An emerging trend in STI Management: Antibiotic STI Post-Exposure Prophylaxis Prevalence and Determinants in Recent Surveys

This study synthesizes data from nine English surveys (2019–2024) to reveal that antibiotic STI post-exposure prophylaxis use among GBMSM increased from 3.61% to 13.05% over time, with higher prevalence significantly associated with specific demographics (such as transgender women, Black and Asian individuals, and people living with HIV) and high-risk behaviors like chemsex and condomless sex, while noting limitations in generalizability to underrepresented groups.

The Gist

Imagine the UK's sexual health landscape as a massive, bustling city. In this city, there's a growing problem with a specific type of infection called syphilis, which has been hitting record highs. To fight this, health officials are considering a new strategy: giving people a "preventive shield" (antibiotics) after they've had risky sex but before they get sick. This is called STI Post-Exposure Prophylaxis (PEP).

This paper is like a giant detective report that looks at nine different snapshots of the city taken between 2019 and 2024 to answer two main questions:

1. How many people are already using this shield?
2. Who are these people, and what are they doing?

Here is the breakdown of what the researchers found, using simple analogies:

1. The "Early Adopters" are Growing

Think of STI PEP use as a new app that people are starting to download.

• The Trend: In 2020, only about 3.6% of the people surveyed had the app installed. By 2024, that number jumped to 13%.
• The Meaning: A significant minority of gay, bisexual, and other men who have sex with men (GBMSM) in England are already taking antibiotics after sex to prevent infections, even before the government officially recommended it as a standard rule.

2. Who is Using the Shield? (The Demographics)

The researchers built a "profile" of the typical user. It's not a random mix of everyone; it's a specific crowd.

• The Age Group: The "sweet spot" for users is people in their early 40s.
  • Analogy: Think of it like a gym membership. The 20-somethings are just starting to think about it, the 60-somethings are mostly retired from the scene, but the 40-somethings are the most active members.
• The Gender: Transgender women are much more likely to use this shield than cisgender men.
• The Ethnicity: Surprisingly, Black and Asian individuals were more likely to use it than White individuals. This was unexpected because, in the past, these groups often had lower uptake of other health tools (like HIV PrEP).
• The HIV Factor: People living with HIV are significantly more likely to use STI PEP. It's like they are already wearing a heavy-duty raincoat (HIV treatment) and are now adding an umbrella (STI PEP) for extra protection.

3. The "Risk Radar" (Behavioral Factors)

The study found that people who use this shield are the ones who are already playing with fire.

• Chemsex: People who use drugs during sex are twice as likely to use STI PEP.
• No Condoms: People who have sex without condoms are more likely to use it.
• Recent Infections: If you've been diagnosed with an STI recently, you are much more likely to start using the shield.
• The Metaphor: Imagine a group of people who love driving fast cars without seatbelts. These are the same people who are most likely to buy a high-tech airbag system after they've already been in a few near-misses. The people taking the medicine are the ones who know they are at the highest risk.

4. The "Time Machine" Effect

The study noticed a massive spike in usage in 2024.

• Why? The researchers suggest this is like a viral marketing campaign. Public awareness grew, perhaps because the US released new guidelines about this treatment, making more people in the UK aware that it exists.

5. The "Blind Spots" (Limitations)

The paper is very honest about what it doesn't know.

• The Sample Bias: The surveys mostly caught people who are already very engaged with sexual health services. It's like trying to understand the whole city's driving habits by only interviewing people at a car repair shop.
• Missing Groups: The study didn't capture enough women, heterosexual people, or very young people. So, while we know a lot about the "high-risk GBMSM" crowd, we don't have a clear picture of how widespread this is in the general population.

The Bottom Line

This paper acts as a baseline snapshot. It tells us that before the UK officially rolled out a national recommendation for this antibiotic treatment, a specific group of high-risk men were already using it.

The researchers conclude that because the people using it are the ones taking the biggest risks, the new official rules might naturally find a home with the people who need it most. However, they warn that we need better data to make sure we aren't missing the people who are suffering in silence but aren't part of these specific surveys.

Technical Summary

Technical Summary: Antibiotic STI Post-Exposure Prophylaxis Prevalence and Determinants in Recent Surveys

Problem Statement
The study addresses the emerging trend of antibiotic post-exposure prophylaxis (STI PEP) use among gay, bisexual, and other men who have sex with men (GBMSM) in England. While doxycycline PEP (doxyPEP) has been investigated for efficacy against syphilis and other bacterial STIs, and recommended in the US and UK for high-risk groups, there is a lack of comprehensive data regarding its prevalence and the demographic or behavioral characteristics of "early adopters" prior to formal widespread implementation. Understanding the baseline characteristics of current users is critical for evaluating the future impact of official recommendations and monitoring potential disparities in uptake.

Methodology
The authors conducted a secondary analysis synthesizing individual-level data from nine distinct surveys conducted in England between 2019 and 2024. The datasets included the Gay Men's Sexual Health Survey (GMSHS), PrEP Users Surveys, the Prevalence of Prophylaxis for STIs (POPS) survey, and four waves of the Reducing Inequalities in Sexual Health (RiiSH) survey.

• Data Harmonization: To address variations in survey questions and lookback periods (ranging from three months to "ever"), the authors generated composite binary indicators for STI diagnosis, chemsex use (specifically GHB/GBL, methamphetamine, or methadone), and history of condomless anal sex.
• Statistical Approach: The primary outcome was self-reported STI PEP use. The analysis employed mixed-effects logistic regression to assess associations between STI PEP use and various predictors.
  • Missing Data: Multiple imputation (chained logistic regression) was used to handle partial missingness in covariates (education, HIV status, PrEP history, STI diagnosis). Participants missing core sociodemographic data were excluded.
  • Model Structure: The model included fixed effects for survey year, age, gender, ethnicity, HIV status, sexual orientation, and behavioral factors. To account for heterogeneity in variable definitions across surveys, composite variables were tested for interaction with the survey. STI diagnosis was included as a random effect due to significant interaction effects; a random intercept was included for each survey to account for baseline prevalence differences.
• Software: Analyses were performed using STATA 18.0.

Key Contributions

• Synthesis of Longitudinal Data: This is the first study to pool data from nine surveys over a five-year period (2019–2024) to estimate STI PEP prevalence in England, providing a more robust sample size (N=14,142) than previous single-survey analyses.
• Granular Characterization: The study provides a detailed profile of early adopters, moving beyond simple prevalence estimates to identify specific demographic and behavioral determinants.
• Baseline Establishment: The analysis establishes a pre-recommendation baseline for STI PEP use, which is essential for future evaluation of the impact of the UK's doxyPEP guidelines.

Results

• Prevalence Trends: STI PEP use prevalence varied significantly across surveys, ranging from 3.61% (95% CI: 2.78–4.68%) in RiiSH 2020 to 13.05% (95% CI: 11.85–14.36%) in RiiSH 2024.
• Demographic Determinants:
  • Age: Use was significantly higher in the 40–44 age group (aOR = 1.26) compared to the 30–34 reference group, and lower in those under 25 (aOR = 0.56) and over 65 (aOR = 0.64).
  • Gender: Transgender women had substantially higher odds of use compared to cisgender men (aOR = 3.87).
  • Ethnicity: Black (aOR = 1.85) and Asian (aOR = 1.43) individuals had higher odds of use compared to White individuals.
  • HIV Status: People living with HIV were significantly more likely to use STI PEP (aOR = 3.40) compared to those with a recent negative test.
• Behavioral Determinants:
  • Chemsex: Engagement in chemsex was strongly associated with use (aOR = 2.15).
  • Condomless Sex: History of condomless anal sex was associated with increased odds (aOR = 1.59).
  • STI History: A recent STI diagnosis was associated with higher odds of use (aOR = 1.83).
• Temporal Trends: There was a substantial increase in the odds of STI PEP use in 2024 compared to 2019 (aOR = 4.67), suggesting a rapid rise in adoption in the most recent period.

Significance and Claims
The paper claims that STI PEP use is already established among a significant minority of GBMSM in the UK, particularly among those engaging in behaviors associated with higher STI risk (chemsex, condomless sex, recent STI diagnosis) and specific demographic groups (transgender women, people living with HIV, and certain ethnic minorities).

The authors assert that these findings provide a necessary baseline to estimate the impact of the formal recommendation of doxycycline for STI PEP in the UK. They note that while the results suggest high uptake may occur in high-risk groups where the intervention could be most effective, the study is limited by participation and sampling biases. Specifically, the sample underrepresents women, heterosexuals, and certain ethnic minorities, limiting the generalizability of the findings to the broader population. Consequently, the authors conclude that while this analysis offers the most granular characterization of STI PEP users to date, future surveys must include more comprehensive samples to fully understand potential inequities in implementation.