In a major 9-0 ruling Friday, the high court specified those two key conditions, clarifying the rules on whether it is a crime for people with extremely low levels of HIV to withhold their condition from their sex partners.
The court said it was reflecting the medical advances in treating the virus that causes AIDS since it first ruled on the issue in 1998 and left open the possibility of adapting to future changes in science in medicine.
The Supreme Court ruled on two separate cases, from Manitoba and Quebec, updating its landmark 1998 ruling on the subject.
The court ruled 14 years ago that people with HIV must inform their sex partners of their condition, or face a charge of aggravated sexual assault, which carries a maximum life sentence.
Now, that duty to disclose has been removed as a long as the HIV carrier has a "low load" of the virus and wears a condom.
"On the evidence before us, a realistic possibility of transmission is negated by evidence that the accused's viral load was low at the time of intercourse and that condom protection was used," Chief Justice Beverley McLachlin wrote on behalf of the court.
"However, the general proposition that a low viral load combined with condom use negates a realistic possibility of transmission of HIV does not preclude the common law from adapting to future advances in treatment and to circumstances where risk factors other than those considered in the present case are at play."
The ruling was a partial victory for HIV/AIDS activists who have argued that the 1998 ruling sowed confusion and was applied unevenly. They wanted the decision struck down, but argued that, in the alternative, the court should at least refine that ruling to reflect new medical advances.
Friday's decision still wasn't enough for a coalition of groups, which said the court's ruling would undermine public health efforts and stigmatize people living with the illness and amounted to "a cold endorsement of AIDS-phobia."
"They don’t need the constant threat of a criminal accusations and possible imprisonment hanging over their heads," said a statement from the Canadian HIV/AIDS Legal Network. "Similarly, people not living with HIV need to be empowered to accept responsibility for their own health and not proceed under a false sense of security that the criminal law will protect them from infection."
The Supreme Court squarely addressed — and firmly rejected — that argument.
"The only 'evidence' was studies presented by interveners suggesting that criminalization 'probably' acts as a deterrent to HIV testing," McLachlin wrote.
"The conclusions in these studies are tentative and the studies were not placed in evidence and not tested by cross-examination. They fail to provide an adequate basis to justify judicial reversal of the accepted place of the criminal law in this domain."
The Supreme Court rejected the argument that there should be a blanket law requiring people with HIV to disclose their condition under every circumstance. Prosecutors from both provinces argued that HIV carriers have a duty to inform their partners regardless of the risk.
The court did not set an actual level for an acceptably low viral load, but offered a description, based on the evidence of the case.
"As noted by the court of appeal, the transmissibility of HIV is proportional to the viral load, i.e. the quantity of HIV copies in the blood," the decision said. "The viral load of an untreated HIV patient ranges from 10,000 copies to a few million copies per millilitre.
"When a patient undergoes antiretroviral treatment, the viral load shrinks rapidly to less than 1,500 copies per millilitre (low viral load), and can even be brought down to less than 50 copies per millilitre (undetectable viral load) over a longer period of time. This appears to be scientifically accepted at this point, on the evidence in this case."
The court was considering two cases, one of which involved Clato Mabior of Winnipeg, who was diagnosed with HIV in January 2004. He had sex with nine different women between February 2004 and December 2005 without telling them he was HIV positive.
None of the women contracted the disease.
After Mabior was partly successful before Manitoba's appeal court, the Supreme Court was left to rule on four remaining convictions of aggravated sexual assault.
He was found to have low viral load with three of the complainants but did not use a condom. Those convictions were upheld.
But with one other woman, the justices were satisfied that he had used a condom and because he met the second factor — a low viral load — his conviction on that count was set aside.
For Mabior, the ruling is academic — he was deported to South Sudan in February.
Nonetheless, his lawyer welcomed the decision.
"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."
In the second case, involving a Quebec soccer mom, the Supreme Court affirmed an earlier appeal court ruling that struck down her conviction for aggravated assault and sexual assault.
The woman, who cannot be identified, had sex with a man she met at her son's soccer game in 2000 without disclosing her illness. She had been taking anti-retroviral drugs after an HIV diagnosis nine years earlier.
"Here low — indeed undetectable — viral load was established," the Supreme Court concluded.
When the woman told the man about her illness, he left her, but returned to have a four-year, live-in relationship during which they had protected and unprotected sex. The man remained AIDS-free.
They broke up when the woman accused the man of assault, a crime for which he was convicted.
Afterwards, the man complained to police about their first sexual encounter, and her failure to disclose her illness.
The woman was tried and convicted of aggravated assault and sexual assault, but the convictions were overturned by the Quebec Court of Appeal, a decision the Supreme Court upheld.
At trial, the woman maintained a condom was used, but the man disputed that.
The trial judge didn't believe either of them.
But the trial judge ultimately concluded that the woman was lying and that no condom was used. He based his conclusion on a note from the woman's doctor.
The note said that the woman told her doctor that the condom broke. The trial judge inferred that the woman was in fact lying to cover up the fact no condom was used.
The Supreme Court reversed that finding, saying that the "speculative edifice the trial judge built on a single hearsay note made seven years before the trial does not constitute evidence that no condom was used."
That meant that the prosecution failed to prove that a condom was not in fact used. Combined with her undetectable level of the virus, she could not be convicted.