The potential for sexual HIV transmission when a person
living with HIV adheres to antiretroviral therapy and maintains an undetectable
viral load is ‘negligible’, says the Public Health Agency of Canada, in a
review conducted for the country’s Department of Justice. Moreover, the risk of
transmission is ‘low’ when a person living with HIV is taking antiretroviral
therapy without an undetectable viral load of less than 200 copies/ml, condoms
are used, or both.

It is hoped that this confirmation of the scientific
evidence will help curtail the criminalisation of non-disclosure, which is
widespread in Canada. People
can be prosecuted for not disclosing their HIV-positive status when they engage
in sexual activity that poses a “realistic possibility” of HIV transmission.

The Public Health Agency of Canada conducted a systematic
review, in order to identify existing reviews and studies which provided data
to calculate an absolute risk of sexual transmission of HIV between sexual
partners of different HIV statuses.

Studies published up to April 2017 were included. As the
authors acknowledge, this means that some of the most important recent data,
from both the PARTNER
and Opposites
studies, are not included. As no HIV transmissions occurred in
people with undetectable viral loads in these studies, adding their data in
would simply add to our certainty with which we can say that HIV transmission
does not occur in these circumstances.

The review authors looked at various scenarios.

The HIV-positive sex partner is taking
antiretroviral therapy and has a suppressed viral load.
This estimate was based on the older
data from the PARTNER and Opposites Attract studies, in which viral loads below
200 copies/ml were confirmed at least every six months. No HIV transmissions
occurred: 0 transmissions over 1327 person-years (pooled incidence 0.00
transmissions/100 person- years, 95% CI 0.00–0.28). The authors say that if the
more recent data from PARTNER 2 and Opposites Attract were included, the upper
confidence interval of the estimate for would be lowered (from 0.28 to 0.13),
but the point estimate of 0.00 would not change.

The authors
describe the risk of transmission in these circumstances as “negligible”.

The authors
looked for data on condom use in these circumstances, but did not find any
additional studies. If either partner did also use condoms, the risk is also described
as “negligible”.

The HIV-positive sex
partner is taking antiretroviral therapy (with varying levels of viral load).

Some HIV transmissions did occur in the studies which were included: 23 phylogenetically linked HIV
transmissions across 10,511 person-years of follow-up (pooled incidence 0.22
transmissions/100 person-years, 95% CI 0.14–0.33).

The authors
note that people in these cohorts generally had high levels of adherence to treatment
and high levels of viral load suppression. Therefore, the potential for
transmission in these circumstances may have been underestimated.

The HIV-positive sex partner is taking
antiretroviral therapy (with varying levels of viral load) and either partner uses condoms.
There was little evidence to inform this estimate.
The authors rely on a 2012 systematic review which modelled the combined effect
of antiretroviral therapy and condoms to derive per-act risks, ranging from
0.003 transmissions per 1000 acts (95% CI 0.00– 0.03) for insertive vaginal sex
to 0.11 transmissions per 1000 acts (95% CI 0.02–0.73) for receptive anal sex.
This risk is described as “low”.

Either partner uses
condoms, without the
HIV-positive partner taking
antiretroviral therapy.
The authors believe the conclusions of a 2012 Cochrane Collaboration
review still provide the best evidence on this question. This found that among
serodiscordant couples who reported “always” using condoms, there were 1.14 HIV
transmissions per 100 person-years (95% CI 0.56–2.04). The Canadian authors
describe this risk as “low”.

The Canadian Department of Justice used the conclusions of
this study to inform a
report on the justice system’s response to HIV nondisclosure
which was published
a year ago. This stated: “The criminal law should not apply to persons living
with HIV who have engaged in sexual activity without disclosing their status if
they have maintained a suppressed viral load (i.e., under 200 copies per ml of
blood), because the realistic possibility of transmission test is not met in
these circumstances.”

Moreover, “Unprotected sex with an HIV positive person who
has not disclosed their status can no longer be considered to establish a prima
case of HIV non-disclosure as evidence of treatment and viral load
will always be relevant to determining whether the realistic possibility of
transmission test is met.”

However, this important first
step by the federal government towards
limiting unjust HIV criminalisation
does not constitute prosecutorial guidelines, which still need to be
implemented at both the federal and provincial levels.