Image: Burnet researcher Michael Traeger presents his study findings at AIDS 2018

New research in partnership with Burnet Institute shows that use of HIV prevention medication, PrEP, is associated with an increase in sexually transmitted infections (STIs).

For those participants who did experience STIs, the study reports that STI risk was influenced more by increased numbers of casual partners and group sex than condom use.

While other studies have linked the use of PrEP to an increase in STIs among gay and bisexual men, the novel methodology of this latest research provides more robust evidence about the change in an individual’s STI rates once they have started PrEP.

The research, presented at the AIDS 2018 conference in Amsterdam, also provides new insights into why some people are more or less likely to acquire STIs on PrEP.

Importantly the study found that over 50 percent of people did not acquire STIs, and that a large number of the STIs occurred in a relatively small proportion of study participants.

Supervising co-author, Associate Professor Edwina Wright, the study’s Principal Investigator said the findings are timely and important because they identify that condom use is not the most important risk factor for STIs in people on PrEP.

“This is a rebuttal to the backlash against PrEP users for reducing condom use,” Associate Professor Wright, an infectious diseases physician and clinical researcher at the Alfred Hospital and Burnet Institute, said.

“The findings also highlight that we might need to target our sexual health messaging about STI risks to a relatively small proportion of PrEP users to help reduce their STI rates.”

The study made use of data collated though ACCESS, The Australian Collaboration for Coordinated Enhanced Sentinel Surveillance of STIs and BBVs, of which Burnet is a member.

This body of routinely extracted clinical data meant that study organisers had ready access to information on STI incidence before the introduction of PrEP.

Study lead author, Burnet research assistant Michael Traeger said very few studies had been able to compare STI incidence before the introduction of PrEP in this way.

“We were able to show in our analysis that starting PrEP was associated with a modest but significant increase in STIs,” said Mr Traeger.

“This knowledge helps shape our understanding of what STI epidemiology will look like in the era of PrEP, and highlights the importance of regular STI screening in the context of wider PrEP scale-up.”

Burnet Head of Public Health and supervising co-author, Professor Mark Stoové said the strength of this research lies in the quality of the program implementation and innovation of the surveillance data systems.

“Being able to identify STI risk down to an individual patient level provides findings that are internationally novel and paints a more informative picture for policy and practice than previous studies have been able to achieve,” Professor Stoové said.

Find out more about Burnet’s HIV research.