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Sexual transmission: risks and prevention


In Africa, Europe, and the US, researchers have followed heterosexual couples in which one of the partners was infected with HIV, asked them about their sexual behaviour, and observed how many partners became infected. From these studies, the estimated average risk to contract HIV through vaginal sex without a condom with an HIV-infected partner is 0.05% to 0.11% per coital act, or about once per 900 to 2,000 coital acts (see table, below). Generally, less than 10% of HIV-positive men or women with HIV-negative spouses transmit HIV to their spouses in a year, even with continued unprotected (without condom) sex.

Table: Estimated risks to get HIV from an HIV-infected sex partner

Exposures (without a condom)
Estimated risk
Vaginal sex 0.05%-0.11%
Anal intercourse, receptive 0.5%-3%
Anal intercourse, insertive 0.07%
Oral sex, receptive 0.01%-0.04%*
Oral sex, insertive 0.005%*

Sources: references [1-6]  * There is some controversy about transmission efficiency through oral sex. Campo and colleagues report no transmissions after 19,000 events reported by 135 discordant heterosexual couples.[7] On the other hand, Wood and colleagues emphasize data are not adequate to estimate the risk, suggesting it could be higher than rates in the above table.[8]

Many factors influence the efficiency of sexual transmission. For example: When someone has a new infection, semen or vaginal fluids are have more virus than after a few months. Risk increases an estimated 2-4 times if either partner has a genital ulcer or sexually transmitted disease (STD).[9] In addition, risk appears to vary from person to person for reasons no one understands.

If a man is HIV-positive, unprotected anal sex (penis in anus) is much more dangerous for the woman than vaginal sex (see table, above).

Preventing HIV from sex

Methods to prevent HIV transmission through sex are changing over time, and some methods may not be available everywhere. We encourage you to consult other sources for the latest and local advice.

Preventing HIV from spouses and other long-term partners: With more HIV testing, millions of couples in Africa are learning of HIV infection in one or both partners. While an HIV-positive test is bad news, knowing that a husband or wife is HIV-positive allow couples to take care of the HIV-positive partner and to protect the HIV-negative partner and new children.

Discordant couples can protect the HIV-negative partner by getting antiretroviral treatment (ART) for the HIV-positive partner and checking from time-to-time to see if the viral load is suppressed. ART reduces transmission risk by more than 90%. Discordant couples can also use condoms. An option for couples who want to get pregnant is pre-exposure prophylaxis (PrEP) with antiviral drugs for the HIV-negative partner. Couples with HIV in one or both spouses will be able to live, birth, and raise children like anyone else.

Preventing HIV acquisition from non-spousal partners: The risk to contract HIV from a non-spousal sexual partner depends on the risk associated with the specific sexual acts (see table, above) and on the risk a partner is HIV-positive. With more testing, including self-testing, regular non-spousal partners can see if anyone is HIV-positive, so they know if they need to take precautions. For non-regular partners, good advice to avoid getting HIV is summarized in a simple acronym – ABC: Abstain or Be faithful to one partner; if not, use a Condom. In addition, treating any STDs that you have reduces your risk to get HIV if you have unprotected sex. Our one caveat is that injections to treat STDs may be risks for HIV, so you should take care to ensure safe STD treatment (see Injection section).

Preventing HIV for men who have sex with men (MSM): MSM are at high risk to get HIV from receptive anal sex (see table). When MSM are both insertive and receptive partners, they can both get HIV and pass it on to other men through anal sex, leading to high percentages of MSM with HIV infection. Condom use can stop HIV transmission through anal as well as vaginal sex. Men taking ART are much less infective. HIV-negative men can take antiretrovirals for pre-exposure prophylaxis — before and after sexual contact — reducing their risk to get HIV by as much as 90%.


1. CDC. Antiretroviral postexposure prophylaxis after sexual, injection drug-use, or other nonoccupational exposure to HIV in the United States: recommendations from the U.S. Department of Health and Human Services. MMWR 2005; 54 (No. RR-2): 1-20. Available at: (accessed 28 January 2019).

2. Gray RH, W awer MJ, Brookmeyer R, et al. Probability of HIV-1 transmission per coital act in monogamous, heterosexual, HIV-1-discordant couples in Rakai, Uganda. Lancet 2001; 357: 1149-1153.

3. Mastro TD, Kitayaporn D. HIV type 1 transmission probabilities: estimates from epidemiological studies. AIDS Res Hum Retroviruses 1998 (suppl 3): S223-S227.

4. Varghese B, Maher JE, Peterman TA, et al. 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. Sex Transm Dis 2002; 29: 38-43.

5. Vittinghoff E, Douglas J, Judson F, et al. Per-contact risk of human immunodeficiency virus transmission between male sexual partners. Am J Epidemiol 1999; 150: 306-311.

6. DeGruttola V, Seage GR III, Mayer KH, Horsburgh CR Jr. Infectiousness of HIV between male homosexual partners. J Clin Epidemiol 1989; 42: 849-856.

7. del Romera J, Marincovich B, Castilla J, et al. Estimating the risk of HIV transmission through unprotected orogenital sex. AIDS 2002; 16: 1996-1297. Abstract available at: (accessed 28 January 2019).

8. Wood LF, Chahroudi A, Chen H-L, et al. The oral mucosa immune envirnment and oral transmission of SIV/HIV. Immunol Rev 2013; 254. Available at: (accessed 28 January 2019).

9. Rottingen J-A, Cameron DW, Garnett GP. A systematic review of the epidemiologic interactions between classic sexually transmitted diseases and HIV: how much is really known? Sex Transm Dis 2001; 28: 579-587.

31 responses to “Sexual transmission: risks and prevention

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  5. Vincent September 28, 2013 at 9:06 am

    Plz i need a help, i had unprotected sex with hiv positive woman,3times the sameday,on june 30,i dont no that she is hiv +,i went for a test on july 5th 2013,which is 34day but my result was negetive,and Doctor told me to come back and sheck again after 3month can it change from negetive to positive after 3 month i ve being having many symtoms like leg and hand pain,fever,and strest,

  6. Simon Collery September 28, 2013 at 1:10 pm

    Hi Vincent, sorry to hear you are worried that you may have been exposed to HIV. However, it sounds like you are already in touch with a doctor, so they should be in the best position to give you advice. If you don’t wish to discuss it with your doctor you should go to see another type of health professional, preferably one whose experience is in HIV and/or sexually transmitted infections. Some doctors and health professionals will answer questions over the phone, by email, perhaps even on Skype, etc. I hope that helps and I wish you all the best. By the way, if you are ever in the same position again you should see a health professional as soon as possible, within 72 hours. They can prescribe a course of antiretroviral drugs which should substantially reduce your risk and the treatment is called ‘post-exposure prophylaxis’ or PEP.

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  8. hitendra April 10, 2014 at 2:10 pm

    I need help besically I m 29 yrs male from India and sorry for english. Las week I had gone to massage parlour, while massaging I had unprotected sex with that girl initially she was not readdy bu when I had given extra tip her then she agreed and we done in standing position no oral no sucking by me and her also.Exposure time was less than 1 min and it was my 1st time I m curcumcised. Then i was scared and asked her and she replied that she has nothing. There is no any sore on my penis while exposure and no symptoms till yet. However, I m scared pls give valuable teply

  9. hitendra April 10, 2014 at 2:14 pm

    I need help besically I m 29 yrs male from India and sorry for english. Las week I had gone to massage parlour, while massaging I had unprotected sex with that girl initially she was not readdy bu when I had given extra tip her then she agreed and we done in standing position no oral no sucking by me and her also.Exposure time was less than 1 min and it was my 1st time I m curcumcised. Then i was scared and asked her and she replied that she has nothing. There is no any sore on my penis while exposure and no symptoms till yet. However, I m scared pls give valuable reply as possible as early

  10. Simon Collery April 10, 2014 at 5:48 pm

    Thank you for your message. The best thing to do is go to a sexually transmitted infection clinic, or any health facility that provides these services, and explain what happened, They should be able to give you good advice and make various tests. You should do this at once, though, don’t delay.

  11. allan April 11, 2014 at 8:10 pm

    hi. am a male aged26. i had sex with HIV+ girl. we did twice and that was Wendnesday and friday. doctors gave me perp on monday of the other week. I would like to ask & know, the first act of Wednesday was out of 72 hours. bt the act of friday was within72 hours since i started perp. what is the rate of possibility of becoming safe?

  12. Simon Collery April 12, 2014 at 1:03 pm

    Hi Allan, thanks for your comment. However, I am not qualified to give you medical advice. I can only suggest that you see a doctor or other qualified health professional, perhaps the one who gave you the post exposure prophylaxis. The risks listed above are only estimates and depend on many other factors, which you could discuss with a health professional.

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  15. Anonymous September 26, 2014 at 10:31 am

    my frien having unprotected sex with a married woman. She has sex with both my friend and her husband. Is there any health risk to either of us?

    • Simon Collery September 26, 2014 at 10:41 am

      Thank you for your question. Your friend is at risk if anyone s/he is having sex with has HIV or any sexually transmitted infection, as stated in the information above. Using a condom should give a lot of protection and it is also preferable to know the HIV status of anyone you are having sex with, protected or unprotected. If you have doubts you and your friend should see a counselor and perhaps take a HIV test, so you’ll be sure.

  16. alihramadhan September 27, 2014 at 10:29 pm

    hello, i am a male, i had sex with hiv +girl, i came to realize sh wz+ after we visited vct, 2my side i waz negative bt bcz i had already practiced unsafe sex the doctors advice me to stat taking truvada /prep , am worried cz since i finished truvada its now4 months, i went4 another test after using truvada a mean after60 days and the results came negative, i want to know if the false negative can last for 120 days or what is the excactly days for the hvi virus to be seen after exposure? Becasuse am experiencing musle pain

  17. Simon Collery September 28, 2014 at 9:27 am

    Details available on this site are highly generalized so you would need to see a specialist to assess your precise risks. It’s better to see a specialist immediately than continuing to worry about these matters, they should be able to put your mind at rest!

  18. rahul June 19, 2015 at 6:42 pm

    I have sex with my gf.. We were both virgin..and we have sex first time in life.we are intimated taking any there any problem that I had to notice??

    • Simon Collery June 21, 2015 at 5:09 pm

      Hi Rahul, being a virgin does not guarantee that you or your partner are HIV negative. In most countries, it is unlikely, but there’s never any harm in being tested for all sexually transmitted infections before you have sex, even for the first time. HIV, herpes, human papilloma virus, hepatitis C, even syphillis, and several other diseases associated with sexual transmission can also be transmitted non-sexually. You might also like to avoid pregnancy, so it’s a good idea to use condoms or some other reliable birth control method.

  19. Atozzio Nygaxx September 3, 2015 at 7:19 pm

    Am circumcised and had unprotected sex with my partner who’s status is not well known by me. I had it more than 5 times in one day without using a condom… My question is that can I get HIV if that person has the virus?

  20. Simon Collery September 4, 2015 at 3:58 am

    Thank you for your question. Yes, having unprotected (condomless) sex with your partner is a risk for HIV if your partner is infected, circumcision will not protect you. Your risk also depends on whether you or your partner were the receptive (bottoms) partner, or whether you swapped around. You should consult an experienced HIV counselor for advice if you are worried about being infected, and about infecting others.

    • Atozzio Nygaxx September 4, 2015 at 5:31 am

      Ok thank you, but in the first place i used to condoms then did the rest without it… Does the virus automatically enter through semen or after some time. Coz i was not having it continuously but was waiting for some time

  21. Atozzio Nygaxx September 4, 2015 at 5:31 am

    Ok thank you, but in the first place i used to condoms then did the rest without it… Does the virus automatically enter through semen or after some time. Coz i was not having it continuously but was waiting for some time

  22. Simon Collery September 4, 2015 at 1:14 pm

    I think the best thing to do is talk to a counselor or doctor and they can assess your risk.

  23. Atozzio Nygaxx September 5, 2015 at 5:30 am

    Ok thanks very much again, I will try to do what u have said

  24. Atozzio Nygaxx September 11, 2015 at 9:58 am

    A week ago, i had sex with a girl i ddnt know her status well. At first, i used a condom twice and ended up doing it without a condom for 4 times. When i woke up, i met a friend and he told me that the girl sleeps with a lot of guys but i was doubting, after hearing the news, i felt so depressed and shocked. After 4 days, i started feeling headache. Each time in the evening, i feel body weakness like malaria but when i wake up, i feel fine. Yesterday, i woke up early but the veins in my eyes where paining like pulling… I have never experienced eye pains in my age unless when I was 5, 6, 7… I also do exercise before I go to sleep so I dnt know if they are symptoms or it’s just another sickness because it’s too early. So I was asking if u can help me if they are HIV symptoms or not?

  25. Simon Collery September 12, 2015 at 7:15 pm

    Thank you for your email, the best thing to do is get advice from a professional HIV counselor or other health professional and get a HIV test as soon as possible.

  26. Anonymous May 11, 2017 at 12:59 pm

    Am am a female aged 20 ..i just found that my boyfriend is cheating onme on me ..and we both went to the clinic to get tested for hiv and then the result come out and my boyboyfriend tested positive and mine was negative ..but now the problem is my boyfriend doesn’t wantto take ttreatment he always makes acquires.i realy lv him his the father of my child i didn’t leave after his status but suported him wat scares me is that am i putting my self at rick. Because since after birthwe never used condom n nw after finding out abt his status we were having sex without condom but ejaculate out side my vigina or sometime wear condom when ready to ejaculate .soo now after having sex my vulva sore and i have little spores that are too painful is that mean am already infected. ..plz i realy need an advaice bcz my boyfriend doesn’t wnna take abt situation n his status

    • Simon Collery May 11, 2017 at 1:34 pm

      I think it’s very important that, wherever you are, you go to see a doctor or to an STI clinic or a HIV clinic, get tested and get advice. Don’t trust your future to something you might find on the web, alone, this is for the benefit of your child as well. Get professional help and don’t depend on the web.

  27. October 22, 2018 at 2:18 am

    Sexual transmission: risks and prevention | Don’t Get Stuck With HIV
    Parajumpers Jakke norge

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