Understanding the factors affecting HIV transmission is crucial for safeguarding sexual health. It's important to be aware of the risk factors and protective measures, as well as the significant role of viral load in HIV transmission.
Unprotected Anal Intercourse and HIV Transmission Risk
For individuals engaging in unprotected anal intercourse with an HIV-positive partner whose viral load is fully suppressed, the risk of infection is effectively zero. It's worth noting that maintaining an undetectable viral load is a key factor in this equation.
If HIV is not fully suppressed due to ineffective treatment, anal intercourse without condoms becomes a high-risk route for sexual HIV transmission for both the receptive and insertive partner. Several factors can increase the risk of transmission, including sexually transmitted infections and recent HIV infection in the positive partner.
It's important to highlight that when the HIV-positive partner is taking effective antiretroviral treatment and maintains an undetectable viral load, the risk of HIV transmission through anal intercourse is negligible.
PARTNER-2 Study Findings
The PARTNER-2 study closely monitored 783 male couples in which the HIV-positive partner had an undetectable viral load, and they engaged in unprotected anal intercourse. After 1,596 couple-years of follow-up and approximately 77,000 instances of unprotected anal intercourse, no HIV transmission occurred. Researchers concluded that the risk of HIV transmission under these conditions was virtually zero.
However, when the viral load is detectable, condomless anal intercourse becomes a highly efficient method of HIV transmission. The degree of risk varies depending on multiple factors.
Transmission Risk for Insertive and Receptive Partners
While there is a common belief that insertive partners ("tops") are at very low risk of HIV infection, it's essential to clarify that being the insertive partner in unprotected anal sex remains a high-risk activity. The per-act risk for the insertive partner is comparable to that of the male (insertive) partner in vaginal sex.
Receptive partners ("bottoms") face a risk of HIV transmission due to exposure to the virus in semen and pre-seminal fluids. The rectal tissue is delicate and can be easily damaged, providing the virus with direct access to the bloodstream. Even without tissue damage, rectal tissue contains cells susceptible to HIV infection.
The insertive partner also faces a risk of infection due to high levels of HIV in rectal secretions and blood from rectal tissues. In particular, the virus can enter the insertive partner through the urethra and under the foreskin. Studies estimate that condomless receptive anal intercourse carries approximately ten to twelve times greater risk of infection compared to insertive anal intercourse.
For each condomless act with an untreated HIV-positive partner, the risk of infection is estimated at 1.38% (one in 72 chance) for the receptive partner and 0.11% (one in 909 chance) for the insertive partner. However, the risk may be significantly higher if the HIV-positive partner has recently acquired the infection.
Recent Infection and HIV Transmission Risk
During the first few weeks or months after an individual contracts HIV, their viral load is typically high, making them highly infectious. This early phase, known as primary infection, significantly raises the risk of transmission, particularly in the first two and a half months. During this period, viral load levels are elevated. People often remain unaware of their infection, unintentionally exposing their sexual partners to HIV. Timely diagnosis and treatment are essential in reducing the risk of transmission.
Sexually Transmitted Infections (STIs)
Most STIs, especially those causing ulcers, such as herpes simplex 2 (HSV-2), syphilis, gonorrhea, and chlamydia, increase the risk of HIV acquisition in HIV-negative partners during vaginal intercourse. In people living with HIV who are not on treatment, STIs lead to increased genital shedding of HIV, increasing the risk of transmission. However, STIs do not elevate the risk of transmission in individuals taking effective HIV treatment with an undetectable viral load.
Poppers and Rectal Douching
Using poppers during unprotected, receptive anal intercourse more than doubles the risk of HIV infection, as it relaxes the anal sphincter muscles and increases blood flow to rectal tissues. Rectal douching can damage the rectal lining and remove protective naturally occurring bacteria, increasing the risk of HIV infection.
Rectal Bleeding and Male Circumcision
Rectal bleeding can heighten the risk of HIV transmission and may be caused by conditions like haemorrhoids, STIs, or sexual activities. Male circumcision may offer some protection, but only for men who exclusively take the insert
Effective protective measures include:
1.The HIV-positive partner taking effective HIV treatment and maintaining an undetectable viral load.
2.The HIV-negative partner using pre-exposure prophylaxis (PrEP).
3.Consistent condom use and the use of lubricant.
4.Post-exposure prophylaxis (PEP) as an emergency measure.
Understanding these factors is essential for making informed decisions about sexual health and minimizing the risk of HIV transmission. Regular testing, communication, and access to preventive methods are key components of maintaining sexual health.