In a 9-0 ruling, the top court updated a landmark 1998 decision that made it a crime if HIV carriers did not reveal their status when there was a significant risk of transmission to a sexual partner.
The court ruled Friday that the "realistic possibility of transmission of HIV is negated" provided the carrier of the virus has a low viral load and a condom is used during sexual intercourse. Otherwise, HIV carriers have to disclose their status to their partners.
The court also said the new ruling does not preclude the law from adapting to future advances in medical treatment and to circumstances where different risk factors are at play.
Under the previous law, HIV-carriers who didn't tell partners they had the virus could be charged with aggravated sexual assault. The maximum penalty is life in jail.
Appeals from Quebec, Manitoba cases
The Supreme Court ruled on two separate cases from Quebec and Manitoba in which charges brought against those who failed to disclose their condition were overturned by appeals courts.
One of the cases involves Clato Mabior, who has since been deported to South Sudan, who had sex with nine women, including a 12-year-old girl, between 2004 and 2005 after being diagnosed HIV-positive.
Mabior was sentenced to 14 years in prison after being convicted of aggravated sexual assault in six of nine of the cases, but he was acquitted of the remaining three because the judge ruled that his low level of HIV and the fact he wore a condom negated his duty to inform the women.
The Manitoba Court of Appeal later overturned four of his convictions saying not all of the women were exposed to "significant risk."
The Supreme Court said Friday that three of Mabior's convictions should be restored because he did not use a condom, and one acquittal was upheld because he did use a condom in that sexual encounter and had a low viral load.
Mabior's lawyer welcomed the ruling.
"The court has struck a balance, given that the Crown attorney's position in both jurisdictions as I understood it was that in all circumstances, there was a positive duty to disclose one's HIV status," said Amanda Sansregret. "Quite frankly, that would be such a broad use of the criminal law."
The other case involves a woman from Quebec who had unprotected sex with her partner without first informing him that she was HIV-positive. A publication ban prevents naming the woman, who is referred to in Supreme Court documents only as "D.C."
The woman was initially found guilty of sexual assault and aggravated assault, but that conviction was later overturned by the Quebec Court of Appeal on the basis that her viral load was undetectable during the period that the charges covered.
The Supreme Court upheld the woman's acquittal.
Interveners dislikes ruling
A lawyer for the B.C. Civil Liberties Association, which was an intervener in the case, was disappointed that the Supreme Court decision did not go further.
"My client's position is that the criminal law is a harsh tool that should be reserved for the most morally blame-worthy cases," said Michael Feder.
"What you're talking about here is a vulnerable, marginalized group of people who are going to be forced to go around volunteering to anyone with whom they're going to have sexual contact, that they belong to that vulnerable, marginalized group," he said.
Richard Elliott, the executive director of the Canadian HIV/AIDS Legal Network, which also intervened in the case, said the decision was not a good one for people living with HIV.
His group's position is that either a low viral load or the use of a condom should be the required test to avoid being prosecuted, but not both, as the top court said in Friday's ruling.
"We know from the science now that if either you use a condom or you have a low viral load, the risk of transmission is extraordinarily small," he said.
Jessica Whitbread, who contracted HIV from a former boyfriend more than a decade ago, said she thought Friday's ruling was a step forward — at first. But upon closer examination, she said this ruling could make her the criminal.
"I can still have a vindictive lover say that I did or didn't use a condom," she told CBC News. "It still becomes 'he said, she said. he said, he said.' …That can still play a very important role in the courts."