TORONTO -- In deciding whether to uphold a man's sexual assault convictions, Ontario's top court has been asked to weigh whether the legal standard for disclosing HIV-positive status to sexual partners is more restrictive than what the scientific evidence calls for.

Lawyers for the appellant, who is identified in court documents by the initials N.G., are requesting that the Court of Appeal for Ontario overturn the man's convictions on three counts of aggravated sexual assault, or order a new trial based on evidence that proper condom use is enough to prevent transmission of HIV.

"It's clear the needle can be moved," Wayne Cunningham told the three-judge panel. "What we propose in this case is that fresh new evidence moves that needle."

But the Crown argued the appellant wants to move the needle too far, based on the assumption that everyone who wants to use a condom does so properly.

In the trial that ended in November 2017, court heard N.G. had used condoms in sexual encounters with three women who consented without knowing his HIV status.@

The trial heard the women would not have consented to sex had they known about their partner's HIV status.

As it stands, common law holds that a person with a low concentration of HIV in the blood does not need to inform sexual partners of their status if they use a condom.

The trial judge found condoms weren't enough in N.G.'s case because he did not have a low viral load, raising potential doubt about the possibility of transmission even with the contraceptive.

The trial judge also noted the sex was "in parks, in the bush and within the confines of a car," which he said were not optimal conditions for correct use.

But Cunningham argued Wednesday that new evidence shows condoms are enough to prevent transmission even in cases where a person's viral load is not low, and the common law should reflect that.

He pointed to two expert "consensus statements" on HIV transmission "in the context of criminal law" -- one from Canadian scientists, and one that is international.

"When used correctly and no breakage occurs, condoms are 100 per cent effective at blocking the transmission of HIV," reads the Canadian statement, signed by dozens of doctors and HIV researchers.

The statement notes the chance of contracting HIV from unprotected sex with a person with detectable levels of the virus is already low -- roughly eight in 10,000.

Cunningham argued a person with HIV using a condom for consensual sex should only be convicted of aggravated sexual assault if that contraceptive fails.

But Crown attorney Grace Choi argued that takes the wrong approach to the law.

"Whether there is a realistic possibility of HIV transmission should be a forward-looking estimate," she said, likening the approach to that of criminal law surrounding drunk driving and improper gun storage. In those cases, she said, the risky behaviour itself is the crime -- not the outcome of that behaviour.

Improper condom use is more common than some might like to acknowledge, Choi said, and it seldom happens on purpose.

"Human beings, being human, make mistakes," she said.

But the Canadian HIV/AIDS Legal Network, an intervener in the case, noted in a news release issued with two other organizations that the case speaks to a larger issue surrounding the stigma the virus presents.

"The injustice of criminalizing people living with HIV who correctly use condoms is compounded by the severe consequences of a conviction for aggravated sexual assault," it reads, listing prison time and designation as a sex offender among them.

"These are grossly disproportionate penalties for a sexual encounter that is otherwise consensual, and in which a person has taken a highly effective precaution that means either zero risk or at most a negligible risk of HIV transmission."

The panel of judges reserved its decision.

This report by The Canadian Press was first published Feb. 12, 2020.