Transmission - KnowledgeConnect PAN

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Transmission is how HIV (or another viruses or bacteria) moves from one person who has it to another person who can get it. This happens through specific pathways like certain body fluids entering the body which allows the virus to pass between people. This step is part of what’s called the “chain of infection,” which explains how infections spread from one person to another.

HIV is transmitted through specific body fluids like blood, semen, vaginal and rectal fluids, and breast milk. The main modes of transmission are unprotected sexual contact, sharing needles or injection equipment, from mother to child during pregnancy, birth or breastfeeding, and through blood transfusions where blood is not screened. HIV is not spread through everyday contact such as hugging, kissing, sharing food, or mosquito bites.

Unprotected Sexual Contact Transmission

It is important to distinguish between different forms of sexual contact in terms of which ones carry a higher risk of HIV transmission compared to others. In harm reduction services, communicating accurate information about transmission helps community members make informed decisions.

Unprotected anal sex (especially being in the receptive/bottom position) carries the highest risk of HIV transmission because the lining of the rectum is thin and can allow the virus to enter the body more easily. Vaginal sex carries a lower, but still present risk, as HIV can enter through the vaginal lining or the penis. Oral sex carries very low risk, because the mouth is less vulnerable to HIV transmission, especially when there are no cuts or sores.

What makes an activity higher risk is the combination of body fluids that can carry HIV (like blood, semen, or vaginal fluids) and how easily those fluids can enter the body through sensitive tissues or openings.

AIDSmap provides a data table that outlines activity and the associated risk-per-exposure.

HIV Transmission and Mode of Drug Use Compared

The information and statistics in this section are shared with respect and purpose. They are not meant to shame or judge, but to support informed choices, reduce harm, and improve health outcomes. Sharing accurate information can help reduce harm and support people’s health.

Injection Drug Use (IDU)

The Estimated Risk of Transmission

Each instance of injection with a syringe that has been exposed to HIV carries an estimate risk of 0.63% to 0.84%. To put it a different way, roughly 1 out of every 150 times a used needle is shared with someone who has HIV could lead to transmission, but it’s not a guarantee.

The Pathway of Transmission

HIV is transmitted when blood containing the virus enters the bloodstream of another person by sharing needles, syringes, or “works” (cookers, filters, water).

Inhalation Use (smoking)

The Estimated Risk of Transmission

The biological risk of HIV transmission from sharing a pipe is negligible to zero. Transmission via inhalation equipment is extremely rare to negligible.

The Pathway of Transmission

Although low to negligible, a pathway can be created where blood is present caused by cuts, burns, sores, or cracked lips while sharing a pipe.

Secondary Risk

While HIV risk is significantly lower, sharing pipes can lead to the transmission of hepatitis C or other infections if there are sores, cuts, or burns on the lips/mouth.

Things that Reduce the Risk

Using your own pipe or mouthpiece and avoid sharing when there are visible sores, cuts, or burns on lips/mouth.

While BC is a leader in harm reduction, the availability of safer smoking supplies can be a challenge in many SURR areas. CLICK to read more.

Harm reduction infrastructure in BC was built around injection-based and “safer inhalation” kits are more newly added to inventory.
There are more safe injection sites compared to inhalation sites due to more limited number of facilities offering inhalation. Specialized ventilation can be expensive and difficult to install.
Vending machine initiatives faced significant pushback and were paused or restricted in many regions.