Doxycycline post-exposure prophylaxis (doxy-PEP) reduces bacterial sexually transmitted infection (STI) risk in people with HIV (PWH) or using HIV preexposure prophylaxis (PrEP). However, ongoing decision-making about federal and local guidance for doxy-PEP prescribing is complicated by concerns about potential harms of widespread use. We sought to identify doxy-PEP prescribing strategies that would minimize overall doxy-PEP use while maximizing impact on STIs.
We used electronic health record data on gay and bisexual men (GBM), transgender women, and non-binary people assigned male at birth with ≥2 STI tests (chlamydia, gonorrhea, or syphilis) at Fenway Health, a Boston clinic focused on LGBT health, during 2015-2020. Patients were followed from first STI test until last test or end of 2020. We defined 10 potential doxy-PEP prescribing strategies: prescribed to (1) all individuals, (2) PrEP users, (3) PrEP users/PWH; and prescribed after (4) any STI, (5) rectal STI, (6) ≥2 STIs in 12m, (7) ≥2 STIs in 6m, (8) ≥2 concurrent STIs, (9) syphilis or (10) gonorrhea Dx. We also explored strategies 4–10 restricted to PrEP users/PWH. We evaluated counterfactual scenarios in which patients who met each criterion were prescribed doxy-PEP indefinitely (strategies 1–3) or for 12m (strategies 4–10). We assumed STI incidence during doxy-PEP use would have been reduced by clinical trial efficacy estimates. For each strategy, we estimated the proportion prescribed doxy-PEP, overall STIs averted, and number needed to treat with doxy-PEP per year to avert 1 STI (NNT).
Among 10,562 patients (94% GBM; 54% PrEP users; 14% PWH), incidence of any STI was 39.8/100py. Across strategies, NNT ranged from 1.0–3.8 (median=1.7) and proportion of STIs averted ranged from 8%–70% (median=20%). Prescribing doxy-PEP to all patients averted 70% of STIs (NNT=3.7); prescribing to PrEP users/PWH (68% of patients) averted 60% of STIs (NNT=2.9; Figure). Prescribing doxy-PEP after any STI reduced the proportion of patients on doxy-PEP to 41% and averted 42% of STIs (NNT=2.9). Prescribing after concurrent or repeated STIs was most efficient (lowest NNTs). Restricting strategies 4–10 to PrEP users/PWH had minimal effect on NNT and reduced impact on STIs.
Prescribing doxy-PEP to individuals with STIs, particularly concurrent or repeated STIs, could avert a substantial proportion of subsequent STIs. The most efficient prescribing strategies are based on STI history rather than HIV status or PrEP use.
Proportion of individuals prescribed doxy-PEP (red), proportion of STIs averted (blue), and number needed to treat (NNT) with doxy-PEP for one year to avert one STI (right) for each doxy-PEP prescribing strategy.