HIV treatment as prevention: the Ugandan experience

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Antiretroviral therapy (ART) is associated with a substantial and sustained reduction in the risk of sexual transmission of HIV, according to results of an observational study published in AIDS. The research involved people living in rural Uganda. Data were collected on viral suppression with ART and sexual risk behaviour. Overall, virologically suppressive ART reduced the risk of sexual transmission of HIV by 90%.

“Our findings corroborate prior work describing the enormous potential of ART to prevent transmission in HIV-endemic, resource-limited settings,” comment the authors.

A growing body of data shows that virologically suppressive antiretroviral therapy (treatment which reduces viral load to an undetectable level) is associated with a near-zero risk of sexual transmission of HIV.


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.

observational study

A study design in which patients receive routine clinical care and researchers record the outcome. Observational studies can provide useful information but are considered less reliable than experimental studies such as randomised controlled trials. Some examples of observational studies are cohort studies and case-control studies.

risky behaviour

In HIV, refers to any behaviour or action that increases an individual’s probability of acquiring or transmitting HIV, such as having unprotected sex, having multiple partners or sharing drug injection equipment.


The presence of virus in the blood.


virological suppression

Halting of the function or replication of a virus. In HIV, optimal viral suppression is measured as the reduction of viral load (HIV RNA) to undetectable levels and is the goal of antiretroviral therapy.

This means that people taking antiretroviral therapy can, in theory, only transmit HIV to sexual partners if their viral load is detectable – above 400 copies/ml. 

But it is unclear how often people taking ART have sexual encounters that involve such a risk of HIV transmission.

An international team of investigators therefore designed an observational study involving 463 adults living with HIV in rural Uganda who were starting ART.

“Our goal was to measure the potential impact and durability of ART to mitigate transmission risk for PLWHA [people living with HIV/AIDS] on long-term treatment in an HIV-endemic, resource-limited setting,” explain the authors.

Every three months, the study participants had their viral load monitored and answered questions about their recent sexual behaviour, including the HIV status of their partners and condom use.

Each 90-day period was considered to involve a risk of HIV transmission if a participant had a detectable viral load and reported unprotected sex with a partner who was HIV negative or whose HIV status was unknown.  

Most (70%) of the participants were women and their median age was 34 years. Median CD4 count and viral load at baseline were 136 cells/mm3 and 126,000 copies/ml, respectively. The participants were followed-up in the study for a median of 3.5 years, and during this time contributed a total of 5923 study visits.

During follow-up, 59% of participants had either detectable viral load or reported sexual behaviour involving a risk of HIV transmission at least once. However, only 5% of participants had simultaneous viraemia and transmission risk behaviour, and this occurred at less than 0.5% of study visits.

“ART provided a sustained, more than 90% reduction in periods of HIV transmission risk by imparting undetectable viral loads to individuals when risky sexual behaviour was reported,” write the authors.

Several characteristics were associated with the reporting of risky sexual behaviour while having a detectable viral load. These included younger age (p = 0.01), higher HIV-related internalised stigma score (p = 0.04) and lower CD4 count (p = 0.01).

“ART reduced periods of potential HIV transmission risk by over 90% in a population of PLWHA in Uganda during up to 6 years of observation time,” conclude the authors. “These findings provide further support for the provision of ART to all PLWHA meeting guidelines to reduce HIV transmission in HIV-endemic settings.”


Siedner MJ et al. Treatment as long-term prevention: sustained reduction in HIV sexual transmission risk with antiretroviral therapy in rural Uganda. AIDS 28; 267-71, 2014.