Introduction
Human immunodeficiency virus (HIV) was established to be the cause of the acquired immunodeficiency syndrome (AIDS) in 1983. Ever since then, a lot of research has been conducted and a great deal of information has been generated regarding the ways HIV can be transmitted from one person to another.
The problem with much of the information about HIV transmission, especially on the World Wide Web, is that it speaks in very general terms. All too often, there is a lot of conflicting information as well. For example, some sources refer to oral sex as "risky," whereas others say "low risk" or "no risk." This can be very frustrating and it also leads to the spread of misinformation about the transmission of HIV.
HIV infection – and HIV testing – is a medical issue. We have developed this lesson to provide straightforward and accurate information regarding HIV transmission. However, it is important to stress that this lesson – and other sources of HIV information on the World Wide Web – should not be consulted as an alternative to medical care and testing. If you fear that you have been exposed to HIV – regardless of how low the perceived risk and no matter how much information you find on the World Wide Web – you need to get in touch with your healthcare provider or an HIV testing center.
How is HIV Transmitted?
HIV enters the body through open cuts, sores, or breaks in the skin; through mucous membranes, such as those inside the anus or vagina; or through direct injection. There are several ways by which this can happen:
 |
Sexual contact with an infected person. This is the primary focus of this lesson and is reviewed in greater detail in the following sections.
|
|
Sharing needles, syringes, or other injection equipment with someone who is infected.
|
|
Mother-to-child transmission. Babies born to HIV-positive women can be infected with the virus before or during birth, or through breastfeeding after birth. More information about HIV and pregnancy can be found in this lesson.
|
|
Transmission in healthcare settings. Healthcare professionals have been infected with HIV in the workplace, usually after being stuck with needles or sharp objects containing HIV-infected blood. As for HIV-positive healthcare providers infecting their patients, there have only been six documented cases, all involving the same HIV-positive dentist in the 1980s.
|
|
Transmission via donated blood or blood clotting factors. However, this is now very rare in countries where blood is screened for HIV antibodies, including in the United States. |
Since the beginning of the HIV/AIDS epidemic, new or potentially unknown routes of transmission have been thoroughly investigated by state and local health departments, in collaboration with the U.S. Centers for Disease Control and Prevention (CDC). To date, no additional routes of transmission have been recorded, despite a national system designed to detect unusual cases.
Sexual Transmission of HIV
In the United States, sexual contact is the most common route of HIV transmission. As of December 2004, 44% of AIDS cases reported to the CDC were among men who contracted HIV through sex with other men (MSM). The term MSM is important – and used quite a bit in this lesson – because many men who have sex with men do not necessarily identify themselves as "gay" or even "bisexual." HIV transmitted through sexual activity among heterosexuals accounted for 13% of all AIDS cases reported to the CDC, with most of these cases among women infected by men. Only a small percentage (less than 5%) of AIDS cases in the United States involves men who were infected with HIV through sexual activity with HIV-positive women.
Heterosexual intercourse is the most common mode of HIV transmission in poor countries. In Africa slightly more than 80% of infections are acquired heterosexually, while mother-to-child transmission and transfusions of contaminated blood account for the remaining infections. In Latin America, most infections are acquired through MSM and through misuse of injected drugs, but heterosexual transmission is rising. Heterosexual contact and injection of drugs are the main modes of HIV transmission in South and South East Asia.
The reason why sexual activity is a risk for HIV transmission is because it allows for the exchange of body fluids. Researchers have consistently found that HIV can be transmitted via blood, semen, and vaginal secretions. It is also true that HIV has been detected in saliva, tears, and urine. However, HIV in these fluids is only found in extremely low concentrations. What's more, there hasn't been a single case of HIV transmission through these fluids reported to the CDC.
Specific Sexual Practices: What are the Risks?
Studies have repeatedly demonstrated that certain sexual practices are associated with a higher risk of HIV transmission than others.
Vaginal Intercourse:
Unprotected vaginal intercourse is the most common mode of HIV infection worldwide. In the United States and many other developed nations, it is the second most common mode of sexual HIV transmission (after anal intercourse among MSM).
At least five European and American studies have consistently demonstrated that male-to-female HIV transmission during vaginal intercourse is significantly more likely than female-to-male HIV transmission. In other words, HIV-positive men are much more likely to transmit the virus to HIV-negative women through vaginal intercourse than HIV-positive women are to HIV-negative men.
There are a few reasons for this. First, there are more men than women in the United States infected with HIV, meaning that it's much more likely for a female to have sex with an HIV-positive male than for a male to have sex with an HIV-positive female. Second, women have a much larger surface area of mucosal tissue – the lining of the vagina and cervix that can chafe easily and are rich in immune system cells that can be infected by HIV – than men. For men, HIV must enter through a cut or abrasion on the penis, through the lining of the urethra inside the penis.
There has been some research suggesting that men who are uncircumcised have a higher risk of becoming infected with HIV or transmitting the virus if they are already HIV positive. However, it is important to stress that men who are circumcised can still be infected (or transmit the virus) if condoms are not used for vaginal sex.
Men or women who have ulcerative sexually transmitted infections (STIs), such as genital herpes or syphilis, are more likely to spread the virus if they are HIV positive or to become infected with the virus if they are HIV negative.
Anal Intercourse:
Being the receptive partner – the "bottom" – during unprotected anal intercourse is linked to a high risk of HIV infection. The reason for this is that HIV-infected semen can come into contact with mucosal tissues in the anus that can be damaged easily during anal intercourse. And the risk of HIV transmission isn't necessarily reduced if the "top" pulls out before ejaculation – studies have demonstrated that pre-ejaculate (pre-cum) can contain high amounts of HIV and can result in transmission during anal intercourse.
It's important to note that both MSM and heterosexuals have anal intercourse. Many heterosexuals report that it is a pleasurable form of intimacy that eliminates the risk of pregnancy. However, it is still associated with a high risk of HIV infection, if condoms are not used and the insertive partner's HIV status is either positive or not known.
Is the insertive partner (the "top") also at risk during unprotected anal intercourse? At least eight studies conducted over the years were unable to demonstrate a clear link between insertive anal sex and a risk for HIV infection among MSM. However, these studies should not be interpreted to mean that being the top during anal intercourse – and not using a condom – is without risk. We know that men can be infected with HIV through vaginal intercourse – an activity in which they are the insertive partner. Based on this knowledge, it is also believed that the insertive partner during unprotected anal intercourse can also be infected with HIV. Studies, using mathematical estimates, suggest that unprotected insertive anal sex is roughly four to 14 times less risky than unprotected receptive anal sex. However, experts still believe that the risk for transmission is noteworthy.
Penile-Oral Sex
Of the different sex acts, the one that often causes the greatest amount of confusion in terms of risk – and raises the greatest number of questions – is penile-oral sex. The fact is, most experts agree that fellatio, sometimes referred to as "blow jobs," is not an efficient route of HIV transmission. However, this does not mean that it cannot happen.
Research attempting to evaluate the risk of fellatio has often faced important limitations. For starters, very few people participating in studies only engaged in penile-oral sex. Many people also had unprotected vaginal or anal intercourse, making it very difficult to determine if unprotected fellatio is an "independent factor" associated with HIV transmission. There are also people who test positive for HIV and claim that unprotected fellatio was their only risky behavior. However, it's virtually impossible to know if these people are always reporting their sexual behavior accurately. (Study volunteers often have a difficult time admitting the truth about potentially embarrassing behavior to healthcare professionals conducting scientific studies.)
Because unprotected fellatio can mean that body fluids from one person can (and do) come into contact with the mucosal tissues or open cuts, sores, or breaks in the skin of another person, there is a "theoretical risk" of HIV transmission. "Theoretical risk" means that passing an infection from one person to another is considered possible, even though there haven't been any (or only a few) documented cases. This term can be used to differentiate from documented risks. Having unprotected receptive anal or vaginal intercourse with an HIV-positive partner is a documented risk, as they have been shown in numerous studies to be an independent risk factor for HIV infection. Having unprotected oral sex is a theoretical risk, as it is considered possible, but has never been shown to be an independent risk factor for HIV infection.
Here's a good way to think about theoretical risk: In theory, it is possible that while walking down the street, a meteor will fall on your head and kill you instantly. This is because meteors do occasionally fall to earth. People live their lives above ground, so there is a theoretical risk of being hit be a meteor. In fact, there have been reports of a few people being hit by meteors. But because the risk is so small, given that few meteors fall to earth and the large number of inhabitants of this planet, the risk is purely theoretical. The same principle holds true with oral sex – millions of people all over the world are believed to engage in unprotected oral sex and there have only been a handful of documented cases of HIV transmission. In turn, fellatio, and other types of oral sex (see below), remains a theoretical risk for HIV infection.
There have been a number of studies that have closely followed MSM and heterosexual couples, in which one partner was HIV positive and the other partner was HIV negative. In all of the studies, couples that used condoms consistently and correctly during every experience of vaginal or anal sex – but didn't use condoms during oral sex – did not see HIV spread from the HIV positive partner to the HIV negative partner.
There have been three case reports and a few studies suggesting that some people have been infected with HIV as a result of unprotected oral sex. However, these case reports and studies all involved MSM – men who were the receptive partners (the person doing the "sucking") during unprotected oral sex with another HIV-positive man. There haven't been any case reports or studies documenting HIV infection among female receptive partners during unprotected oral sex. Even more importantly, there hasn't been a single documented case of HIV transmission to an insertive partner (the person being "sucked") during unprotected oral sex, either among MSM or heterosexuals.
Is insertive oral sex a possible route of HIV transmission? Yes. But is it a documented risk? Absolutely not.
Oral-Vaginal Sex
Like the study of fellatio, evaluating the risk of unprotected oral-vaginal sex (cunnilingus) is difficult, given that most people surveyed in studies did not avoid other types of unsafe sexual activity. However, there have been case reports highlighting one case of female-to-female transmission of HIV via cunnilingus and another case of female-to-male transmission of HIV via cunnilingus. Both of these cases involved transmission from receptive partner (the one receiving oral sex) to the insertive partner (the one performing oral sex). There haven't been any documented cases of HIV transmission from the insertive partner to the receptive partner.
Oral-Anal Sex
Oral-anal sex is often referred to as analingus. Analingus, or "rimming," is not considered to be an independent risk factor for HIV. However, it has been shown to be a route of transmission for hepatitis A and B, as well as parasitic infections like giardiasis and amebiasis.
Digital-Anal or Digital-Vaginal Sex
Digital-anal or digital-vaginal sex is the clinical term for "fingering" either the anus or the female genitals (including the vagina). While it is theoretically possible that someone who has an open cut or fresh abrasion on his or her finger or hand can be infected with HIV if coming into contact with blood in the anus or vagina or vaginal secretions, there has never been a documented case of HIV transmission via fingering.
What about the "per-act risk" numbers?
Epidemiologists – scientists who study the transmission and control of epidemic diseases – are fond of using mathematical models to calculate the risks of certain infections spreading (like HIV) from person to person. These calculations are usually written as the "per-act" or "per-contact" risk. For example, one study conducted by the CDC – and frequently cited by many sources of HIV transmission information – suggested that a person has a 1 in 200 chance of becoming infected with HIV if he is the receptive partner during unprotected anal intercourse with someone known to be HIV positive. On the other end of the spectrum is the risk calculated for insertive oral sex: 1 in 20,000 if condoms are not used and the receptive partner is known to be HIV positive.
Making personal decisions about unprotected sexual activity using these numbers is not recommended. For starters, these numbers are based on assumptions and guesses, not actual evidence of HIV transmission. Second, even if the researchers are right – that there is a 1 in 20,000 chance of being infected with HIV via unprotected insertive oral sex with someone known to be positive – many experts argue that this number is close enough to zero as to not be concerned about it at all.
Just as these numbers can unnecessarily scare people, they can also give some people a false sense of security. For example, the 1 in 200 risk associated with receptive anal sex with someone known to be HIV positive doesn't mean that you can have unprotected anal sex 199 times before becoming infected. It's very possible to become infected with HIV after just one incident of unprotected receptive anal intercourse.
It's also important to stress that there are a number of factors than can influence the risk of HIV transmission. Because there are so many factors, it's virtually impossible to interpret per-act or per-contact risk numbers when making personal decisions about sexual activity (or looking back on previous decisions). For example, HIV-positive people with very high viral loads (high amounts of HIV in their blood and genital secretions) may be more likely to transmit the virus to their partners, during unprotected insertive anal, vaginal, or oral sex. The presence of STDs, especially ulcerative STDs, can increase the risk of spreading (or becoming infected with) HIV. Trauma – such as abrasions or cuts inside the vagina, anus, mouth, or on the penis – can also increase the risk of transmission. All of these can increase the per-act risk of HIV transmission.
How can the sexual transmission be prevented?
Male Condoms
Several studies have demonstrated that male condoms made of either latex or polyurethane are effective barriers against HIV. The theory behind using condoms is clear: they cover the penis and provide an effective barrier to exposure to secretions such as semen and vaginal fluids, thereby blocking sexual transmission of HIV infection.
Laboratory studies have been conducted to support this theory. These studies involved placing a solution containing HIV inside the condoms. No leakage of HIV across the latex or polyurethane condoms was demonstrated. Similar studies have also demonstrated that other common sexually transmitted viral infections, such as herpes simplex virus (HSV) and hepatitis B virus (HBV), are also prevented with the use of these two types of condoms.
Condoms made of "natural" materials – such as lambskin – are not a consistently effective barrier against many viruses. In one laboratory study, HIV was found to pass through microscopic holes in lambskin condoms. Studies involving HSV and HBV reported similar results. In turn, lambskin condoms are not a recommended barrier against HIV and other viral infections.
There have been a number of epidemiologic studies – studies that are conducted in real-life setting, where one partner is infected with HIV and the other partner is not – that have demonstrated consistent use of latex (or polyurethane) condoms provide a high degree or protection against HIV. However, the key to effective protection is consistent and correct use of condoms.
Incorrect use of condoms can increase the risk of condom slippage or breakage, which diminishes their protective effect. Inconsistent use – for example, failure to use condoms with every act of vaginal or anal intercourse – can lead to HIV transmission. As is discussed in "What about the per-risk numbers," HIV transmission can occur with a single act of intercourse with someone who is HIV positive or has an unknown HIV status.
A word about polyurethane condoms: They are an effective alternative to latex condoms, especially for people with an allergy to latex. There have been at least six epidemiologic studies of polyurethane condoms. Three of the studies found that that slippage and breakage occurs equally (and rarely) with both latex and polyurethane condoms. The three other studies found that polyurethane condoms are more likely to break than latex condoms (with one of the studies also demonstrating that polyurethane condoms are more likely to slip than latex condoms). Still, if used consistently and correctly, they are considered to be a highly effective barrier against the sexual transmission of HIV.
Female Condoms
The female condom, approved in 1993 for use in the United States, is a polyurethane pouch with flexible polyurethane rings and each end. It is inserted deep in the vagina, much like a diaphragm. The ring at the closed end holds the pouch in the vagina. The ring at the open end stays outside the vulva (vaginal opening). If inserted properly, it lines the vagina and the cervix, which helps to prevent pregnancy, along with HIV and other sexually transmitted infections.
While female condoms are not approved for use during anal intercourse, some MSM have reporting using them for anal sex. However, at least one study has reported problems for the receptive partner using the female condom, including difficulty inserting the condom, discomfort, and rectal bleeding (removing the inner ring may alleviate some of the problems experienced during anal insertion and removal).
How are condoms used correctly?
Contrary to popular opinion, it's not only the sexually inexperienced who aren't familiar with how to use a condom effectively. Whether you're just starting to have sex – or have been going at it for years – a little information may be useful and important.
- Men: Practice using male condoms while masturbating. MSM hoping to use female condoms for receptive anal sex are also encouraged to practice inserting and removing the condom before using it during intercourse.
- Women: Practice using male condoms on penis-shaped objects, including ketchup bottles or bananas. Practicing the insertion and removal of female condoms, before they are used during vaginal intercourse, is also recommended.
Remember that the condom must be on the penis before it is inserted into the vagina or anus. The same holds true for female condoms – they must be inserted properly before intercourse begins.
Male condoms should be used only once. Use a new male condom for each episode of intercourse. One study has suggested that female condoms can be reused up to five times, provided that they are disinfected with bleach and water. However, experts caution that the safest way to use female condoms is to use them only once and then discard them.
Here are the key points that always need to be remembered when using male condoms:
Putting on a condom:
|
Condoms are individually sealed in aluminum or plastic wrapping. Be careful not to tear the condom while unsealing it. Never use a condom that is torn or seems brittle or stiff, past its expiration date, or exposed to extreme heat or cold. |
|
If not circumcised, pull back the foreskin before rolling on the condom. |
|
Leave a half-inch space at the tip of the condom to collect semen. Pinch the air out of the tip with one hand while unrolling the condom over the penis with the other hand. |
|
Roll the condom down to the base of the penis. |
|
Smooth out any air bubbles and lubricate the outside of the condom generously. |
|
Use only one condom at a time. Using two condoms at a time, including two male condoms or a male and a female condom, can increase friction and lead to breakage. |
Taking the condom off:
|
Be sure to pull out of the vagina or anus before the penis goes soft. |
|
Clasp the condom against the base of the penis while pulling out. |
|
Throw the condom away immediately. |
|
Wash the penis with soap and water before post-sex intimacy. |
If the condom breaks during intercourse:
|
Pull out quickly and replace it. Men should be able to tell if a condom breaks during intercourse. To learn what it feels like, men should purposely break a condom while masturbating. |
|
If semen leaks out during intercourse and the insertive partner is HIV positive (or his HIV status is not known), contact a healthcare provider or hospital emergency room to discuss the risk and the possibility of post-exposure prophylaxis (PEP).
PEP involves a 28-day course of anti-HIV drugs that needs to be started within 72 hours of possible exposure to the virus. Generally speaking, only people who have had a high-risk situation (e.g., condomless receptive anal or vaginal intercourse with someone known to be HIV positive) are considered to be good candidates for PEP. |
A word about lubricants
Only water-based and silicone-based lubricants should be used with latex condoms. K-Y Jelly®, Wet®, and Astroglide® are three examples of water-based lubricants that can be used with latex condoms. Examples of silicone-based lubricants include Millennium ID® and Eros Bodyglide®
Never use oil-based lubricants, including hand or body lotion, baby oil, vegetable oil or shortening, massage oil, mineral oil, or petroleum jelly (e.g., Vaseline®). Oil-based lubricants can damage latex and cause latex condoms to tear more easily.
Some pre-lubricated condoms and separately sold lubricants contain a chemical called nonoxynol-9. While nonoxynol-9 has been shown to kill sperm (and potentially reduce the risk of pregnancy) and various sexually transmitted infections, some men and women are allergic to this chemical. This can cause irritation inside the vagina and anus, which can increase the risk of HIV transmission if the condom breaks.
When In Doubt, Test!
While we know that some types of sexual activities are much lower risk than others (with some activities only being a theoretically risk, not a proven risk) and the proven effectiveness of condoms, there are no guarantees. The fact is, it is very difficult to be 100% certain that you did not engage in any risk behavior, especially if you have any sort of unprotected sexual activity with a person known to be HIV positive or you do not know what his or her HIV status is. Abstinence – or sexually activity only in a monogamous relationship in which both partners are HIV negative – is the only way to eliminate the risk of HIV infection.
The only way to know for sure whether you have been infected, even after an activity that is considered to be very low risk for HIV transmission, is to get tested. For more information about testing, please read AIDSmeds.com's comprehensive lesson on this subject:
Am I Infected? (A Complete Guide to Testing for HIV)
Search for news stories about this topic