The Supreme Court of Canada (R. v. Cuerrier, [1998] 2 SCR 371) ruled that there is a legal duty to disclose HIV-positive status to sexual partners before having sex that poses a "significant risk" of HIV transmission. Non-disclosure viatiates consent constituting fraud.

However, “significant risk” has not been clearly or consistently defined and prosecutions for non-disclosure prior to oral sex and sex with condoms have taken place.

• R. v. Nduwayo: no legal duty to disclose HIV-status if condoms were used
• R v. Imona-Russell: duty to disclose if sex was “unprotected”
• R. v. Mabior, 2008 MBQB 201 (Can. Man.): disclosure of HIV status required even with condom use if viral load is detectable), reversed by R. v. Mabior, 2010 MBCA 93 (Can. Man. C.A.): no duty to disclose if condom used or undetectable viral load
• R. v. Mekonnen, 2009 ONCJ 643 (Can. Ont.): disclosure required even with condom use
• R v. Aziga, (4 April 2009), Hamilton CR-08-1735: convicted on aggravated sexual assault charge based on unprotected oral sex
• R. v. Mekonnen, 2009 ONCJ 643 (Can. Ont.): deciding that vaginal intercourse with a condom but without HIV disclosure is an aggravated sexual assault, without considering evidence of risk of HIV transmission
• R. v. Mabior, 2008 MBQB 201 (Can. Man.): requiring disclosure of HIV status even with condom use if viral load is detectable), reversed by R. v. Mabior, 2010 MBCA 93 (Can. Man. C.A.) (reversing lower court conviction)

Additionally, a futher ruling by the Supreme Court of Canada (R. v. Williams, [2003] 2 SCR 134) suggested that a person may have a legal duty to disclose their HIV-positive status before having sex that poses a significant risk of transmission even if they know their sexual partner also has HIV; and a person who knows there is a risk that he or she has HIV (but has not received an actual HIV-positive diagnosis) may have a legal duty to tell sexual partners about this risk before having unprotected sex.

As a result, substantial confusion amongst people living with HIV, healthcare workers and legal practitioners exists regarding when the duty to disclose arises. (See Mykhalovskiy E. The problem of "significant risk": Exploring the public health impact of criminalizing HIV non-disclosure. Social Science & Medicine (2011) (In further reading)

In February 2012, the Supreme Court of Canada revisited the above rulings during two appeals (R v. Mabior; R v 'DC') in order to re-examine whether Cuerrier remains valid in the light of inconsistent lower court decisions regarding what constitutes a "significant risk" of HIV transmission in the context of sex, especially when the person with HIV wears a condom and/or has an undetectable viral load due to effective antiretroviral therapy.  A decision is expected by Autumn 2012.  

Below are Factums (statements of the facts of a case) from the Manitoba Prosecution Service - arguging that all potential sexual exposure, regardless of condom use or viral load should require disclosure - and from the interveners: Canadian HIV/AIDS Legal Network, HIV & AIDS Legal Clinic (Ontario), Coalition des organismes communautaires québécois de lutte contre le sida, Positive Living Society of British Columbia, Canadian AIDS Society, Toronto People With AIDS Foundation, Black Coalition for AIDS Prevention and Canadian Aboriginal AIDS Network - arguing that advances in science now require the Court to rule more clearly on what constitutes "significant risk" and to agree that there is no requirement to disclose if a  condom is used or the person with HIV has an undetectable viral load.

A short audio report following the appeal hearing from Xtra Magazine's Marcus McCann can be heard below.