Swiss experts say individuals with undetectable viral load and no STI cannot transmit HIV during sex

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Swiss HIV experts have produced the first-ever consensus statement to say that HIV-positive individuals on effective antiretroviral therapy and without sexually transmitted infections (STIs) are sexually non-infectious. The statement is published in this week’s Bulletin of Swiss Medicine (Bulletin des médecins suisses). The statement also discusses the implications for doctors; for HIV-positive people; for HIV prevention; and the legal system.

The statement, on behalf of the Swiss Federal Commission for HIV / AIDS was authored by four of Switzerland’s foremost HIV experts: Prof Pietro Vernazza, of the Cantonal Hospital in St. Gallen, and President of the Swiss Federal Commission for HIV / AIDS; Prof Bernard Hirschel from Geneva University Hospital; Dr Enos Bernasconi of the Lugano Regional Hospital; and Dr Markus Flepp, president of the Swiss Federal Office of Public Health’s Sub-committee on the clincal and therapeutic aspects of HIV / AIDS.

The statement’s headline statement says that “after review of the medical literature and extensive discussion,” the Swiss Federal Commission for HIV / AIDS resolves that, “An HIV-infected person on antiretroviral therapy with completely suppressed viraemia (“effective ART”) is not sexually infectious, i.e. cannot transmit HIV through sexual contact.”


ribonucleic acid (RNA)

The chemical structure that carries genetic instructions for protein synthesis. Although DNA is the primary genetic material of cells, RNA is the genetic material for some viruses like HIV.



A serodiscordant couple is one in which one partner has HIV and the other has not. Many people dislike this word as it implies disagreement or conflict. Alternative terms include mixed status, magnetic or serodifferent.


The fluid portion of the blood.

prospective study

A type of longitudinal study in which people join the study and information is then collected on them for several weeks, months or years. 


A break in the skin or mucous membrane which involves the loss of the surface tissue.


It goes on to say that this statement is valid as long as:

  • the person adheres to antiretroviral therapy, the effects of which must be evaluated regularly by the treating physician, and
  • the viral load has been suppressed (< 40 copies/ml) for at least six months, and
  • there are no other sexually transmitted infections.

The article begins by stating that the Commission “realises that medical and biologic data available today do not permit proof that HIV-infection during effective antiretroviral therapy is impossible, because the non-occurrence of an improbable event cannot be proven. If no transmission events were observed among 100 couples followed for two years, for instance, there might still be some such events if 10,000 couples are followed for ten years. The situation is analogous to 1986, when the statement ‘HIV cannot be transmitted by kissing’ was publicised. This statement has not been proven, but after 20 years’ experience its accuracy appears highly plausible.”

It then states that the evidence for the Commission’s current assertion about the relationship between treatment and sexual HIV transmisson is much more informed than what was available in 1986 regarding the transmission of HIV through kissing.

For example, they note, Quinn and colleagues found that in sero-discordant couples the risk of transmission depended on the viral load of the HIV-positive partner, and refer also to a prospective study of 393 heterosexual sero-discordant couples from Castilla and colleagues found that there were no infections among partners of persons on antiretroviral therapy, compared to a rate of transmission of 8.6% among partners of untreated patients. They also note that transmission from mother to newborn also depends on the maternal viral load, and can be avoided by taking antiretroviral therapy.

They go on to assert that effective antiretroviral therapy eliminates HIV from genital secretions. They say that HIV RNA, measured in sperm, declines below the limits of detection on antiretroviral therapy, and that HIV RNA is also below the limits of female genital secretions is, as a rule, during effective antiretroviral therapy. “As a rule,” they write, “it rises after, not before, an increase in plasma viral load.”

They also assert that although cell-associated viral genomes are present in genital secretions, even on antiretroviral therapy, these are not infectious virions since “HIV-containing cells in sperm lack markers of viral proliferations such as circular LTR-DNA.”

They note that the concentration of HIV RNA in sperm correlates with the risk of transmission and that “transmission risk declines towards zero with falling sperm viral load. These data indicate that the risk of transmission is greatly decreased by antiretroviral therapy.”

They add, however, several exceptions and caveats to the above statements:

  • After a few days or weeks of discontinuation of antiretroviral therapy, plasma viral load rises rapidly. There is at least one case report of transmission during this rebound.
  • In patients not on treatment, STIs such as urethritis or genital ulcer disease increase the genital viral load; it falls again after the STI is treated.
  • In a patient with urethritis, sperm viral load can rise slightly even while the patient is receiving effective treatment. This rise is small, however, much smaller that the rise observed in patients not on treatment.

They conclude the scientific part of the article by saying that: “During effective antiretroviral therapy, free virus is absent from blood and genital secretions. Epidemiologic and biologic data indicate that during such treatment, there is no relevant risk of transmission. Residual risk can not be scientifically excluded, but is, in the judgment of the Commission, negligibly small.”

Implications for doctors

The Commission then discusses the implications for doctor-patient discussions. It says, "the following information aims to communicate to doctors criteria allowing them to establish whether or not a patient can sexually transmit HIV.

HIV cannot be transmitted sexually if:

  • The HIV-positive individual takes antiretroviral therapy consistently and as prescribed and is regularly followed by his/her doctor.
  • Viral load is ‘undetectable’ and has been so for at least six months
  • The HIV-positive individual does not have any STIs."

Implications for HIV-positive people

The Commission states that an HIV-positive person in a stable relationship with an HIV-negative partner, who follows their antiretroviral treatment consistently and as prescribed and who does not have an STI, is "not putting their partner at risk of transmission by sexual contact."

"Couples must understand," they write, "that adherence will become omnipresent in their relationship when they decide not to use protection, and due to the importance of STIs, rules must be defined for sexual contacts outside of relationship."

"The same goes for people who are not in a stable relationship," they add. However due to the importance of STIs, use of condoms is still recommended.

They add that heterosexual women will have to consider eventual interactions between contraceptives and antiretrovirals before considering stopping using condoms.

They also say that insemination via sperm washing is no longer indicated when "antiretroviral treatment is efficient."

Implications for HIV prevention

The Commission says that it "is not for the time being, considering recommendations that HIV-positive individuals start treatment purely for preventative measures." Aside from the cost involved, they argue, it cannot be certain that HIV-positive people would be sufficiently motivated to follow, and apply to the letter, antiretroviral treatment on a long-term basis without medical indications. They note that poor adherence is likely to facilitate the development of resistance, and that, therefore, antiretroviral therapy as prevention is indicated only in "exceptional circumstances for extremely motivated patients."

The Commission also says that their statement should not change prevention strategies currently taking place in Switzerland. With the exception of stable HIV-positive couples where HIV-positivity and the efficacy of antiretroviral therapy can be established, measures to protect oneself must be followed at all times. "People who are not in a stable relationship must protect themselves," they note, "as they would not be able to verify whether their partner is positive or on efficient antiretroviral therapy."

Implications for the legal system

Finally, the Commission says that courts will have to take into account the fact that HIV-positive people on antiretroviral treatment and without an STI cannot transmit HIV sexually in criminal HIV exposure and transmission cases.

They conclude by stating that the Commission thinks that unprotected sex between a positive person on antiretroviral treatment and without an STI, and an HIV-negative person, does not comply with the criteria for an “attempt at propagation of a dangerous disease” according to section 231 of the Swiss penal code nor for “an attempt to engender grievous bodily harm” according to section122, 123 or 125.