UK conference discusses the `Swiss statement` on infectiousness of people on HIV treatment

This article is more than 12 years old. Click here for more recent articles on this topic

There was broad consensus at last week’s autumn conference of the British HIV Association that effective HIV treatment significantly reduces the risk of HIV transmission. But nobody – even a leading proponent of what has become known as the `Swiss statement` – was prepared to say that HIV transmissions never occurred when an individual had an undetectable viral load.

In January this year leading Swiss HIV doctors issued a statement saying that HIV-positive individuals who were taking antiretroviral therapy with an undetectable viral load in their blood and no sexually transmitted infections could not pass on HIV to their sex partner. It quickly became known as the `Swiss statement` and has been hotly debated ever since, becoming one of the top subjects of this year’s International AIDS Conference in Mexico City.

A consensus quickly emerged that HIV treatment that suppresses viral load in the blood to undetectable levels does significantly reduce the risk of HIV transmission during unprotected sex. A dissenting voice, however, was raised by some Australian HIV doctors who developed a model that assumed that there was no lower limit below which HIV transmission could not occur. But an editorial which accompanied this paper rejected this methodology, the authors writing that denying the impact of HIV treatment on transmission risk was “dishonest and futile”.


Swiss statement

A 2008 article by a group of Swiss doctors which asserted that people living with HIV who are taking antiretroviral therapy and have an undetectable viral load, with no sexually transmitted infections, do not pass on HIV to their sex partners. Since then, major scientific studies have proven that the statement was correct.

safer sex

Sex in which the risk of HIV and STI transmission is reduced or is minimal. Describing this as ‘safer’ rather than ‘safe’ sex reflects the fact that some safer sex practices do not completely eliminate transmission risks. In the past, ‘safer sex’ primarily referred to the use of condoms during penetrative sex, as well as being sexual in non-penetrative ways. Modern definitions should also include the use of PrEP and the HIV-positive partner having an undetectable viral load. However, some people do continue to use the term as a synonym for condom use.


The process of viral multiplication or reproduction. Viruses cannot replicate without the machinery and metabolism of cells (human cells, in the case of HIV), which is why viruses infect cells.

detectable viral load

When viral load is detectable, this indicates that HIV is replicating in the body. If the person is taking HIV treatment but their viral load is detectable, the treatment is not working properly. There may still be a risk of HIV transmission to sexual partners.

voluntary male medical circumcision (VMMC)

The surgical removal of the foreskin of the penis (the retractable fold of tissue that covers the head of the penis) to reduce the risk of HIV infection in men.

The autumn meeting of the British HIV Association provided an opportunity for UK doctors, healthcare workers and community activists to discuss the science behind the `Swiss statement` and its impact on people living with the virus.

'Undetectable = uninfectious'

No new scientific information that has not already been extensively discussed in relation to the debate about 'undetectable = uninfectious' was presented. Prof. Bernard Hirschel of Geneva University Hospital briefly discussed the studies showing that patients with an undetectable viral load were not transmitting HIV.

He also presented a slide summarising a study conducted in Rwanda that showed that HIV treatment was much more effective at preventing HIV transmission than promotion of condoms. This study, presented to the International AIDS Conference in 2006 (Kayitenkore K et al. 14th International AIDS Conference Toronto 2006, abstract no. MOKC101), showed that there were only 2 HIV transmissions in 248 serodiscordant couples where the HIV-positive partner was receiving HIV therapy (a transmission rate below 1%) compared to 40 transmissions (a transmission rate above 5%) in serodiscordant couples where the HIV-positive partner did not receive HIV treatment and who had condoms promoted to them. He therefore told the conference that data appeared to show that effective HIV treatment was more efficacious than condoms at preventing HIV transmission.

In support of the 'undetectable = uninfectious' argument, Prof. Hirschel also summarised studies showing the reduction in the risk of mother-to-child HIV transmission when a mother is taking HIV treatment and has an undetectable or very low viral load.

Nevertheless Prof. Hirschel conceded that in medicine you should “never say never” and also that the information to date was restricted to heterosexual couples.

HIV replication in sexual compartments

Dr Steve Taylor of the University of Birmingham presented information from a number of studies that have looked at HIV replication in the genital tracts of men and women who are taking HIV treatment.

A consistent pattern emerged in these studies. Men with an undetectable viral load almost always had undetectable HIV in their semen (although viral load could become detectable in semen if a sexually transmitted infection was present).

In women, however, studies have revealed a more complex picture with up to 30% of women continuing to shed HIV in their genitals despite having an undetectable viral load in their blood.

Dr Taylor suggested that localised HIV replication in the genital compartment during HIV therapy may in some circumstances lead to the development and potential transmission of drug resistant virus.

Dr Taylor also noted that there was very limited information on the effect of HIV treatment on viral load in the rectal mucosa. The one study that has explored this found that HIV was still detectable in this compartment in the presence of effective HIV treatment.

The community response – gay men

Edwin Bernard, editor of NAM’s HIV Treatment Update (which has published three major articles in recent years looking at the impact of treatment on infectiousness) outlined community response (largely from gay men) to the `Swiss statement`.

He likened this response to the classic “grieving process” with individuals seeking to deny the Statement, reacting with anger, bargaining, becoming depressed about its implications, or accepting it.

He noted that for gay men, the statement resonates more strongly for men who have a problematic relationship with condoms, primarily because they perceive that sex without condoms provides greater intimacy.

He also said that an individual's relationship to risk and risk perception was also critical in their interpretation of the Statement. If successful treatment changes the definition of 'safer sex', then deciding how safe 'safer sex' actually is becomes a very personal, individualised decision.

Clinicians, as well as people with HIV and their sexual partners, require better skills to understand and assess the risks of sex compared with other risks in life, he concluded.

The community response – women

Silvia Petretti of Positively Women presented the results of consultation conducted with HIV-positive women about the Swiss statement. This revealed a range of responses with women seeing both pros and cons.

The perceived cons included a muddying of safer sex messages, and some women also noted that it could make negotiating safer sex harder. Concerns were also raised about the implications of chronic genital herpes. It was also suggested that the Statement could mean that sexual health is perceived only in terms of HIV transmission risk and there were questions about its implications for injecting drug users.

But the women consulted by Silvia Petretti also saw benefits in the `Swiss statement`. Some women said that the statement supported what they were already doing, and it was also suggested that an implication could be that it made conception easier. Other benefits included an incentive to maintain good adherence.

Stigma could also be reduced by the statement if people with HIV on treatment were no longer perceived as “vectors” of disease.

She noted, however, that many of the women consulted were unaware of the statement and contrasted this with the widespread knowledge about the studies suggesting that circumcision could reduce men’s risk of HIV. Of note, the protective effective of circumcision in these studies is at most 60%, much lower than the protective effective of treatment.

Wider UK responses

Only an hour was made available by the conference organisers for this session and there was little time for detailed discussion of the presentations or questions from the floor.

However, Prof. Hirschel noted that the small number of infections likely to occur from individuals with an undetectable viral load were of negligible public health significance compared to the large number of infections originating in undiagnosed individuals, a comment that was greeted with applause.