Viral load describes the amount of HIV present in an individual’s bloodstream. In part, a patient’s viral load results are dependent on the sensitivity of testing technologies. Viral load suggests how well treatments are working and the current risk of damage to an individual’s immune system.
A lower viral load is also associated with reduced HIV sexual transmission risk. Findings from 3 key studies released over recent years have looked at how effectively anti-retroviral therapies (ARTs) prevent sexual transmission of HIV.
Current guidance from ASHM makes it clear that for people who take ART daily as prescribed and achieve and maintain a durable ‘undetectable viral load’ (HIV RNA < 200 copies/mL), the risk of sexual HIV transmission is eliminated. This crucial message has been popularised by the global campaign known as ‘Undetectable=Untransmittable’ – often referred to as ‘U=U’. See ASHM guidance on Undetectable = Untransmittable for healthcare workers.
Undetectable viral load #
According to ASHM, HIV treatments may reduce viral load to the point that it is undetectable in blood and this is typically achieved through HIV RNA < 20–50 copies/mL using current available testing technologies in Australia.
Evidence of reduced transmission #
Four major studies published in 2016 and 2017 provide robust support for the assertion that if someone takes ART daily, as prescribed, and achieves and maintains an undetectable viral load, this radically reduces the risk of sexually transmitting the virus to an HIV-negative partner.
The 4 studies are the HPTN052 study, the Partner 1 and Partner 2 studies, and the Opposites Attract study. These studies are described in the U=U: ASHM Guidance for Healthcare Professionals.
Legal implications #
The science around low and undetectable viral loads is relatively new. The way that Australian courts will engage and rely on evidence regarding a low or undetectable viral load is still emerging.
David J Carter has written about Australian consideration of viral loads in the criminal context. He notes that in Victoria, the case of Neal v The Queen [2011] VSCA 172provided opportunity for this consideration. He writes:
“The matter was raised in that case by way of the applicant’s statement to complainants (‘PC’, ‘MB’ and ‘SB’) that he maintained a UVL and could not transmit HIV on that basis. At various times, Mr Neal had, in fact, maintained a low viral load, and the Court was willing to accept arguments surrounding that fact as relevant … [to the question] in that particular case [of] whether the defendant subjectively ‘believed that he was capable of infecting others with HIV’. In relation to Neal the consideration by the court indicates that ‘The risk of transmitting HIV is no longer dependent upon HIV-positive status, but is instead dependent upon the viral load maintained at the relevant time.’ The Court in Neal accepted the contention that, in instances relating to the offence of attempted infection, the correct test is that the defendant must have believed or known that he or she ‘was infectious’, rather than that he or she ‘may be infectious.’ The advent of U=U means that a person’s status changes with regards to their being ‘infectious’. Legally speaking, this ‘new scenario of a changeable relationship between infection and infectiousness intersects with the criminal law as it comes into contact with a defendant’s knowledge or belief’.”
This means that in Australian jurisdictions where an HIV-related criminal offence relies upon the defendant having some subjective (actual) knowledge or foresight of a risk of transmission, if a defendant had achieved, and been aware of, an undetectable viral load, and had known that this meant that they posed no risk of transmission, this should work to support defence arguments.
Cases from international jurisdictions are varied. As David J Carter, writes:
‘In 2009, a Swiss court chose to quash a conviction for an endangerment-related offence in part because the Court accepted that the risk of transmission was negligible. However, other jurisdictions have not followed suit. The Canadian Supreme Court, for example, in R v Mabior and R v DC considered the requirement for individuals to disclose their HIV-positive status prior to sex. Building on the test from R v Cuerrier, the Court found that a ‘significant risk’ of HIV transmission triggers the legal duty to disclose, and that a significant risk is present unless a person has low viral load and uses a condom. In so doing, the Court found that non-disclosure was a correct basis for criminal punishment in the context of a ‘realistic possibility of transmission’. The Court confirmed that only condom use combined with ART reduces this risk enough to preclude liability, and this remains the threshold that applies in relation to the duty to disclose in that jurisdiction. Canada is not alone in this approach. Following two years of review, the Norwegian Law Commission concluded that a UVL is not a valid defence to a person with HIV having unprotected sex whether or not transmission results, although it may be a consideration in sentencing’.
Recent Australian research indicates that criminal prosecution of HIV-related offences continues in many jurisdictions. Recent cases include 19 cases on the public record. Notably, excluding so-called ‘spitting and biting cases’, approximately half of these cases relate to transmission occurring in heterosexual sexual contexts, a profile at odds with the general picture of HIV transmission in Australia. Additionally concerning is that there is a significant over-representation of defendants from particular racialised groups; more than half of all these recent prosecutions have concerned heterosexual sex involving a defendant from an African background.
According to the Canadian HIV Legal Network, at least 197 people have been charged for alleged HIV non-disclosure in Canada since 1989. There has been some movement away from prosecutions; Ontario’s attorney-general announced in 2017 that the province would no longer prosecute non-disclosure cases if the suspect has a suppressed viral load. At the same time, a Canadian Federal Department of Justice report argued that Canada should move away from the ‘blunt instrument’ of the law to manage HIV.
Following 2 years of review, Norway’s 2012 Commission on HIV and the Law found that undetectable viral load is not a valid defence to a person with HIV having unprotected sex, whether or not transmission results, although it may be a consideration in sentencing (see Norwegian Commission on HIV and the Law Report (note: the report is in the original Norwegian. An English language summary appears from p 333)).
Resources #
Risk Calculator (An ACON resource that aims to increase gay men’s knowledge about degrees of risk when having sex and takes into account the impact of a low viral load in its ‘risk calculator’)
Muessig K et al., ‘Does ART prevent HIV transmission among MSM?’(2012) AIDS 26 AIDS 2012, 26
P Vernazza et al.,’Les personnes séropositives ne souffrant d’aucune autre MST et suivant un traitment antirétroviral efficace ne transmettent pas le VIH par voie sexuelle’ (2008) 89(5) Bulletin des médecins suisses 165 (English translation, including translator’s affidavit, available here).
HPTN-052 study – MS Cohen et al., ‘Antiretroviral Therapy for the Prevention of HIV-1 Transmission’ (2016) 375(9) The New England Journal of Medicine 375, 830 – 9
Partner Study – AJ Rodger et al., ‘Sexual Activity Without Condoms and Risk of HIV Transmission in Serodifferent Couples When the HIV-Positive Partner Is Using Suppressive Antiretroviral Therapy’ (2016) 316 (2) JAMA 171 Opposites Attract Study – BR Bavinton et al., ‘Viral suppression and HIV transmission in homosexual male serodiscordant couples: an international, prospective, observational, cohort study’ (2018) 5(8) The Lancet HIV E438
