Bacterial STIs Increase Among PrEP Users

Ricki Lewis, PhD

April 10, 2019

Bacterial sexually transmitted infections (STIs) increased in incidence when men who have sex with men (MSM) began using HIV preexposure prophylaxis (PrEP) medications, a study has found. The researchers say frequent testing for STIs may help counter this rise.

"Among gay and bisexual men using PrEP, sexually transmitted infections were highly concentrated among a subset of study participants, and receipt of PrEP after study enrollment was associated with an increased incidence of STIs compared with preenrollment. These findings highlight the importance of frequent STI testing among gay and bisexual men using PrEP," the authors explain.

The study, by Michael W. Traeger, MSc, Disease Elimination Program, Burnet Institute, Melbourne, Victoria, Australia, and colleagues, was published online April 9 in JAMA.

The researchers evaluated data from a subset of 2981 men participating in the Pre-exposure Prophylaxis Expanded (PrEPX) study — a multisite, open-label, population intervention study among MSM who used PrEP and who had at least one follow-up evaluation — to determine the risk for STI and changes in that risk after study enrollment, a "key secondary study objective."

The men were enrolled at five clinics with quarterly HIV and STI testing (for chlamydia, gonorrhea, and syphilis) and clinical monitoring. The investigators also evaluated a subset of 1378 patients for whom data on pre-PrEP STI testing were available.

Of the 2981 participants, 98.5% identified as gay or bisexual males, and 29% used PrEP before enrollment in PrEPX. By the final follow-up, 2892 (97.0%) participants remained in the study.

At a mean follow-up of 1.1 years, 1427 (48%) of the 2981 patients had 2928 STIs (1434 chlamydia, 1242 gonorrhea, and 252 syphilis). Many cases were a result of reinfection; 2237 (76%) of all STIs occurred in 736 (25%) of patients.

Of 2058 participants able to provide details, factors that were associated with greater STI risk were younger age, more anal sex, and more group sex. "[I]n the multivariable analysis, there was no independent association with reported levels of condom use, a factor historically strongly associated with STI risk," the researchers write.

Among the 1378 patients who had undergone at least one STI test before enrollment in the study, STI incidence increased from 69.5 per 100 person-years to 98.4 per 100 person-years at follow-up (incidence rate ratio, 1.41; 95% confidence interval [CI], 1.29 – 1.56). The increase was significant for any of the three STIs. Participants in this subgroup were older and were less likely to have reported injection drug use. They were more likely to have reported using methamphetamines or having more than one episode of insertive condomless sex with a partner whose HIV status was unknown during the 3 months prior to enrollment.

In post hoc analysis, STI incidence during the year before enrollment was significantly greater among patients who were already receiving PrEP (92.4/100 person-years) compared with those who were not receiving it (55.1/100 person-years) (incidence rate ratio, 1.68; 95% CI, 1.47 – 1.91; incidence rate difference, 37.3/100 person-years; 95% CI, 27.7 – 47.0). Among patients who had not used PrEP previously, STI incidence increased significantly to 94.2 per 100 person-years (incidence rate ratio, 1.71; 95% CI, 1.49 – 1.96), mostly for chlamydia.

The researchers conclude that the findings demonstrate the importance of frequent testing for STIs among gay and bisexual men who use PrEP, although they acknowledge the limitation of not including a control group who did not receive PrEP and say the study was not powered to demonstrate that PrEP increases STI risk.

The association of high rates of STIs, including reinfection, among the subgroup who had anal sex and group sex "highlights an opportunity to interrupt community-level STI transmission by offering frequent, easily accessible STI screening and other prevention strategies to PrEP users who are diagnosed with multiple STIs," the investigators write. Efforts should not focus solely on condom use, they add.

In an accompanying editorial, Monica Gandhi, MD, MPH Medicine, University of California, San Francisco, and colleagues refer to the STI and HIV epidemics as a "syndemic." "The tools are now available to end the HIV epidemic, including treatment as prevention and PrEP. Increased PrEP prescribing should lead to more frequent STI screening, which should eventually lead to a reduction in overall STI prevalence," they write.

Clinicians may be underutilizing PrEP, however. "Even though many individuals do not change their condom use behavior after starting PrEP, there is evidence that the concerns of some clinicians about behavioral change may lead them not to offer PrEP to MSM, particularly black MSM, or reserve PrEP for heterosexual serodifferent couples attempting to conceive," Gandhi and colleagues explain.

"It is likely that some individuals with knowledge of the high efficacy of PrEP in preventing HIV infection will change their behavior and that higher-risk behavior is contributing to the current STI epidemic. However, concerns about behavioral change after starting PrEP should not decrease the willingness of clinicians to offer PrEP."

The editorialists also point out that implementing widespread, frequent STI testing may be easier said than done, citing out-of-pocket cost and health insurance plans that will not reimburse rectal and pharyngeal nucleic acid amplification diagnostic testing for STIs. They suggest that the coming inclusion of PrEP in US Preventive Services Task Force recommendations "could help pave the way for improved insurance coverage of STI screening in the United States."

The PrEPX study was supported by funding from the Victorian Department of Health and Human Services, Thorne Harbour Health, and Alfred Health. The researchers and editorialists have disclosed no relevant financial relationships.

JAMA. Published online April 9, 2019. Abstract, Editorial

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