterosexual contact, although accounting for only ∼17.5% of new infections, is the mode of HIV transmission in 80% of new cases in women. From 2000 through 2003, the estimated number of HIV/AIDS cases increased by 5% among males and decreased by 2% among females. In 2003, a total of 72% of all HIV/AIDS cases were diagnosed in men or adolescent boys . The difference in the HIV infection rate between men and women in the United States, which has persisted since the start of the epidemic, may be best understood in the context of the efficiency of different routes of HIV transmission, particularly the relative rates of transmission via vaginal and anal intercourse.
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How does HIV get into the body during sexual contact?
To gain entry into the body of an uninfected person, the HI virus needs to bind or "latch onto" target cells with specific receptors (namely CD4 receptors) on its surface. Cells with these special receptors are plentiful in the lining of the genital track and that of the anus.
During unprotected sex with an HIV+ person, the virus (in the sexual fluids of the infected person) binds with the CD4 receptors in the lining of the genital tracks (e.g. vagina) or anal track of the uninfected partner.
Tears (often microscopically small) in the membrane linings of the genital tracks - especially in the anal-rectal area - also make it easy for the virus to enter the sex partner's bloodstream. Because the membrane linings of body cavities - especially in the anal-rectal area, and, to a lesser extent, in the vagina - are very delicate, they can be torn as a result of friction generated during sexual intercourse. (Rough sex, dry sex and forced sex or rape often lead to friction, tears and bleeding.)
Sexually transmitted infections (STIs), such as syphilis, gonorrhoea or herpes, make it very easy for HIV to get into the body. An untreated STI in either partner increases the risk of HIV transmission during unprotected intercourse ten-fold.
People with genital herpes or genital ulcers or sores are especially susceptible to HIV infection because these conditions create openings in the linings of the genital tracks through which HIV can move. The discharges produced by many STIs contain a very high concentration of HIV if that person is also HIV positive.
How many sexual contacts with an HIV-positive person are necessary before one becomes infected oneself? It is impossible to say how many sexual contacts with an infected partner/s are necessary before an HIV-negative person becomes HIV-positive.
HIV transmission from one person to another through sexual contact can depend on any of the following factors:
Unprotected (without a condom) sex with multiple sex partners.
The presence of other STIs (sexually transmitted infections), especially in the case of genital ulcers and inflammatory STIs.
Trauma (or bleeding) during sex, as well as menstruation.
The viral concentration (or level of viral "load") in the blood of the infected partner.
The level of viral load in the semen or vaginal fluids of the infected partner (Viral load in semen peaks three weeks after infection. HIV is 20 times more transmissible per sex act, at this stage.)
The phase of infection. HIV is much more contagious in the acute infection phase (first eight to 12 weeks after infection) as well as in the final phases when advanced disease (or Aids) has set in. The reason why HIV is easier transmitted during these phases, is because the viral load is especially high in the acute infection phase, and again in the final phase of Aids.
When the immune system is suppressed (this is also then an indication of a high viral load and a low CD4 count.
Other diseases such as malaria. The HIV viral load is very high in people who also have malaria.
HIV-1 subtype C is more infectious than other subtypes, and subtype C is unfortunately the viral subtype that occurs in South Africa.
Is it true that circumcision can protect males against HIV infection? Several studies reported at the Aids conference in Barcelona (2002) indicated that circumcision can indeed reduce the risk of HIV infection for the circumcised male, but:
It seems that circumcision only provides a measure of protection if the circumcision was done before the boy reached puberty (cancel those appointments men!)
The direction of effectivity is not clear yet (in other words, will male circumcision also lower the risk of male to female transmission - and protect the sex partner?)
If the circumcision procedure is done with unsterilised, dirty blades (or other instruments) - as often happens in Africa - HIV-infected blood could pass from one boy (or male) to another.
Although circumcision may lower the risk of HIV infection in circumcised men, circumcision should definitely not be promoted as the only way of preventing HIV infection! Safer sex practices such as the use of condoms should always be practised, disregarding circumcision or not!
If I am HIV+, why should I still use a condom to protect myself? HIV+ individuals still need to protect themselves against re-infections with HIV, for the following reasons:
Each new infection can cause an increase in the viral load in the blood and
The person can become infected with a new strain of the virus. It is therefore important for HIV+ people to protect themselves from re-infection by always using condoms.
Can lesbians get Aids? Yes, lesbian women can also get Aids.
Lesbians who have sex with women as well as men, can contract HIV infection if they have sex with infected men.
Although the risk of HIV-infection is small for women who have sex exclusively with other women, lesbian women can contract HIV infection by sharing contaminated sex toys (e.g. vibrators or dildo's) for vaginal or anal penetration. Because sex toys can cause bleeding or irritation of the vaginal or anal lining, it is easier for the HI virus to enter the body if people use them or share them. When sex toys are used, they should be thoroughly cleaned and preferably not shared, but if they are shared, the sex toy should be covered with a condom (a new condom for each partner!).
It should also be kept in mind that menstruation blood of an HIV+ woman is contagious. A plastic/latex cover such as "glad wrap", a dental dam, or a condom that is cut open, should be placed over the vagina for oral sex (also for heterosexual oral sex with a woman).
### Myron S. Cohen
Dr. Myron S. Cohen, University of North Carolina School of Medicine, CB #7030, 130 Mason Farm Rd., 4123 Bioinformatics Bldg., Chapel Hill, NC 27599-7030 (mscohen@med.unc.edu). Presented in part: Opportunities for Improving HIV Diagnosis, Prevention & Access to Care in the U.S., Washington, D.C., 29–30 November 2006.
The average risk of HIV infection per sexual act estimated in the study is consistent with what has been found by previous research, but there are many situations in which that number may not apply," said Dr. Myron Cohen, a professor of medicine, microbiology, immunology and public health at the University of North Carolina at Chapel Hill, who was not involved in the work.
That's because the participants included in the study are couples that have remained together and discordant over a long period of time. This indicates the couples might have some biological protection against transmission, Cohen said.
"The true estimation might be higher if you were studying different kinds of people," Cohen said.
While most of the findings are likely generalizable to other countries, the number of sexual acts needed to transmit the virus is likely specific to the African population studied, Hughes said. Previous studies in the United States have found a lower transmission rate.
In addition, the findings only apply to heterosexual couples, and not men who have sex with men, a group that is likely to have a much higher transmission rate, Hughes said.
Pass it on: The best way to reduce the risk of HIV transmission is to lower the amount of the virus in the blood.
###
Cameron DW, Simonsen JN, D'Costa LJ, et al
. Female to male transmission of human immunodeficiency virus type 1: risk factors for seroconversion in men.
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