This article first appeared on the website of Pacific AIDS Network here.  Republished with permisision of the author. Folllow PAN on twitter at @PAN_CBR

I didn’t attend AIDS 2012 in Washington last July, but I do remember that when others came back they were all abuzz about the concept of the treatment cascade as possibly the next “big thing” in the way that we conceptualize HIV prevention and treatment. Now, many months later, and numerous references to the treatment cascade in meetings, policy documents, articles, and other HIV-discourse hubs later, I have to give my AIDS 2012-attending friends and colleagues pats on the back because I think they were right.

This example of an HIV cascade of prevention and care appears in the 2012 document “From Hope To Health,” which lays out the BC government’s framework for the provincial expansion of the STOP HIV/AIDS program.

While the meme of “AIDS free generation” also took hold at AIDS2012, it’s purpose was mainly to offer hope and buoy a movement, while the treatment cascade seems to be a model that is transforming how we approach HIV treatment and work to identify gaps in the continuum of care (from prevention, to testing, to care and treatment) so that fewer individuals are lost along the way.

Roughly defined, the HIV treatment cascade (or the cascade in care) is a way of calculating what proportion of HIV in a country or community is on anti-retroviral treatment and is virally suppressed – meaning no detectable virus in the blood – and how many people “fall off” the cascade at each step. Below are some interesting and key documents to look at in order to build an understanding of this concept.

From Hope to Health: Towards an AIDS-free Generation – On December 1, 2012, the British Columbia Ministry of Health released a guidance document for the province’s expansion of the Seek and Treat for Optimal Prevention (STOP) project across the province. What was notable in the document was the inclusion of a figure illustrating a “treatment and care cascade for BC” (see image above), which was expanded from the traditional cascade model to also include “number of people at risk for HIV but not infected” as the starting point. It will be very interesting to see how the model is implemented. 

The HIV treatment cascade – patching the leaks to improve HIV prevention – This comprehensive article written by James Wilton and Logan Broeckaert at CATIE is excellent in that translates the treatment cascade by explaining each “step” of the cascade and provides real-world examples of interventions and services that are used to help stop the leaks in the cascade. Wilton and Broechaert also address a concern regarding human rights that arises when using models such as this, which may reduce people to numbers and risk the goal (ie of low viral load in a population) seeming more important than individual agency. They say, “It’s critical that human rights are respected and that people living with or at risk of HIV are empowered to make decisions about testing and treatment that are right for them.”

Grappling with the HIV Treatment Cascade – In this PositiveLite.com article (originally published aidsmap.com), Gus Cairns looks at reports from the USA and Europe in terms of the proportion of individuals that are virally suppressed. This piece is interesting because it indicates that – although that the treatment cascade is a model that allows us to conceptualize the proportion of a population that has been tested and is retained in care – it is not a simple task to obtain actual numbers for each step. As PositiveLite.com editors suggest, without reliable data on the actual numbers, more research is certainly needed to confirm the extent of treatment penetration and to monitor future treatment as prevention initiatives.

North American Housing and HIV/AIDS Research Summit VII: Closing the Housing Gap in the HIV Treatment Cascade – This upcoming conference, to be held in Montreal in late September 2013, is a great example of the where the concept of treatment cascade is going next. As the title of the conference suggests, there is certainly a need to query how the social determinants of health, such as housing, inequitable distribution of resources, gender, food security, etc., can impact how many people are “lost” at each step of the cascade. The Summit will explore the potential of housing strategies to improve HIV treatment effectiveness in various jurisdictions. I believe that this is the tip of the iceberg in how we will be seeing various segments of the HIV service and research community engage with this concept.

Questions? Feedback? Get in touch!

Andrea Langlois (above) is the Community-Based Research Manager, Pacific AIDS Network. She is on twitter at @PAN_CBR.

This article by James Wilton originally appeared on the CATIE http://www.catie.ca/en/home  website here. 

Une version française est disponible ici.

The sexual transmission of HIV occurs after an exposure to fluids that contain HIV, such as semen and fluids from the vagina and rectum. Research shows that a higher amount of HIV (viral load) in these fluids increases the risk of HIV transmission and that a lower viral load decreases the risk.1

Treatment, viral load and HIV transmission

The viral load in the blood of a person living with HIV is measured to monitor the success of antiretroviral therapy (also called ART, HAART or cART). Successful HIV treatment can reduce the viral load in the blood (and other bodily fluids) to undetectable levels and thereby reduce the risk of sexual HIV transmission. In fact, a research study known as HPTN 052 found that the risk of HIV transmission among heterosexual serodiscordant couples was 96% lower when the HIV-positive partner was on treatment.2 (In serodiscordant couples, one partner is HIV-positive and the other is HIV-negative.)

Undetectable viral load does not mean that there is no virus, but rather that the amount of HIV in a bodily fluid is below a level that tests can detect. (Tests used in some places, such as Canada, cannot detect HIV if there are less than 40 copies of HIV per ml of blood, while tests used in other parts of the world have higher limits of detection.)

Also, not all people living with HIV who take HIV treatment and have an undetectable viral load in the blood also have an undetectable viral load in their other bodily fluids. Research suggests that of those people living with HIV who have an undetectable blood viral load, 5 to 48% can have detectable virus in their semen, vaginal fluid and rectal fluid.3,4,5

Although previous research has demonstrated that treatment can reduce the risk of HIV transmission in heterosexual couples, it is unclear exactly what the HIV transmission risk is when a person’s blood viral load is undetectable. A recent systematic review6 of the literature was conducted by Dr. Mona Loutfy, one of Canada’s leading infectious disease specialists, and colleagues to gain a better understanding of this risk.

Systematic review

The authors searched for published studies that followed serodiscordant heterosexual or same-sex couples over time. The main purpose of the review was to find studies that met the following criteria:

• the HIV-positive partner was on antiretroviral treatment
• the number of HIV infections in the HIV-negative partner was recorded
• if HIV transmission occurred, the HIV-positive partner’s blood viral load was measured close to the time of transmission

The authors identified only three studies that fit all of their criteria. These studies followed a total of 222 heterosexual couples from Brazil, Spain and Uganda.

An additional three studies were identified that fit all of their criteria but did not measure the viral load of the HIV-positive partner near the time of HIV transmission, including the HPTN 052 randomized controlled trial. These studies enrolled a total of 1,304 couples on treatment.

Overall, these six studies contained 2,975 person-years follow up of treated couples. This is the equivalent of following 2,975 couples for one year. The vast majority of these couples were heterosexual and only a small number were same-sex couples (3% of the couples in the HPTN 052 study were same-sex).

Number of HIV transmissions and HIV transmission risk

In the three studies where viral load was measured, no HIV transmissions occurred among couples where the HIV-positive partner was on treatment and the viral load was undetectable.

In the additional three studies, for which viral load was not measured, a total of four transmissions occurred. However, it is not known if the viral load of the HIV-positive partner was detectable or undetectable at the time of transmission. All of these HIV transmissions occurred shortly after the HIV-positive partner started treatment; therefore, the viral load was likely declining but still detectable when transmission occurred.

In these six studies, the definition of undetectable viral load ranged from less than 50 copies per ml to less than 500.

The lack of HIV transmissions in these studies does not mean there is no risk of HIV transmission when the viral load is undetectable. Using data from all six studies (but excluding the four HIV transmissions that occurred in the additional three studies), the authors calculated that when the viral load is undetectable, there may be a 1% risk of HIV transmission per 10 years of relationship and sexual activity.

Limitations of the study findings

There are several factors—other than viral load—that can influence the risk of HIV transmission between serodiscordant couples and may partly explain the lack of HIV transmissions observed in this review. As a result, the authors of the systematic review listed several caveats to their findings, including the lack of data on:

1.Extent of condom use 

Condoms are an effective method of preventing the transmission of HIV and many STIs and couples in these studies may have been using condoms often. For example, in the HPTN 052 study, 96% of the couples reported using condoms every time they had sex. Although people often say they use condoms more than they actually do, condom use may have played an important role in keeping the number of HIV transmissions low in these studies.

2. Same-sex couples and type of sexual intercourse

The vast majority of the couples enrolled in the studies were heterosexual and were (likely) having mostly vaginal sex. Therefore, it is unclear how much these findings apply to same-sex couples and other couples who mostly have anal sex. Some researchers think the risk of HIV transmission when undetectable may be higher for anal sex compared to vaginal sex.

3. Rates of sexually transmitted infections (STIs)

STIs are known to increase the risk of HIV-positive people transmitting HIV and HIV-negative partners becoming infected. STIs may increase the risk of HIV transmission even when a person’s viral load is undetectable. However, most of the studies reviewed did not provide data on STIs other than HIV; therefore, the review could not evaluate their impact.

In general, the risk of having STIs is lower among stable heterosexual couples (particularly those who are monogamous) than among people in casual relationships. Also, in some studies, such as the HPTN 052 study, participants were provided with regular STI testing and treatment which can help to further reduce the rate of STIs. A low number of STIs among couples in these studies may have decreased the risk of HIV transmission.

Conclusion

This systematic review supports previous research showing that treatment can significantly reduce the risk of HIV transmission among heterosexual couples. The authors concluded: “Our findings suggest minimal risk of sexual HIV transmission for heterosexual serodiscordant couples when the HIV-positive partner has full viral suppression on cART with caveats regarding information on sexual intercourse type, STIs, and condom use. These findings have implications when counseling heterosexual serodiscordant couples on sexual and reproductive health.”

Research is ongoing to gain a better understanding of the risk of HIV transmission (a) when the HIV-positive partner’s viral load is undetectable and condoms are not used and (b) in same-sex serodiscordant couples where the HIV-positive partner is taking ART.

RESOURCE:

Understanding Risk: A Conversation

REFERENCES:

 1. Baeten JM, Kahle E, Lingappa JR et al. Genital HIV-1 RNA predicts risk of heterosexual HIV-1 transmission. Science Translational Medicine. 2011 Apr 6;3(77):77ra29.

 2. Cohen MS, Chen YQ, McCauley M et al. Prevention of HIV-1 infection with early antiretroviral therapy. New England Journal of Medicine. 2011 Aug 11;365(6):493–505.

 3. Marcelin A-G, Tubiana R, Lambert-Niclot S et al. Detection of HIV-1 RNA in seminal plasma samples from treated patients with undetectable HIV-1 RNA in blood plasma. AIDS. 2008 Aug 20;22(13):1677–9.

 4. Sheth PM, Yi TJ, Kovacs C et al. Mucosal correlates of isolated HIV semen shedding during effective antiretroviral therapy. Mucosal Immunology. 2012 May;5(3):248–57.

 5. Sheth PM, Kovacs C, Kemal KS et al. Persistent HIV RNA shedding in semen despite effective antiretroviral therapy. AIDS. 2009 Sep 24;23(15):2050–4.

 6. Loutfy MR, Wu W, Letchumanan M et al. Systematic Review of HIV Transmission between Heterosexual Serodiscordant Couples where the HIV-Positive Partner Is Fully Suppressed on Antiretroviral Therapy. PLoS ONE. 2013 Feb 13;8(2):e55747.

This important article by James Wilton first appeared in Prevention in Focus on the CATE website here.

Une version française est disponible ici. 

Since the beginning of the HIV epidemic, condoms have been a cornerstone of our HIV prevention efforts—often promoted as the most effective way to prevent the sexual transmission of the virus. However, in the past few years the number of HIV prevention options has increased and some people are interested in, or are already using, newer strategies. As a result, frontline service providers are being asked challenging questions: Are condoms the most effective strategy available? How do they compare to other strategies? This article explores the evidence on how effectively condoms prevent HIV transmission and the implications for our HIV prevention messaging.

Condoms 101

Condoms are physical barriers used during sex to prevent parts of the body that are vulnerable to HIV infection (such as the penis, vagina, rectum and mouth) from coming into contact with fluids that may contain HIV and other infections. We currently have two main types of condoms: the male condom (also known as the external condom) and the female condom (also known as the internal or insertive condom).

What are they made of? Most male and female condoms are made from nitrile, latex, polyisopropene or polyurethane, all of which cannot be penetrated by the viruses and bacteria that cause sexually transmitted infections (STIs), including HIV.1 Lambskin condoms, which are made from sheep intestines, can be penetrated by bacteria and viruses and should therefore never be used to prevent the transmission of HIV.

To lube or not to lube? Sexual lubricants are commonly used in combination with condoms to increase pleasure. The use of lubricant is also recommended to decrease friction that can cause breakage, particularly during anal sex. Water- and silicone-based lubricants are safe to use with all condoms, but oil-based lubricants can compromise the integrity of latex and polyisopropene condoms and increase the risk of the condom breaking.

Using condoms correctly and consistently

Since condoms are impermeable to viruses, shouldn’t we expect them to be 100% protective against HIV? Unfortunately, it’s not that simple. As with any type of prevention strategy, condoms only work if they are used correctly and consistently. Inconsistent use can greatly decrease their ability to prevent HIV transmission.

Incorrect use of condoms can also compromise their effectiveness. For example, some people may use condoms that are too small or too large, damaged or expired; unroll condoms before putting them on; not pinch the tip when putting them on; use sharp objects to open condom packages; not use enough lubrication in combination with condoms or use oil-based lubrication with latex or polyisopropene condoms; or not hold the rim of the condom when pulling out. All of these can potentially increase the risk of HIV transmission by causing a condom to break, slip or leak.

Incorrect condom use can also take the form of putting on a condom late (after intercourse has started), removing the condom early (before ejaculation has occurred) or putting the condom on inside out and then flipping it over to use. If a condom is used incorrectly in these ways, then HIV transmission could occur even though the condom does not break, slip or leak.

A recent literature review of 50 studies revealed that the incorrect use of male condoms is surprisingly common.2 For example:

• Studies found that 17 to 51% of participants reported not putting on a condom until after intercourse had started.
• Some studies also reported high rates of condom problems, such as breakage (0 to 33%), slippage (0 to 78%) and leakage (0 to 7%), which could lead to HIV transmission. Errors in condom use may be partly responsible for these problems. For example, 24 to 46% of participants reported not pinching the tip of the condom and 16 to 26% reported using a condom that was not lubricated.

How often do condoms break, slip or leak when they are used perfectly in every possible way? We don’t know and probably never will. However, when condoms are used correctly, the rates of breakage, slippage, and leakage are likely quite low. Research shows that education and more experience using condoms can help lower rates of condom failure.3,4

So how effective are male condoms?

The best evidence we have on the effectiveness of male condoms comes from an analysis of 14 observational studies that enrolled heterosexual serodiscordant couples (where one partner is HIV-positive and the other is HIV-negative).5 The analysis compared the rate of HIV transmission between couples who said they always used male condoms to the rate among couples who said they never used male condoms. The analysis found that the rate of HIV transmission was 80% lower among couples who reported always using condoms.

For many people working in HIV prevention, an 80% effectiveness rate may be lower than you thought or have previously told clients and patients. However, it is important to consider the limitations of this analysis when interpreting its results. There are three reasons why this analysis may make condoms look less effective than they can be: 

Incorrect use. The couples who said they always used condoms may not have been using condoms correctly. This would have increased their risk of HIV transmission and reduced condom effectiveness.

Inconsistent use. The couples who said they always used condoms, in reality, may not always use them! Some of the couples may have had trouble remembering how often they used condoms or felt uncomfortable saying that they did not use condoms. This would have increased their risk of HIV transmission and made condoms appear less effective.

Differences in behaviour. The risk-taking behaviours of the couples who said that they always used condoms may have been different from those couples who said they never use condoms. For example, couples who reported always using condoms may have engaged in behaviours that increased their risk of HIV transmission, such as having sex more often or engaging in higher-risk types of sex. If this was the case, these behaviours would have increased their risk of HIV transmission, making condoms appear to be less effective. It’s also possible that people who reported never using condoms may have engaged in behaviours that put them at lower risk of HIV transmission, such as having sex less often or only engaging in lower-risk types of sex (such as oral sex). If this was the case, this would make it appear as though there was less of a difference in HIV transmission rate between the two groups and make condoms appear less effective.

Given these limitations, the estimate of 80% likely does not reflect how effective condoms can be in preventing heterosexual HIV transmission. If used consistently and correctly, condom effectiveness is likely much higher.

Is the same true for men who have sex with men?

Are male condoms also effective at reducing HIV transmission when used by gay men or other men who have sex with men? Several studies have explored this question and estimated a similar effectiveness rate of 70 to 80% for consistent condom use during anal sex.6,7,8 However, these studies are affected by the same three limitations as studies of heterosexual couples—incorrect use, inconsistent use and differences in behaviour. So the effectiveness rate for consistent and correct condom use during anal sex is likely higher.

What about female condoms?

No studies have evaluated the effectiveness of female condoms in preventing HIV transmission during vaginal sex or anal sex. However, research shows that they are as effective as male condoms at preventing other STIs.9,10,11

The expanding HIV prevention toolkit

In the past decade the number of HIV prevention options available to reduce the risk of HIV transmission has increased. Some of these strategies are generating a lot of excitement because they may provide an option for people who don’t want to, or are unable to, use condoms. These include the following:

Antiretroviral treatment – which reduced the risk of HIV transmission by 96% among heterosexual serodiscordant couples in a randomized controlled trial (RCT).12

Pre-exposure prophylaxis (PrEP) – which reduced the risk of HIV transmission by 40 to 70% for gay men13 and heterosexual men and women14,15 in RCTs. Further analysis suggested that PrEP may have reduced HIV risk by up to 90% among those who always took their pills.13,14

Post-exposure prophylaxis (PEP) – which reduced the risk of HIV transmission by up to 80% in an observational study of healthcare workers exposed to HIV in the workplace.16

Observational studies suggest that behavioural strategies such as serosorting, strategic positioning and withdrawal may slightly reduce the risk of HIV transmission.17

People who want to use, or are already using, these strategies may want to know how effective they are compared to condoms. These questions can be challenging to answer and it’s important that, in our responses, we don’t compare apples and oranges. For example, comparing results from different types of studies can be problematic. Some of the new prevention strategies were evaluated using an RCT while condoms were evaluated using observational studies. Comparing the results from these two kinds of studies can be problematic for a number of reasons:

• In RCTs the two groups are randomized to ensure that there are no differences between the groups other than whether or not they received the intervention. This is important because we know that each group should have similar risk behaviours and that neither group should be more or less likely to get HIV. However, in observational studies (such as those used to assess condoms), one group could be having sex more often or engaging in riskier sex. This could impact the results and make a strategy, such as condoms, appear to be less effective than they actually are.
• RCTs create “ideal” conditions that can make a strategy appear more effective than it would be in the “real world.” For example, RCT participants are supported to ensure they use the strategy correctly and all participants are provided with a comprehensive package of prevention services, including STI testing and treatment, free condoms, and intensive adherence and risk-reduction counselling. By contrast, observational studies, such as those used to evaluate condoms, generally do not provide participants with additional supports. Therefore, these results may not be directly comparable to the results of RCTs.

When it comes to comparing the effectiveness of two prevention strategies, we need to pay attention to the research design used to measure that effectiveness. Most new prevention strategies, such as PrEP or treatment as prevention, have been evaluated using RCTs, which can tell us about the effectiveness of the strategy under “ideal conditions.” Unfortunately, we don’t know how effective condoms would be under the ideal conditions of an RCT; however, we have good reason to believe that they would be more than 80% effective when used consistently and correctly.

Implications for HIV prevention messaging

Safer sex messaging and prevention counselling need to emphasize that the correct and consistent use of condoms is a very highly effective method of preventing the sexual transmission of HIV.

When answering questions about the effectiveness of condoms, it’s important to emphasize that they have several advantages over other options. Key messages include the following:

• If a condom is used correctly and it doesn’t break, slip or leak, then it is virtually 100% protective. However, there is a still a possibility that condoms will break, slip, or leak even when used correctly. Condoms do not eliminate the risk of HIV transmission.
• Condom effectiveness does not rely on accurate knowledge of a person’s HIV status, as opposed to serosorting, which requires accurate knowledge of the HIV status of both partners—something that is often difficult to know for certain.
• Whereas the goal of some other strategies—such as PEP, PrEP or having an undetectable viral load— is to reduce the risk of an exposure leading to an infection, condoms prevent an exposure to HIV from occurring in the first place.
• Other prevention options may be less effective if either partner has an STI, a higher viral load or other biological factors that affect HIV risk whereas condom effectiveness is not affected by these.
• If they don’t break, slip or leak, condoms can reduce the risk of HIV transmission for both anal and vaginal sex to the same level. However, the risk of HIV transmission while using PrEP or when the viral load is undetectable may be higher for anal sex than for vaginal sex. (This is because anal sex has a higher baseline risk of HIV transmission than vaginal sex.18)
• Condoms also reduce the risk of other STIs, such as gonorrhea, chlamydia, herpes and syphilis.19 Although other strategies may reduce the risk of HIV transmission, they do not reduce the risk of STI transmission. This is important because STIs can increase a person’s risk of HIV transmission.20
• Condoms can reduce the risk of unintended pregnancy.
• Condoms are less expensive, more readily available and less toxic than strategies that involve antiretroviral medications, such as PEP and PrEP.

Despite the advantages of condoms, we can’t ignore the important role that other prevention strategies may play in helping someone reduce their risk of HIV transmission. Condoms are not without their disadvantages and these can make it difficult for people to use them consistently and correctly. For example, condom use can be difficult to negotiate, condoms can decrease sexual pleasure and intimacy, they need to be available at the time of intercourse, they may be difficult to use when under the influence of alcohol or drugs, and they do not allow a woman to conceive. For these reasons, some people may choose to reduce their risk of HIV transmission in other ways.

Conclusion

HIV prevention efforts need to focus on helping people adopt prevention strategies that are appropriate to their circumstances and will be most effective for them. If people are having difficulty using condoms or are having problems with condom breakage, slippage or leakage, counselling may help them use condoms more consistently and correctly.

At the same time, alternative strategies for reducing the risk of HIV transmission may need to be discussed with these clients. When exploring other prevention options, it’s important to clearly explain their limitations, factors that may decrease their effectiveness and how a person can keep their risk of HIV transmission as low as possible while using these strategies. No strategy—including condoms—is 100% effective; all have their limitations and can fail in different ways. Since condoms provide less than 100% protection, using other strategies in combination with condoms will help decrease a person's overall risk of HIV transmission. However, if a client or patient decreases their condom use in favour of a less protective strategy, they may be increasing their overall risk of HIV transmission.

Resources

AIDSMAP – Do condoms work?

CATIE News – High prevalence of condom use errors and problems – implications for HIV prevention messaging

Canadian HIV/AIDS Legal Network – HIV non-disclosure and the criminal law: Implications of recent Supreme Court of Canada decisions for people living with HIV: Questions & Answers

References

1. Lytle CD, Routson LB, Seaborn GB, Dixon LG, Bushar HF, Cyr WH. An in vitro evaluation of condoms as barriers to a small virus. Sex Transm Dis. 1997 Mar;24(3):161–4.

2. Sanders SA, Yarber WL, Kaufman EL, Crosby RA, Graham CA, Milhausen RR. Condom use errors and problems: a global view. Sex. Health. 2012 Feb 17;9(1):81–95.

3. Lindberg L, Sonenstein F, Ku L, Levine G. Young men’s experience with condom breakage. Family Planning Perspectives. 1997 Jun;29(3):128–31.

4. Steiner MJ, Taylor D, Hylton-Kong T, Mehta N, Figueroa JP, Bourne D, et al. Decreased condom breakage and slippage rates after counseling men at a sexually transmitted infection clinic in Jamaica. Contraception. 2007 Apr;75(4):289–93.

5. Weller S, Davis K. Condom effectiveness in reducing heterosexual HIV transmission. Cochrane Database Syst Rev. 2002;(1):CD003255.

6. Vittinghoff E, Douglas J, Judson F, McKirnan D, MacQueen K, Buchbinder SP. Per-contact risk of human immunodeficiency virus transmission between male sexual partners. Am. J. Epidemiol. 1999 Aug 1;150(3):306–11.

7. Golden M. HIV serosorting among men who have sex with men: implications for prevention. 13th Conference on Retroviruses and Opportunistic Infections. 2006;Abstract 163.

8. Detels R, English P, Visscher BR, Jacobson L, Kingsley LA, Chmiel JS, et al. Seroconversion, sexual activity, and condom use among 2915 HIV seronegative men followed for up to 2 years. J. Acquir. Immune Defic. Syndr. 1989;2(1):77–83.

9. Minnis AM, Padian NS. Effectiveness of female controlled barrier methods in preventing sexually transmitted infections and HIV: current evidence and future research directions. Sex Transm Infect. 2005 Jun;81(3):193–200.

10. French PP, Latka M, Gollub EL, Rogers C, Hoover DR, Stein ZA. Use-effectiveness of the female versus male condom in preventing sexually transmitted disease in women. Sex Transm Dis. 2003 May;30(5):433–9.

11. Kelvin EA, Mantell JE, Candelario N, Hoffman S, Exner TM, Stackhouse W, et al. Off-label use of the female condom for anal intercourse among men in New York City. Am J Public Health. 2011 Dec;101(12):2241–4.

12. Cohen MS, Chen YQ, McCauley M, Gamble T, Hosseinipour MC, Kumarasamy N, et al. Prevention of HIV-1 infection with early antiretroviral therapy. N. Engl. J. Med. 2011 Aug 11;365(6):493–505.

13.a. b. Grant RM, Lama JR, Anderson PL, McMahan V, Liu AY, Vargas L, et al. Preexposure chemoprophylaxis for HIV prevention in men who have sex with men. N. Engl. J. Med. 2010 Dec 30;363(27):2587–99.

14.a. b. Baeten JM, Donnell D, Ndase P, Mugo NR, Campbell JD, Wangisi J, et al. Antiretroviral prophylaxis for HIV prevention in heterosexual men and women. N. Engl. J. Med. 2012 Aug 2;367(5):399–410.

15. Thigpen MC, Kebaabetswe PM, Paxton LA, Smith DK, Rose CE, Segolodi TM, et al. Antiretroviral preexposure prophylaxis for heterosexual HIV transmission in Botswana. N. Engl. J. Med. 2012 Aug 2;367(5):423–34.

16. Cardo DM, Culver DH, Ciesielski CA, Srivastava PU, Marcus R, Abiteboul D, et al. A case-control study of HIV seroconversion in health care workers after percutaneous exposure. Centers for Disease Control and Prevention Needlestick Surveillance Group. N. Engl. J. Med. 1997 Nov 20;337(21):1485–90.

17. Vallabhaneni S, Li X, Vittinghoff E, Donnell D, Pilcher CD, Buchbinder SP. Seroadaptive Practices: Association with HIV Acquisition among HIV-Negative Men Who Have Sex with Men. PLoS ONE. 2012;7(10):e45718.

18. Boily M-C, Baggaley RF, Wang L, Masse B, White RG, Hayes RJ, et al. Heterosexual risk of HIV-1 infection per sexual act: systematic review and meta-analysis of observational studies. Lancet Infect Dis. 2009 Feb;9(2):118–29.

19. Holmes KK, Levine R, Weaver M. Effectiveness of condoms in preventing sexually transmitted infections. Bull. World Health Organ. 2004 Jun;82(6):454–61.

20. Ward H, Rönn M. Contribution of sexually transmitted infections to the sexual transmission of HIV. Curr Opin HIV AIDS. 2010 Jul;5(4):305–10.

About the author: 

James Wilton is the Coordinator of the Biomedical Science of HIV Prevention Project at CATIE. James is currently completing his master’s degree of Public Health in Epidemiology at the University of Toronto and has completed an undergraduate degree in Microbiology and Immunology at the University of British Columbia.

This article first appeared on the website of Pacific AIDS Network here. Republished with permisision of the author. Folllow PAN on twitter at @PAN_CBR 

Moving research on new “biomedical” HIV prevention technologies into practice

By James Wilton

Recent research findings have improved our understanding of HIV transmission and prevention and could change the landscape of our response to the HIV epidemic. In the past few years, several new HIV prevention approaches, such as post-exposure prophylaxis (PEP), pre-exposure prophylaxis (PrEP), and the use of antiretroviral treatment as prevention, have been found to reduce the risk of HIV transmission. These new strategies are often referred to as new “biomedical” HIV prevention technologies, or NPTs.

If moved into practice in an appropriate way, these new approaches could have a dramatic impact on the HIV epidemic in Canada and other parts of the world. However, translating this research into a reduction in new HIV infections within the communities we work with will be challenging. Community-based organizations (CBOs) – through programming and research – will have an important role to play in understanding these challenges, overcoming them, and effectively implementing these approaches.

Engaging people and communities in new HIV prevention approaches

At the most basic level, we know that the more people in a population who use a specific strategy, the more HIV transmissions they can potentially prevent. The number of people who use a strategy, often referred to as uptake or adoption, will depend on a number of factors, such as awareness (do people know about it?), acceptability (do people want to use it?) and availability (can people access and afford the technology if they want to use it?).

The impact of these strategies will also depend on “who” in a population uses them. More HIV transmissions will be prevented if the strategies are adopted by individuals who are at highest risk of HIV transmission, such as those who don’t use condoms consistently or share injection drug use equipment.

Focusing uptake among those at highest risk may be important for another reason. There is a concern that some people using these new approaches may feel a false sense of security and increase their risk behaviour, such as using fewer condoms or having sex with more partners (a concept known as risk compensation or behavioural disinhibition). Since none of these new strategies are 100% protective, this could potentially offset some of the benefit of NPTs and limit the number of HIV infections they prevent. However, the potential impact of risk compensation will be lower when used by people who are already at higher risk of HIV transmission.

Community-based organizations will play a key role in engaging individuals and communities and facilitating the appropriate uptake of these technologies. This will involve:

• Community mobilization to build readiness for new approaches and address barriers that may affect their acceptability, such as stigma and social, cultural, and political norms.
• Outreach and educational campaigns to improve awareness of these strategies, including information on who they are appropriate for and where they can be accessed, particularly among those at highest risk for HIV transmission.
• Accurate risk assessments for those who are interested in using these approaches and, if appropriate, referral to locations where they can be accessed.
• Community planning to ensure NPTs are provided in a way that respects human rights and supports informed decision making by the people using them.
• Advocacy to ensure the technologies are available and affordable.

Community-based research (CBR) will be essential to gain a better understanding of the acceptability, awareness and availability of these technologies in the community, the barriers to adopting them, and the characteristics of those who are using them.

Packaging new approaches with other strategies and supports

Among those who do use these strategies, what will influence the effectiveness of NPTs at reducing HIV incidence?

How consistently and correctly these strategies are used will be important. Research shows that these new approaches – such as post-exposure prophylaxis (PEP), pre-exposure prophylaxis (PrEP), and the use of antiretroviral treatment as prevention – are much less protective if not used consistently. Correct use means different things for different strategies. However, as none of these new approaches are 100% protective, correct use generally means that these new approaches are combined with, instead of replace, existing HIV prevention strategies.

Furthermore, the presence of certain biological factors that are known to increase HIV risk, such as sexually transmitted infections (STIs), may reduce the effectiveness of these new approaches. Therefore, correct use of these strategies also means combining them with STI prevention, testing, and treatment services.

In research studies and clinical trials, these NPTs have been credited with dramatic reductions in HIV incidence and this has generated a lot of excitement. For example, the HPTN 052 study found that antiretroviral treatment reduced HIV incidence among heterosexual serodiscordant couples by 96%.

However, we may not see the same large reductions in incidence in populations using these strategies in the “real world,” outside of a clinical trial. In clinical trial settings, participants are provided with ongoing prevention and support services including free condoms, HIV testing, STI testing and treatment, and intensive adherence and risk-reduction counselling. All of these services help to create “ideal” conditions that can maximize the impact of an HIV prevention strategy on HIV incidence. These new approaches may be less effective outside of a clinical trial if they are not provided in combination with these additional support services.

Community-based organizations will play an important role in packaging new prevention approaches with additional strategies and supports. This will include:

• Adherence support to help people integrate these strategies into their daily lives and use them consistently.
• Education on how to use the strategies correctly, including information on their advantages and disadvantages compared to existing approaches and the factors that may reduce their effectiveness.
• HIV prevention and risk-reduction counselling to help people understand their HIV transmission risk while they are using a prevention technology and to help them adopt additional HIV and STI prevention strategies. This will also need to include linkages and referrals to other services needed by people at risk of HIV infection and transmission.

Again, community-based research can play an important role in providing  insight into how people are using these strategies in the “real world” and the barriers to using these strategies consistently and correctly.

The role of CBOs and CBR in the changing HIV prevention landscape

The HIV prevention landscape is changing and CBOs have an important role to play in ensuring NPTs are used by the “right” people, at the “right” time, in the “right” context, and in the “right” way.

However, there is an increasing concern that the introduction of these technologies, particularly those based on antiretrovirals, will “medicalize” HIV prevention and reduce the role of CBOs in the response to the HIV epidemic. This is because most “biomedical” NPTs can only be obtained from a healthcare provider and need to be combined with ongoing medical services, such as laboratory and clinical monitoring, HIV testing (in the case of PEP and PrEP), and STI testing and treatment. Therefore, the worry is that these new “biomedical” approaches will shift the setting of HIV prevention from the community to the clinic.

In reality, it’s clear that these new prevention approaches are not exclusively “biomedical” and need to be packaged with several non-clinical services in order to prevent risk compensation, promote their appropriate uptake and sustained use, and ensure they are effective outside of a clinical trial setting. These are services that many healthcare providers do not have the time, knowledge, or expertise to provide effectively and, therefore, represent a gap that CBOs need to fill.

Moving forward

Dr. Kevin Fenton of the Centers for Disease Control and Prevention (CDC) in the United States gave a presentation at the 2012 International AIDS Conference in Washington where he discussed the implications of this new research for CBOs. He called upon CBOs to adapt to the changing HIV prevention landscape by:

• Learning new skills (improving their science base and understanding of clinical trial results).
• Developing new clinical alliances (improving their ties with organizations and institutions where these prevention technologies can be obtained).
• Providing new clinical and prevention services (offering HIV and STI testing, adherence support, and risk-reduction support).
• Promoting the uptake and correct use of these technologies (developing accurate, tailored, context-specific information; ensuring messages reach their target populations through a variety of different mechanisms, such as peer–peer outreach).

James Wilton is the Coordinator of CATIE’s Biomedical Science of HIV Prevention Project, he can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it. .

Interviews by James Wilton: This article first appeared in Prevention in Focus, a publication of CATIE.

Une version française est disponible ici. 

We asked three people about the challenges of explaining risk to their clients and patients.

Jody Jollimore—Program Manager, Health Initiative for Men, Vancouver

Riyas Fadel—M.A. candidate, Sexology, Université du Québec à Montréal

Mona Loutfy—Infectious Diseases Specialist, Women's College Hospital; Research Director, Maple Leaf Medical Clinic; Associate professor, University of Toronto

Jody Jollimore

What are the major challenges in communicating risk?

The overarching challenge is how to communicate risk without confusing or discouraging people.

One challenge is trying to communicate risk without putting a number on it. The public often wants risk to be communicated as a percentage (such as 2%) or a ratio (such as a 1 in 50 probability of HIV transmission). However, it’s very difficult to communicate risk as a number and these ratios can easily be misunderstood. For example, a person could understand this ratio to mean that they can have anal sex without a condom 50 times before they get HIV when, in fact, they could be the guy who does it once and gets HIV or the guy who does it 600 times and doesn’t get HIV.

Another challenge is how to communicate the many variables that need to be considered, such as the viral load of the HIV-positive partner, whether either partner has sexually transmitted infections (STIs), the window period, how often someone is getting tested, and how much one partner trusts the other(s). All these things can affect transmission significantly but are not easily measured or quantified. The information is complicated and can discourage someone from trying to reduce their risk.

What are the limitations of current approaches to communicating risk?

Most current models for communicating risk group activities into “low-risk” and “high-risk” categories. For example, unprotected oral sex and protected anal sex are normally considered low-risk and all unprotected anal sex is assigned to the high-risk category. However, at the Health Initiative for Men, we don’t think this approach is nuanced enough to reflect the recent research or the complex and exciting sex lives of gay men. Gay guys know that risk is more than just “low” or “high” and that other variables can influence their risk of HIV transmission. We feel that this approach doesn’t give guys a lot of options to choose from to reduce their risk. Not all guys are able, or want, to reduce their risk by engaging in “low-risk” activities and not all unprotected anal sex is the same.   

What are your solutions?

At HIM we have developed a risk communication model that includes a risk calculator—it can be found on our “Do the Math: Calculate Your Risk” website. We opted to expand the “low-risk” and “high-risk” model to include more categories, including “no or very low,” “low,” “moderate,” “high” and “very high” risk. The model uses several factors to assess risk, including the type of sex they are having (oral or anal), the position they are assuming (top or bottom), the HIV status of both partners (poz, neg or unknown) and whether condoms are used. Using the statistics from the ManCount survey, we felt that these were the variables that gay men were most commonly using to make decisions and also those that people know the most about.

This approach gives gay men more options to reduce their risk. Instead of simply telling people that all unprotected anal sex is high-risk, we opted to say that it is more risky than oral sex and protected anal sex, but less risky if you are a top or with a same-status partner.

Our model doesn’t provide numbers, but it is based on absolute risk percentages calculated in a mathematical modelling study titled “Reducing the risk of sexual HIV transmission: quantifying the per-act risk for HIV on the basis of choice of partner, sex act, and condom use” (Varghese et al 2001), published in the journal Sexually Transmitted Diseases. The numbers in this study informed our “Do the Math” model and were used to assign different activities to a risk category.

We didn’t provide the numbers from this study in our model because we don’t feel that communicating risk as percentages and ratios is the most effective way of translating probability information to the average gay guy. Even those of us who are well versed in statistics can struggle to understand them, specifically the difference between absolute risk and relative risk and how the two can interact. You can look at the numbers but the more you look into all the factors used to calculate them, the more you realize how far from reality they are and how they have little meaning in the “real world.”

What are the limitations of your approach?

The main weakness of our model is its simplicity. Although it is more nuanced than other models, it doesn’t consider factors such as antiretroviral treatment, acute HIV infection, STIs, dates of testing, and trust. These factors were difficult to integrate into the calculator for various reasons.

In the case of viral load, there are still gaps in the research, particularly among gay men, and the messages are different depending on the context (for example for poz guys vs. neg guys, gay guys who go the bathhouse vs. guys in monogamous serodiscordant relationships). Since these factors need a more detailed explanation and there is no simple message that applies to everyone, they are discussed at length in the text on the website but were not integrated into our risk calculator.  

In the end, the risk calculator was a bit of a compromise. We asked ourselves “Do we want to get something out there or produce nothing because it’s too complicated?” We opted to take on the challenge and start a community dialogue about risk.

Riyas Fadel

In your experience, how do different people understand risk differently and how does this affect the choices they make?

People understand risk subjectively and this makes it a challenge to explain and communicate risk.

Frontline workers tend to use categories such as “high-risk,” “low-risk” and “negligible risk” to assess a person’s risk of HIV transmission. However, people understand these categories in different ways. For one person “high-risk” might be unprotected oral sex and for another person “high-risk” is unprotected anal sex. It’s all subjective and often depends on whether the person is more cautious in general or more of a risk-taker.

What I find interesting is that a person’s view of risk is not set in stone, it can change based on their personal experiences with risk. For example, if a person remains uninfected after engaging in activities they consider high-risk, their idea of what is risky may change. On the other hand, if a person engages in what they consider a low-risk activity and becomes infected, then their perception may change in the opposite way. This works the same with other types of “risk,” for example, driving fast.

How a person feels about the consequences of taking risks also plays a big role in how a person evaluates risk. Some people may not be concerned about becoming infected with a sexually transmitted infection because they figure that treatment is available, whereas others are very concerned.

Also, some people place a greater value on taking risks than others. We live in a society where it’s not uncommon for people to have a “no risk, no gain” attitude. For a long time research used the term “sensation-seeking” to characterize some gay men’s risk-taking profiles. These are men who go to bathhouses, raves and parties, do drugs and have multiple partners—all stuff based on sensation. Some of them seek out certain types of activities, which can include unprotected sex, because it has a certain meaning for them.  

However, I have met a lot of “sensation seekers” who always use condoms or other prevention strategies and have a very good “sexual health” approach to their safer sex practices, so these categories aren’t always useful and can be stigmatizing. We need to figure out what’s going on with someone instead of simply labelling them. As frontline workers, our approach should be focused on a person’s overall sexual health and how they can adopt, and maintain, strategies that help them reach their goals.

We now have a much better understanding of the biology of HIV transmission. How has new research made communicating risk more challenging?

The new research has complicated things in some ways. We have learned a lot about the dynamics of HIV transmission and, at the same time, about how we need to do a better job of explaining the research to clients. Communicating risk was already complicated and it’s only getting more complicated with all the relative risk numbers and statistics emerging from the research on treatment as prevention, post-exposure prophylaxis, pre-exposure prophylaxis and microbicides.

The new research can make frontline workers uneasy because the condom message was so simple and now the messages are so much more complex. Clients are learning about the research from a variety of sources and asking very specific questions, such as: “If being on treatment and having an undetectable viral load reduces the risk of HIV transmission by 96% and condoms reduce the risk by 98%, then is being on treatment only 2% worse than condoms?” Frontline workers are having to unpack this information with clients and it’s challenging.

While things are getting more complicated, it’s also a very exciting time to be working in HIV prevention. We now have a much larger box of prevention tools to discuss with clients.

How do you help a client assess their risk and develop safer sex strategies?

When frontline workers use statistics, they need to be very clear about what the numbers mean. Numbers can be a great tool to help people conceptualize risk but can also be very confusing. Every time I give a number or a statistic from a study, such as a 96% risk reduction or a 3% risk of transmission per act, I always contextualize it and ensure that people understand how these numbers were calculated and what they mean. When I do this, many clients realize that numbers are not really the answer they are looking for.

I also find it interesting and useful to explore the client’s perceptions of risk. I start by asking a client about a sexual activity and ask them to place it somewhere on a risk continuum. Next, I ask the client about the sexual activities they engage in and whether they consider them more or less risky than those already on the continuum. I find that this approach works well because it gives the client a clearer picture of what relative risk is and how different activities relate to each other.

Also, as much as a person understands the risks and doesn’t want to become infected, there is a point before or during a sex act when people sometimes don’t put into practice what they know or what they planned to do. We focus too much on saying “use a condom” or “you have the data, you should know better” and don’t talk enough about the context or the structures someone has to navigate to put what they know into practice.

When I did outreach work helping people evaluate risks and develop a strategy for safer sex practices, I would ask clients to make a list of things they like to do sexually and the context in which they would happen. We would then explore how they try to reduce their risk and how that changes depending on the context. I would also ask them about things they really want to do but have never done and things they have never done and would never do. The goal of these exercises is to prepare clients to negotiate safer sex in different contexts.

Dr. Mona Loutfy

Can you tell me a bit about the situations in which you counsel patients about risk? And how do those situations differ from one another?

As a physician, I counsel individuals and couples who are sexually active and considering unprotected sex, for example, serodiscordant couples that want to conceive, or same sex male couples considering unprotected sex. I also counsel sexual assault victims who are considering taking HIV post-exposure prophylaxis (PEP).

Assessing HIV risk in the context of sexual assault can be more challenging than the consensual sex situation because there are often more unknown risk factors and variables. For example, the HIV status of the assailant may be unknown to the victim. If the assailant is known to be HIV-positive, it’s difficult to know if they were on treatment and had a fully suppressed viral load.

These unknowns need to be built into the risk assessment. If the HIV status is unknown, then we refer to the prevalence rate of HIV in the community of that area. For example, in the case of men between the ages of 19 and 50 in Toronto, the prevalence rate is 1%. The risk that the assailant was HIV-positive can then be multiplied by the risk posed by the kind of sexual act involved (receptive or insertive anal, vaginal or oral sex). Other risk factors that need to be considered include whether there were any STIs and whether there was any bleeding or tearing.

If the sex was consensual , then more of the risk factors are known. If I am counselling a serodiscordant couple that wants to conceive, I generally know the HIV status of both partners, whether there are any STIs, and the viral load of the HIV-positive partner. I frequently counsel serodiscordant couples on safer conception and how being on treatment and having a fully suppressed viral load can reduce the risk of HIV transmission through unprotected sex.

How do you communicate the risk of HIV transmission when the viral load is undetectable?

In the context of undetectable viral load, I go through the data and explain the Swiss Statement as well as the findings from the HPTN 052 study and from other cohort studies. I tell them that I can’t say there is zero risk when the viral load is undetectable, but that if you look at the studies among serodiscordant couples where the HIV-positive partner meets the conditions set out in the Swiss Statement, there have been no documented HIV transmissions.

Unfortunately, all these studies were done among heterosexual couples and therefore we don’t know how much these research findings apply to same-sex male couples. I tell same-sex couples that the data likely transfers to some degree, but trauma and tearing is more common with anal sex and can increase the risk.

When counselling, I use qualitative expressions to describe risk—for example, I say the risk is “very very low” when the viral load is undetectable and the couple is heterosexual. I don’t usually use numbers because we don’t necessarily know what the numbers mean, particularly for same-sex male couples. I also tend to avoid talking about relative risk because I don’t think the average person understands this concept very well.

We now have a much better understanding of the biology of HIV transmission. How has this research changed your approach to communicating risk?

I am fairly conservative about risk as a result of my personality and my role as a healthcare provider. However, with the new research on viral load and HIV transmission, I am relaxing a bit in my counselling. Instead of recommending that couples always use condoms, there are certain situations in which I can tell couples that the risk of HIV transmission is very low without condoms.

We have so much more data out there now, which is great and it has made things easier in some ways for counselling. However, with every additional study that comes out, we have more answers but also more questions. We will never know everything and there will always be some unknowns.

What are some of the tools you use to help someone assess their risk?

Regardless of the situation, I always start my counselling by saying that we are going to talk about probabilities and that it’s very hard to ever say that there is “no risk” of transmission. For most people, risk can be a hard concept to wrap their head around.

The two major things I do to help people understand their risk and make informed decisions are to make sure I take the time with the clients and make sure that I know the data. I try to book longer appointments for counselling sessions or make sure that I schedule them at the end of the day, so that we don’t have a restricted amount of time. It’s important to take the time to answer a client’s questions until they don’t have any more.

It’s also important to know the data very well so I can answer all these questions. I conduct some of the research myself so I can say I really know the data. For example, I recently led a research team in a systematic review of the evidence to better understand the risk of HIV transmission when the viral load of the HIV-positive partner is undetectable. This review has been submitted to a peer-reviewed journal for publication.

Another study we are currently conducting is called the Ontario HIV Pre-Conception Cohort Study. We are enrolling HIV-positive individuals who are interested in getting pregnant or parenting, with or without partners. Part of this study is aimed at gaining a better understanding of how people conceptualize risk and what risks they are willing to take.

Related article

To read the feature article on communicating risk, see Certainly uncertain: Challenges in communicating HIV risk.

About the author

James Wilton is the Project Coordinator of the Biomedical Science of HIV Prevention Project at CATIE. James has an undergraduate degree in Microbiology and Immunology from the University of British Columbia.

This article by James Wilton first appeared in Prevention in Focus, a publication of CATIE.

Une version française est disponible ici. 

Service providers working in HIV prevention are often asked by their patients and clients about the risk of HIV transmission from an exposure to HIV through sex. What do the latest studies tell us about this risk? And how should we interpret and communicate the results?

Challenges in calculating a number

It isn’t easy for researchers to calculate the risk of transmission from an exposure to HIV through sex. To do this effectively, a group of HIV-negative individuals need to be followed over time and their exposures to HIV—both the number of times they are exposed and the types of exposure—need to be tracked.  

As you can imagine, accurately tracking the number of times a person is exposed to HIV is very difficult. Researchers ask HIV-negative individuals enrolled in these studies to report how many times they have had sex in a given period of time, what type of sex they had, how often they used condoms and the HIV status of their partner(s). Because a person may have trouble remembering their sexual behaviour or may not want to tell the whole truth, this reporting is often inaccurate.

Furthermore, a person does not always know the HIV status of their partner(s). For this reason, researchers usually enroll HIV-negative individuals who are in stable relationships with an HIV-positive partner (also known as serodiscordant couples). Researchers can then conclude that any unprotected sex reported by a study participant counts as an exposure to HIV.

Several studies have aimed to estimate the average risk of HIV transmission from a specific type of unprotected sex (for example, vaginal/anal/oral; insertive/receptive). Due to the difficulties of calculating this risk, these studies have produced a wide range of numbers. To come up with a more accurate estimate for each type of unprotected sex, some researchers have combined the results of individual studies into what is known as a meta-analysis.

All exposures are not equal

The results of several meta-analyses suggest that some types of sex carry on average a higher risk of HIV transmission than others. Below are estimates from meta-analyses that have combined the results of studies conducted in high-income countries. For types of sex where meta-analysis estimates do not exist, numbers from individual studies are provided.

Anal sex 

A meta-analysis exploring the risk of HIV transmission through unprotected anal sex was published in 2010.1 The analysis, based on the results of four studies, estimated the risk through receptive anal sex (receiving the penis into the anus, also known as bottoming) to be 1.4%. (This means that an average of one transmission occurred for every 71 exposures.) This risk was similar regardless of whether the receptive partner was a man or woman.

No meta-analysis estimates currently exist for insertive anal sex (inserting the penis into the anus, also known as topping) but two individual studies were conducted to calculate this risk. The first, published in 1999, calculated the risk to be 0.06% (equivalent to one transmission per 1,667 exposures).2 However, due to the design of the study, this number likely underestimated the risk of HIV transmission. The second study, published in 2010, was better designed and estimated the risk to be 0.11% (or 1 transmission per 909 exposures) for circumcised men and 0.62% (1 transmission per 161 exposures) for uncircumcised men.3

Vaginal sex

A meta-analysis of 10 studies exploring the risk of transmission through vaginal sex was published in 2009.4 It estimated the risk of HIV transmission through receptive vaginal sex (receiving the penis in the vagina) to be 0.08% (equivalent to 1 transmission per 1,250 exposures).

A meta-analysis of three studies exploring the risk from insertive vaginal sex (inserting the penis into the vagina) was estimated to be 0.04% (equivalent to 1 transmission per 2,500 exposures).4

Oral sex

No meta-analysis estimates exist for oral sex (vaginal or penile) because too few good-quality studies have been completed. This is because it is difficult to find people whose only risk of HIV transmission is unprotected oral sex. A review of the studies that are available was published in 2008 and concluded that vaginal and penile oral sex pose a “low but non-zero transmission probability.”5

In the three studies aimed at calculating the risk of HIV transmission from one act of oral sex, no transmissions were observed among three different populations—lesbian serodiscordant couples, heterosexual serodiscordant couples and single gay men—who reported unprotected oral sex as their only risk for HIV transmission. However, these studies enrolled only a small number of people and followed them for only a short period of time, which may explain the lack of HIV transmissions and makes it impossible to conclude that the risk from oral sex is zero.

Interpreting the numbers—what additional information needs to be provided? 

Some clients may see these numbers and think their risk of HIV transmission is low. Therefore, caution is needed when interpreting them. If these numbers are provided to clients, they should be accompanied by information that helps shed light on why the risk may be higher than it seems. 

Transmission can occur after one exposure.

It is important to emphasize that a person could become infected from having unprotected sex once or a person could have unprotected sex many times and not become infected, regardless of how low or high the risk per exposure is.

A risk of 1% would mean that an average of one infection would occur if 100 HIV-negative people were exposed to HIV through a certain type of sex. It does not mean that a person needs to be exposed 100 times for HIV infection to occur.

These are estimates of average risk in the absence of biological factors that increase risk.

The numbers in the table above are rough estimates. They are averages and do not represent the risk from all exposures to HIV through a certain type of sex.

We know that no two exposures to HIV are exactly the same. Research shows that, in addition to the type of sex that led to the exposure, several factors can increase or decrease the risk that an exposure to HIV leads to infection. These include the presence of sexually transmitted infections (STIs), a high viral load, a man being uncircumcised, a woman menstruating, other bleeding and activities that can cause tearing and inflammation, such as rough sex, longer sex, douching, enemas before anal sex, and tooth brushing, flossing or dental work before oral sex. Each exposure to HIV carries a unique risk of transmission that depends on the type of sex and a combination of biological factors.

The risk of HIV transmission may be much higher than these averages if biological risk factors are present. For example, research shows that STIs and some vaginal conditions, such as bacterial vaginosis, can increase the risk of HIV transmission by up to 8 times.6,7,8 As a result, the risk of an HIV-negative woman becoming infected through unprotected receptive vaginal sex could be closer to 1% (1 transmission per 100 exposures) if she has a vaginal STI.  

We also know that for every 10-fold increase in viral load, the risk of HIV transmission increases by 2 to 3 times.9,10 Research suggests the extremely high viral load during acute HIV infection (the first few weeks after becoming infected with HIV) can increase the risk of HIV transmission by up to 26-fold.11,12 Therefore, unprotected sex with an HIV-positive person who has acute HIV infection could carry a transmission risk of up to 2% (the equivalent of 1 transmission per 50 exposures) for receptive vaginal sex and over 20% (equivalent to 1 transmission per 5 exposures) for receptive anal sex.

The more exposures, the greater the risk.

Although the risk of HIV transmission from a single exposure may seem low to some people, this risk increases over multiple exposures. In other words, a person who is exposed to HIV more often has a greater overall risk of HIV transmission than someone who is exposed less often.

If a woman has unprotected vaginal sex 100 times with a man who is HIV-positive, the cumulative risk is approximately 10% and may be higher if biological risk factors are present.

Differences in risk

Information on how risky certain types of unprotected sex are compared to others may help people make more informed decisions about the type of sex they are having.

Based on the meta-analysis estimates, we can draw several conclusions

• Receptive anal sex carries a much higher risk of HIV infection than receptive vaginal sex. Research shows that the risk of HIV transmission from receptive anal sex is up to 18 times higher than from receptive vaginal sex.
• Receptive anal sex is riskier than insertive anal sex. Research suggests the risk of HIV transmission from receptive anal sex is 3 to 23 times higher than from insertive anal sex.
• Receptive vaginal sex is riskier than insertive vaginal sex.The risk from receptive vaginal sex is about twice as high as that from insertive vaginal sex.
• It is unclear exactly how much less risky oral sex is compared to vaginal and anal sex.

Conclusion

Although it’s impossible to provide a client with their exact risk of HIV transmission from an exposure, some studies have managed to estimate an average risk for different types of sex. It's important to provide clients with additional information to help them interpret the findings. Here are some key messages:

1. These numbers are

• challenging to calculate and should therefore be considered rough estimates
• do not represent the risk of transmission from all exposures to HIV
• represent the average risk of transmission in the absence of biological factors that can increase risk (such as STIs and a high viral load)
• are most relevant to people in stable monogamous serodiscordant relationships

2. These numbers may seem low but

• HIV transmission can occur after a single exposure
• the risk may be much higher if certain biological risk factors, such as STIs or a high viral load, are present
• as more exposures to HIV occur, the overall risk of transmission increases
• most HIV transmissions in Canada occur through unprotected anal and vaginal sex

3. There are several ways of reducing the risk of HIV transmission from an exposure, such as post-exposure prophylaxis (PEP), using antiretroviral treatment to reduce viral load, circumcision, treatment for STIs and vaginal conditions, or engaging in lower-risk activities.

4. There is no way to reduce the risk of HIV transmission to zero after an exposure occurs. Taking measures to avoid an exposure in the first place (for example, through the correct use of condoms or other barrier methods, or by ensuring a partner has the same HIV status) can help reduce the overall risk of HIV transmission.

References

 1. Baggaley RF, White RG, Boily M-C. HIV transmission risk through anal intercourse: systematic review, meta-analysis and implications for HIV prevention. International Journal of Epidemiology. 2010 Aug;39(4):1048–63.

 2. Vittinghoff E, Douglas J, Judson F et al. Per-contact risk of human immunodeficiency virus transmission between male sexual partners. American Journal of Epidemiology. 1999 Aug 1;150(3):306–11.

 3. Jin F, Jansson J, Law M et al. Per-contact probability of HIV transmission in homosexual men in Sydney in the era of HAART. AIDS. 2010 Mar 27;24(6):907–13.

4. a. b. Boily M-C, Baggaley RF, Wang L et al. Heterosexual risk of HIV-1 infection per sexual act: systematic review and meta-analysis of observational studies. Lancet Infectious Diseases. 2009 Feb;9(2):118–29.

 5. Baggaley RF, White RG, Boily M-C. Systematic review of orogenital HIV-1 transmission probabilities. International Journal of Epidemiology. 2008 Dec;37(6):1255–65.

 6. Ward H, Rönn M. Contribution of sexually transmitted infections to the sexual transmission of HIV. Current Opinion in HIV and AIDS. 2010 Jul;5(4):305–10.

7. Atashili J, Poole C, Ndumbe PM et al. Bacterial vaginosis and HIV acquisition: a meta-analysis of published studies. AIDS. 2008 Jul 31;22(12):1493–501.

 8. Cohen CR, Lingappa JR, Baeten JM et al. Bacterial vaginosis associated with increased risk of female-to-male HIV-1 transmission: a prospective cohort analysis among African couples. PLoS Medicine. 2012 Jun;9(6):e1001251.

9. Wawer MJ, Gray RH, Sewankambo NK et al. Rates of HIV-1 transmission per coital act, by stage of HIV-1 infection, in Rakai, Uganda. Journal of Infectious Diseases. 2005 May 1;191(9):1403–9.

10. Baeten JM, Kahle E, Lingappa JR et al. Genital HIV-1 RNA predicts risk of heterosexual HIV-1 transmission. Science Translational Medicine. 2011 Apr 6;3(77):77ra29.

 11. Wawer MJ, Gray RH, Sewankambo NK et al. Rates of HIV-1 transmission per coital act, by stage of HIV-1 infection, in Rakai, Uganda. Journal of Infectious Diseases. 2005 May 1;191(9):1403–9.

 12. Hollingsworth TD, Anderson RM, Fraser C. HIV-1 transmission, by stage of infection. Journal of Infectious Diseases. 2008 Sep 1;198(5):687–93.

 About the author

James Wilton is the Project Coordinator of the Biomedical Science of HIV Prevention Project at CATIE. James has an undergraduate degree in Microbiology and Immunology from the University of British Columbia.