In October 2022, San Francisco announced guidelines for doxycycline postexposure prophylaxis (doxyPEP) to prevent bacterial sexually transmitted infections (STIs) in populations at greatest risk. In June 2024, the Centers for Disease Control (CDC) advised specialists to consider doxyPEP with men who have sex with men (MSM) and transgender women with a recent history of STI. The study primarily targets human immunodeficiency virus pre-exposure prophylaxis (HIV PrEP) users and explores doxyPEP use and the rate of STI incidence trends before and after the doxyPEP administration.
This was a retrospective cohort analysis for individuals aged 18 and older who were Kaiser Permanente Northern California (KPNC) members who received HIV PrEP between November 2022 and December 2023. The Institutional Review Board (IRB) accepted the study with an exemption for informed consent since it posed the least risk to the patients and was also carried out to comply with the STROBE declaration.
Data were extracted from electronic health records, including demographics, test results for STIs, and pharmacy records. The primary outcomes included quarterly STI positivity rates for chlamydia, gonorrhea, and syphilis. Secondary outcomes included the occurrence of STIs.
The study also used a primary analysis to investigate differences in STI positivity before and after doxyPEP implementation among recipients, as well as an additional exploratory analysis in a larger group of patients. The initial study comparison of STI positivity rates was done on the patients who were tested for STI 24 months before and 12 months after the start of doxyPEP excluding the initial diagnosis that might influence the results. Poisson regression was used as the model to estimate changes in STI positive and rate ratios (RRs) in the before-and-after study. For statistical analyses, Stata version 17.0 was utilized, and significance was determined using a two-sided P < 0.05 criteria.
The study involved 11,551 participants who initiated HIV PrEP between November 1, 2022, and December 31, 2023, of whom 2253 (19.5%) were given doxycycline post-exposure prophylaxis (doxyPEP). Few significant differences were noted between DoxyPEP and control recipients. DoxyPEP patients were older (mean age 40.4 vs 39.8 years; P = 0.04) and had been in the HIV PrEP program for longer (4.2 vs 3.4 years; P < 0.001). More doxyPEP participants had been treated with a bacterial STI within the 12 months before the start of doxyPEP (48.6% vs. 18.2%, P < 0.001), and a larger percentage had commercial insurance (92.8% vs. 88.9%, P < 0.001).
In chlamydia, the STI incidence positivity reduced from 9.6% before doxyPEP to 2.0% after (RR 0.21, P < 0.001); the reductions at rectal, pharyngeal, and urethral sites were significant (P < 0.001) for all. The STI incidence in gonorrhea was reduced from 10.2% before doxyPEP to 9.0% after the treatment (RR 0.88, P = 0.048). The rate of positivity reduced to 0.3% from 1.7% (RR 0.20, P < 0.001) in syphilis.
This study shows that HIV PrEP users in Northern California experienced fewer STIs when using doxyPEP. After the first year of doxyPEP use, there was a decrease in the STI rates such as chlamydia and syphilis, whereas the decline in gonorrhea was moderate. These outcomes correspond to data obtained in clinical trial studies but highlight the growing concern of antibiotic resistance, specifically in gonorrhea.
The limitations involved where the cohorts had little ethnic diversity (less than 7% of participants were Black), and the study did not include information on individuals’ sexual orientation or gender identity. The diagnoses might have omitted some syphilis cases because they solely relied on laboratory information.
The current study establishes that doxyPEP when co-administered with HIV PrEP reduced the rates of Chlamydia and Syphilis infections and moderately reduced the infections to gonorrhea. Its wider application could be important in achieving the goal of reducing STI spread in the population.
References: Traeger MW, Leyden WA, Volk JE, et al. Doxycycline postexposure prophylaxis and bacterial sexually transmitted infections among individuals using HIV preexposure prophylaxis. JAMA Intern Med. January 6, 2025. doi:10.1001/jamainternmed.2024.7186
