Many patients see me understandably anxious and want me to help them analyze their risk of getting HIV. I usually divide my discussion into 3 parts:
- Source Risk
- Transmission Risk
- Patient Risk
The person you have been exposed to must have HIV in order for you to be at risk of getting HIV. Also, the person must have a detectable viral load.
People who are living with HIV and on treatment with an undetectable viral load cannot pass HIV on to someone else. This concept of Undetectable = Untransmissable (U=U) has been proven as fact.
Most of my patients do not know their partner’s status. It is also not possible to tell if a person has HIV or not based on symptoms. And therefore we have to make the assumption that the person has HIV. Because if we assume the person does not have HIV, there is really no need to have a discussion on HIV risk.
The likelihood of your partner having HIV can be estimated from the HIV prevalence of the geographic region you are in.
You can use this website to access the WHO HIV Country Profile reports to get an idea of the HIV prevalence rate in different countries. Remember that these are population statistics and are different from the actual risk of the particular individual you have been exposed to having HIV.
In summary, most of the time there is very little we can discuss about the source risk and have assume that the person has HIV and a detectable viral load to proceed with the discussion.
If your partner is living with HIV and has an undetectable viral load (<50 copies per ml) you really do not have to be worried about getting HIV from this person.
Transmission Risk
The risk of getting HIV depends on the particular sex act.
The highest risk sex act is receptive anal intercourse with ejaculation.
I have detailed below the estimated risk of getting HIV according to 3 of the most trusted and respected Health Authorities. Namely – US CDC, British HIV Association (BHIVA) and Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine (ASHM).
These statistics are for condom-less sex acts with a partner who is HIV positive and has a detectable viral load.
US CDC
- Blood Transfusion – 9250 per 10,000 exposures
- Needle Sharing during Injection Drug Use – 63 per 10,000 exposures
- Needlestick – 23 per 10,000 exposures
- Receptive anal intercourse – 138 per 10,000 exposures
- Receptive penile-vaginal intercourse – 8 per 10,000 exposures
- Insertive anal intercourse – 11 per 10,000 exposures
- Insertive penile-vaginal intercourse – 4 per 10,000 exposures
- Receptive oral intercourse – Low
- Insertive oral intercourse – Low
- Biting, Spitting, Sharing sex toys – negligible
BHIVA
- Receptive anal intercourse – 1 in 90
- Receptive anal intercourse with ejaculation – 1 in 65
- Receptive anal intercourse with no ejaculation – 1 in 170
- Insertive anal intercourse – 1 in 666
- Insertive anal intercourse not circumcised – 1 in 161
- Insertive anal intercourse and circumcised – 1 in 909
- Receptive vaginal intercourse – 1in 1000
- Insertive vaginal intercourse – 1in 1219
- Semen splash to eye – < 1 in 10,000
- Receptive oral sex – < 1 in 10,000
- Insertive oral sex – < 1 in 10,000
- Blood transfusion – 1 in 1
- Needlestick injury – 1 in 333
- Sharing injecting equipment – 1 in 149
- Human bite – < 1 in 10,000
ASHM
- Receptive anal intercourse with ejaculation – 1 in 70
- Receptive anal intercourse with withdrawal – 1 in 155
- Shared needles and other injecting equipment – 1 in 125
- Insertive anal intercourse uncircumcised – 1 in 160
- Insertive anal intercourse circumcised – 1 in 900
- Receptive vaginal intercourse – 1 in 1250
- Insertive vaginal intercourse – 1 in 2500
- Receptive or insertive oral intercourse – Unable to estimate risk – extremely low
- Needlestick injury – 1 in 440
The Sanford Guide – 2014
- Female to male transmission – 1 in 700 to 1 in 3000
- Male to female transmission – 1 in 200 to 1 in 2000
- Male to male transmission – 1 in10 to 1 in 1600
- Fellatio – unknown
- Transfusion of infected blood – 95 in 100
- Needle sharing – 1 in 150
- Needlestick injury – 1 in 3
From the numbers above I think you can immediately see a few key takeaways.
First, the risk of HIV transmission from a sexual exposure is not as high as what most people think it is. Even for the highest risk sex act which is receptive anal intercourse, the risk is at the low single digit percentages.
Second, there is a huge range in estimated risks even between reports from respected Health Authorities that have obviously done a lot of research to publish these numbers. This is because it is obviously extremely difficult to find quality data to accurately estimate the risk of HIV transmission. Also because there are so many variables in a sexual encounter. It is reasonable to expect every encounter’s risk to be different. So these risk statistics are at best a close estimate.
Third, it is very rare for a Doctor to be absolutely sure that a patient is completely not at risk. However, Doctors can know that the risk is so low as to render it insignificant. That is why we use the words “negligible risk”. What that really means is there is no need for the patient to take active steps to negate the risk like taking HIV PEP.
So commonly patients are left in a frustrating position where Doctors tell them they are at risk but we don’t know exactly what the risk is but it is probably very low. The thing about facing a life changing disease like HIV is that even if the risk is 1 in 10,000, it is understandable for people to think what if they were the 1.
Patient Risk
Conditions in the patient (i.e. the person at risk of getting HIV) also increases the HIV risk.
The following data is taken from the Sanford Guide 2014. The numbers are Relative Risk numbers. Relative Risk is a ratio of probability. A RR of > 1 means the risk is increased.
Conditions that increase the risk of HIV sexual transmission are:
Female to male transmission
- Lack of circumcision – RR: 5.4 – 8.2
- Genital Ulcers – RR: 2.6 – 4.7
- Sex during menses – RR: 3.4
- Genital Herpes – RR: 6- 16.8
Male to female transmission
- Oral contraceptive – RR: 2.5 – 4.5
- Gonococcal Cervicitis – RR: 1.8 – 4.5
- Candida Vaginitis – RR: 3.3 – 3.6
- Genital Ulcers- RR: 2.0 – 4.0
- Bacterial Vaginosis – RR: 1.6
The most glaring statistic from this is that the lack of circumcision greatly increases the risk of getting HIV. In fact, from the BHIVA and ASHM statistics, it is also reported that uncircumcised men who engage in insertive anal intercourse have a higher risk of getting HIV compared to circumcised men.
Genital ulcers are defects in the skin and mucosa. Having these would compromise the natural skin barrier and make it easier for HIV to enter the body.
In conclusion
Analyzing your HIV risk can be useful in several aspects.
If you are at a high risk for HIV and your exposure was < 72 hours ago, you should see your Doctor immediately and speak to your Doctor about HIV PEP.
Knowing your estimated risk of getting HIV hopefully has given you some peace of mind. However, the only way to know if you have been infected with HIV or not is to get a HIV test.
Getting tested is especially important if you develop any symptoms that may suggest an acute HIV infection.
Have a question? Please put it in the comments section below.