April 09, 2019
3 min read

PrEP associated with increase in STIs among gay, bisexual men

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Michael W. Traeger MSc
Michael W. Traeger

The use of pre-exposure prophylaxis, or PrEP, for HIV prevention was associated with an increase in the incidence of STIs among gay and bisexual men during a multi-year study conducted in Australia, according to findings published today in JAMA.

STI diagnoses were “highly concentrated” among those who were of a younger age, had a high number of sexual partners and participated in group sex, but were not independently associated with reported condom use, “a factor historically strongly associated with STI risk,” researchers wrote.

“The incidence of bacterial STIs increased among this cohort of gay and bisexual men after receipt of PrEP, however, the testing rate for STIs also increased significantly as a result of regular clinic visits for PrEP, which involved routine STI screening,” Michael W. Traeger, MSc, a research assistant at the Burnet Institute in Melbourne, Australia, told Infectious Disease News.

According to the CDC, daily use of PrEP use can reduce the risk for HIV by more than 90%. In a study published last year, researchers reported a 1-year decline of 25% in new HIV diagnoses among men who have sex with men as a result of a rapid, targeted roll out of PrEP in New South Wales, Australia.

PrEP pill 
PrEP for HIV prevention is associated with an increase in the incidence of STIs, researchers found.
Source: Adobe Stock

But worries remain. In an editorial related to the JAMA study, experts highlighted the concern that PrEP use may lead to changes in sexual behavior, “such as decreased condom use and a greater number of partners.”

“These changes in sexual behavior could exacerbate the STI epidemic,” wrote Monica Gandhi, MD, MPH, and Matthew A. Spinelli, MD, of the University of California, San Francisco, and Kenneth H. Mayer, MD, of The Fenway Institute.

Traeger and colleagues conducted a multisite, open-label intervention study called the Pre-exposure Prophylaxis Expanded Study, or PrEPX, to investigate changes in STI incidence and behavioral risk factors among gay and bisexual men who use PrEP in Australia.

Between July 26, 2016, and April 1, 2018, they enrolled 4,275 participants, including 2,981 who enrolled at a clinic in the Australian Collaboration for Coordinated Enhanced Sentinel Surveillance network and who had at least one follow-up visit. Participants received daily oral tenofovir disoproxil fumarate and emtricitabine for HIV PrEP upon enrollment and had quarterly HIV and STI testing, as well as clinical monitoring.

According to the study, 98.5% of participants identified as gay or bisexual, 29% used PrEP before enrollment in the study and the median age of participants was 34 years. Eighty-nine individuals withdrew from the study.


The mean follow-up was 1.1 years, during which 2,928 STIs were diagnosed among 48% of participants. Specifically, 1,434 participants contracted chlamydia, 1,242 contracted gonorrhea and 252 contracted syphilis, according to Traeger and colleagues. A quarter of participants accounted for 76% of diagnosed STIs during the study period, and the overall STI incidence was 91.9 per 100 person-years, the researchers reported.

“As condom use was not significantly associated with STI risk, findings suggest that the increase in STI incidence following the receipt of PrEP may be associated with more complex factors, such as changes in sexual networks or other unmeasured sexual behaviors,” Traeger said.

When they compared STI incidence pre-enrollment and post-enrollment, Traeger and colleagues observed that it increased from 69.5 STIs per 100 person-years before study enrollment to 98.4 per 100 person-years during study follow-up (incidence rate ratio [IRR] = 1.41; 95% CI, 1.29-1.56).

Adjusting for the frequency of testing revealed a significant increase in the incidence of any STIs (adjusted IRR = 1.12; 95% CI, 1.02-1.23) and chlamydia (aIRR = 1.17; 95% CI, 1.04-1.33) from 1 year pre-enrollment to follow-up.

“Ongoing monitoring of STI incidence and STI screening rates among PrEP users with be critical in curtailing rising STI rates. Our study warrants further research into novel ways to prevent STIs, such as STI vaccines or antibiotics for prevention,” Traeger said.

In the editorial, Gandhi and colleagues said it is possible to end the HIV epidemic with currently available tools, namely through treatment as prevention and PrEP. Although they said that the results of the PrEPX study “should not be interpreted in isolation,” Gandhi and colleagues noted that increased use of PrEP should lead to increased STI testing.

“The HIV and STI epidemics comprise a syndemic that is now addressable,” Gandhi and colleagues wrote. “The onus is now on health care systems and clinicians to promote and implement the comprehensive sexual health services that are needed to achieve the elimination of HIV transmissions and the end of the current STI epidemic.” – by Marley Ghizzone

Disclosures: Gandhi, Spinelli and Traeger report no relevant financial disclosures. Mayer reports receiving an unrestricted research grant from Gilead Sciences. Please see the study for all other authors’ relevant financial disclosures.