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About the Data

About "Know the HIV Risk"

Every time an HIV-positive person has sex with an HIV-negative person, there is a chance the HIV-negative partner will get HIV. Some sex acts (such as, kissing, touching, and oral sex) have little to no HIV risk. You have a higher risk for getting or transmitting HIV through vaginal and anal sex.

Know the HIV Risk shows risks when one partner has HIV and the other partner doesn't. It gives you information for a single sex act at a time. You can change the settings on the tool to get information about a variety of sex acts.

Know the HIV Risk can give you different kinds of HIV risk information:

· It can give you the HIV risk for different sex acts

· It can also show which sex acts are riskier than others

Choosing to use protective factors (such as condoms, pre-exposure prophylaxis or PrEP, and antiretroviral therapy, or ART) can lower the HIV risk for each sex act.

Other risk factors (such as having an acute HIV infection or having another STD) can raise the HIV risk for each sex act.

About the Numbers

If you click on "Show numbers," you will see the number of times HIV could be transmitted for every 10,000 sex acts. The numbers may seem small, but they show the risk for one sex act. Your risk for getting or transmitting HIV increases every time you have sex with a discordant partner (a partner with a different HIV status).

Sexual activities

For example, Know the HIV Risk displays the number 138 for the risk of getting HIV from receptive anal sex. This represents that the risk for getting HIV from receptive anal sex (without condoms, PrEP, or ART) is about 138 per 10,000 sex acts. So, on average for an HIV-negative receptive partner, there is about a 1 in 72 chance of getting HIV for every act of receptive anal sex with an HIV-positive insertive partner. Within the messages of the HIV Risk Reduction Tool, the risk is displayed as 1 in 72.

This table outlines how the risk numbers for the other activities in Know the HIV Risk are displayed with the messages of the HIV Risk Reduction Tool.

Activity

Risk Displayed in Know the HIV Risk

Risk Displayed in the HIV Risk Reduction Tool Messages

Receptive Anal Sex

138

1 in 72

Insertive Anal Sex

11

1 in 909

Insertive Vaginal Sex

8

1 in 1250

Receptive Vaginal Sex

4

1 in 2500

Patel, P., Borkowf, C. B., Brooks, J. T., Lasry, A., Lansky, A., & Mermin, J. (2014). Estimating per-act HIV transmission risk: a systematic review. AIDS, 28(10), 1509-1519. doi: 10.1097/QAD.0000000000000298


Protective Factors

The three protective factors in Know the HIV Risk are condoms, PrEP, and ART. Each protective factor is assigned a numerical value that expresses the best estimates of effectiveness for that factor. The studies on the effectiveness of these factors use different methodologies and measures, and have been conducted in different populations. The numbers selected for use in Know the HIV Risk were chosen to try to minimize study differences; i.e. they are as comparable across activities and populations as possible. The numbers represent the best estimate of consistent use for each protective factor. They do not represent optimal use of these factors. If someone uses condoms, PrEP, or ART the right way every time, the effectiveness of these factors will be higher than what is reported in Know the HIV Risk.

ART

Protective Factor: ART for the HIV-positive partner

Activity

Risk Displayed in Know the HIV Risk

HIV Risk Reduction Estimate

Activity with Protective Factor

Receptive Anal Sex

138

96%

6

Insertive Anal Sex

11

96%

<.5

Insertive Vaginal Sex

8

96%

<.5

Receptive Vaginal Sex

4

96%

<.5

Cohen, M. S., Chen, Y. Q., McCauley, M., Gamble, T., Hosseinipour, M. C., Kumarasamy, N., . . . Team, H. S. (2011). Prevention of HIV-1 infection with early antiretroviral therapy. N Engl J Med, 365(6), 493-505. doi: 10.1056/NEJMoa1105243

· For insertive and receptive vaginal sex, Cohen and colleagues demonstrate that compared to delayed ART initiation, taking ART early reduces the risk of HIV transmission to an HIV-negative partner by 96%. Effectiveness is lower for persons who take ART don't stay virally suppressed. Effectiveness may be higher among persons who achieve and maintain viral suppression. (Read more about viral suppression in the HIV Risk Reduction Tool).

· For insertive and receptive anal sex, not direct evidence was found in the study from Cohen and colleagues for effectiveness of ART in reducing HIV transmission risk. Because there is no biologic or other reason to believe the effectiveness of ART would be lower for anal sex, the same estimate will be used for vaginal and anal sex until direct evidence is available for anal sex.

PrEP

Protective Factor: Daily PrEP for the HIV-negative partner

Activity

Risk Displayed in Know the HIV Risk

HIV Risk Reduction Estimate

Activity with Protective Factor

Receptive Anal Sex

138

92%

11

Insertive Anal Sex

11

92%

1

Insertive Vaginal Sex

8

90%

1

Receptive Vaginal Sex

4

90%

<.5

Grant, R. M., Lama, J. R., Anderson, P. L., McMahan, V., Liu, A. Y., Vargas, L., . . . iPrEx Study, T. (2010). Preexposure chemoprophylaxis for HIV prevention in men who have sex with men. N Engl J Med, 363(27), 2587-2599. doi: 10.1056/NEJMoa1011205

· For insertive and receptive anal sex, Grant and colleagues demonstrate that taking PrEP can reduce the risk of getting HIV from anal sex with an HIV-positive partner by 92%. In this study, PrEP use was shown by a laboratory-detected presence of the drug. Missing doses decreases the effectiveness of PrEP. Very high levels of adherence may increase effectiveness.

Baeten, J. M., Donnell, D., Ndase, P., Mugo, N. R., Campbell, J. D., Wangisi, J., . . . Partners Pr, E. P. S. T. (2012). Antiretroviral prophylaxis for HIV prevention in heterosexual men and women. N Engl J Med, 367(5), 399-410. doi: 10.1056/NEJMoa1108524

· For insertive and receptive vaginal sex, Baeten and colleagues demonstrate that taking PrEP can reduce the risk of getting HIV from vaginal sex with an HIV-positive partner by 90%. In this study, PrEP use was shown by a laboratory-detected presence of the drug. Missing doses decreases the effectiveness of PrEP. Very high levels of adherence may increase effectiveness.

Male Condoms

Protective Factor: Male Condoms for the insertive partner

Activity

Risk Displayed in Know the HIV Risk

HIV Risk Reduction Estimate

Activity with Protective Factor

Receptive Anal Sex

138

72%

39

Insertive Anal Sex

11

63%

4

Insertive Vaginal Sex

8

80%

2

Receptive Vaginal Sex

4

80%

1

Smith, D. K., Herbst, J. H., Zhang, X., & Rose, C. E. (2015). Condom effectiveness for HIV prevention by consistency of use among men who have sex with men in the United States. J Acquir Immune Defic Syndr, 68(3), 337-344. doi: 10.1097/QAI.0000000000000461

· For receptive anal sex, Smith and colleagues demonstrate that always using condoms with an HIV-positive partner can reduce the risk of getting HIV by 72%. The results are based on self-reported use, which may not be entirely accurate. Condom effectiveness is likely to be higher when condoms are used the right way every time during anal sex.

· For insertive anal sex, Smith and colleagues demonstrate that always using condoms with an HIV-positive partner can reduce the risk of getting HIV by 63%. The results are based on self-reported use, which may not be entirely accurate. Condom effectiveness is likely to be higher when condoms are used the right way every time during anal sex.

Weller, S., & Davis, K. (2002). Condom effectiveness in reducing heterosexual HIV transmission. Cochrane Database Syst Rev(1), CD003255. doi: 10.1002/14651858.CD003255

· For receptive and insertive vaginal sex, Weller and Davis demonstrate that always using condoms with an HIV-positive partner can reduce the risk of getting HIV by 80%. These results are based on self-reported use, which may not be entirely accurate. Condom effectiveness is likely to be higher when condoms are used the right way every time during vaginal sex.


Risk Factors

The risk factors in Know the HIV Risk are either partner having another STD, and acute infection. The risk factors are assigned numerical values that express the increase in risk for HIV transmission with the risk factor.

STDs

Risk Factor: STD infection for the HIV-negative partner

Activity

Risk Displayed in Know the HIV Risk

HIV Risk Estimate *

Activity with

Risk Factor

Receptive Anal Sex

138

2.65

366

Insertive Anal Sex

11

2.65

29

Insertive Vaginal Sex

8

2.65

21

Receptive Vaginal Sex

4

2.65

11

Hughes, J. P., Baeten, J. M., Lingappa, J. R., Magaret, A. S., Wald, A., de Bruyn, G., . . . Partners in Prevention, H. S. V. H. I. V. T. S. T. (2012). Determinants of per-coital-act HIV-1 infectivity among African HIV-1-serodiscordant couples. J Infect Dis, 205(3), 358-365. doi: 10.1093/infdis/jir747

· For receptive and insertive vaginal sex, Hughes and colleagues demonstrate that having an STD with sores increases the risk of getting HIV by a factor of 2.65 during sex with an HIV-positive partner.
*(NOTE: We used 2.6 in Know the HIV Risk.)

· For receptive and insertive anal sex, there are no empirical data providing a direct estimate for anal sex from Hughes and colleagues. Biological and epidemiological theories provide indirect evidence that having an STD with sores has similar effects on HIV risk for anal sex.

Risk Factor: STD infection for the HIV-positive partner

Activity

Risk Displayed in Know the HIV Risk

HIV Risk Estimate *

Activity with

Risk Factor

Receptive Anal Sex

138

2.58

356

Insertive Anal Sex

11

2.58

28

Insertive Vaginal Sex

8

2.58

21

Receptive Vaginal Sex

4

2.58

10

Gray, R. H., Wawer, M. J., Brookmeyer, R., Sewankambo, N. K., Serwadda, D., Wabwire-Mangen, F., . . . Rakai Project, T. (2001). Probability of HIV-1 transmission per coital act in monogamous, heterosexual, HIV-1-discordant couples in Rakai, Uganda. Lancet, 357(9263), 1149-1153. doi: 10.1016/S0140-6736(00)04331-2

· For receptive and insertive vaginal sex, Gray and colleagues demonstrate that having an STD with sores increases the risk of transmitting HIV by a factor of 2.58 during sex with an HIV-negative partner.
*(NOTE: We used 2.6 in Know the HIV Risk.)

· For receptive and insertive anal sex, there are no empirical data providing a direct estimate from Gary and colleagues. Biological and epidemiological theories provide indirect evidence that having an STD with sores has similar effects on HIV risk from anal sex.

Acute HIV Infection

Risk Factor: Acute HIV Infection for the HIV-positive partner

Activity

Risk Displayed in Know the HIV Risk

HIV Risk Estimate

Activity with

Risk Factor

Receptive Anal Sex

138

7.25

1001

Insertive Anal Sex

11

7.25

80

Insertive Vaginal Sex

8

7.25

58

Receptive Vaginal Sex

4

7.25

29

Wawer, M. J., Gray, R. H., Sewankambo, N. K., Serwadda, D., Li, X., Laeyendecker, O., . . . Quinn, T. C. (2005). Rates of HIV-1 transmission per coital act, by stage of HIV-1 infection, in Rakai, Uganda. J Infect Dis, 191(9), 1403-1409. doi: 10.1086/429411

· For receptive and insertive vaginal sex, Wawer and colleagues demonstrate that the risk of HIV transmission from an HIV-positive person in the early-stage of HIV infection (roughly the first 2.5 months after infection) is about 7.25 times greater than during the clinical latency phase HIV (Read about the stages of HIV infection and acute infection in the HIV Risk Reduction Tool).

· For receptive and insertive anal sex, there are no empirical data providing a direct estimate from Wawer and colleagues. It is biologically plausible for acute infection to have a similar effect on HIV risk from anal sex.

For more information on HIV risk and prevention estimates, visit http://www.cdc.gov/hiv/risk/estimates/index.html