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HIV in Ontario > Transmission


Only five bodily fluids contain enough HIV to transmit the virus: blood, semen (including pre-cum), rectal fluid, vaginal fluid and breast milk. HIV can only be transmitted when virus in one of these fluids gets into the bloodstream of an HIV-negative person, either through broken skin or by passing through the mucous membranes (the “wet” tissues of the body).

This fact sheet describes how HIV transmission happens through: sexual activity; sharing/reusing needles or other equipment used to inject drugs, or for tattooing or piercing; and during pregnancy, childbirth and infant feeding.

What is necessary for HIV transmission to occur?

For HIV transmission to occur there are three necessary components: a fluid, a route and an activity or event. Sufficient virus in a fluid containing HIV needs to get into the body of an HIV-negative person. This can happen only through a limited number of activities.

The amount of virus in the blood and other bodily fluids of a person with HIV is known as the viral load. It is measured as the number of copies of the virus per millilitre of blood (copies/ml). Most viral load tests used in Canada cannot detect HIV in the blood if there are fewer than 40 to 50 copies/ml, though some newer tests can detect as few as 20 copies/ml. People who have a lower concentration of the virus than these thresholds are said to have an undetectable viral load. When a person takes HIV treatment consistently, their viral load can become undetectable within about three to six months. Having an undetectable viral load greatly lowers or eliminates the chance of passing HIV. A person with HIV will have a higher viral load right after contracting the virus, which can be reduced to the undetectable level if they take effective treatment.


There needs to be a fluid that contains enough HIV to cause infection. The lower the viral load, the lower the chance of passing HIV. When the viral load is undetectable it significantly reduces the chance of passing the virus.

Only five bodily fluids can contain enough HIV to transmit the virus:

  • blood
  • semen (including pre-cum)
  • rectal fluid
  • vaginal fluid
  • breast milk


HIV can only be passed when virus in one of the five fluids gets into the body of an HIV-negative person through one of the following routes:

  • a mucous membrane (the wet linings of the body), such as the opening of the penis, the foreskin, the vagina or the rectum; or
  • a break in the skin, such as when someone shares needles used to inject drugs or someone has a needlestick injury.


There needs to be an activity or event that brings the fluid and route together for HIV transmission to occur. The activities/events that can potentially transmit HIV are:

  • unprotected sexual activity (such as anal or vaginal sex, giving oral sex and sharing sex toys)
  • sharing/reusing needles or other equipment used to inject drugs or used for tattooing or piercing, and accidental needlestick injury
  • pregnancy, childbirth and infant feeding (for transmission to a fetus or infant)

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