People on PrEP are at risk of acquiring STIs, but it is not because they’re using condoms less new research shows.

Researchers found a 20% increase in the rates of new STIs among people on a PrEP trial in the Australian state of Victoria called PrEPX. PrEP (pre-exposure prophylaxis) is a proven effective HIV preventative medication.

The study included 2,981 mainly gay and bisexual men. Researchers published their results in the Journal of the American Medical Association.

They found there was an increased risk of acquiring an STI while on PrEP compared to before starting PrEP. But they also found there was no link between that increase and the rate of condom use.

Researchers found it ‘surprising’ that ‘condom use was not a significant predictor of acquiring an STI when using PrEP’.

So, why more STIs?

The study found that an increase in casual sex partners and group sex lead to the STI diagnoses. But also like previous studies found that more regular testing explained the increase in STI diagnoses. But results of the study also showed that about 25% of participants accounted for a majority of the diagnoses and that group experienced high rates of STIs.

‘It’s important to understand that when people start taking PrEP, they also get tested more frequently, so STIs are more likely to be detected anyway,’ said lead author, Burnet PhD student Michael Traeger.

He argued the study results should help better guide STI prevention campaigns for people who take PrEP. Those campaigns should not just focus on condom use, but also reducing the time to STI diagnosis through frequent testing.

‘But as PrEP uptake increases, identifying individuals most at risk of STIs will become increasingly important for informing effective and focused STI prevention,’ Traeger said.

End the PrEP backlash

PrEP sceptics often cite the increase risk of STIs while to criticize the medical treatment.

Associate Professor Edwina Wright argued the findings ‘are a rebuttal to the backlash against PrEP users for reducing condom use’.

Wright is the principal investigator of the PrEPX Study, an infectious diseases physician and clinical researcher. She is also the co-head of the HIV Elimination Program at Burnet Institute.

‘The findings are also important because they highlight the need to target our sexual health messaging about STI risks to a relatively small proportion of PrEP users to help reduce their STI rates,’ she said.

‘We need to address these findings by engaging in more research to prevent STIs including STI vaccines and antibiotics that may prevent STIs.’