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One Year of Doxycycline PEP After STI May Prevent 40% of New STIs
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30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle
Mark Mascolini
Using doxycycline postexposure prophylaxis (doxy-PEP) for 12 months after a sexually transmitted infection (STI) diagnosis could prevent about 42% of new STIs, according to an analysis by researchers at Harvard Medical School and Fenway Health in Boston [1]. After an STI diagnosis, doxy-PEP proved similarly effective in people with HIV, preexposure prophylaxis (PrEP) users, and non-PrEP users.
Several studies, including one presented at this CROI meeting [2], confirm lower bacterial STI rates in PrEP users and people with HIV who use doxy-PEP. But concerns remain about antimicrobial resistance with doxy-PEP and about its long-term use, the Harvard/Fenway team observed. They noted that guidelines on doxy-PEP use will have to balance potential benefits and harms. To help guideline writers, the Boston investigators planned this analysis to (1) estimate how many STIs could be averted with different doxy-PEP strategies, and (2) pinpoint strategies that minimize doxy-PEP use while maximizing its impact.
The researchers drew data from (1) Fenway Health, which specializes in LGBTQ+ health and STI care and is the biggest PrEP provider in New England, and (2) electronic health records of gay and bisexual men, transgender women, and nonbinary people assigned male sex at birth who got 2 or more STI tests. This contingent included people with HIV, PrEP users, and non-PrEP users. The investigators started the follow-up clock at the first STI test after January 1, 2015 and stopped the clock at a person's last STI test or December 31, 2020.
The analyses considered 10 strategies: prescribing doxy-PEP to (1) everybody coming in for care, (2) people with HIV and PrEP users, and (3) PrEP users only; and prescribing doxy-PEP for 12 months after an STI diagnosis, including (4) any STI diagnosis, (5) a rectal STI diagnosis, (6) an STI at the current visit plus an STI in the past 12 months, (7) an STI at the current visit plus an STI in the past 6 months, (8) 2 or more concurrent STIs at the same visit, (9) a syphilis diagnosis, and (10) a gonorrhea diagnosis.
Most study group members, 87%, were gay men, 7% bisexual men, 4% trans women, and 2% nonbinary people. More than half of the group, 54%, ever used PrEP, and 14% had HIV infection. Most people in the group, 70.8%, were white, 6.5% black, 6.2% multiracial, 5.9% Asian, and the rest in some other group or without race reported. Hispanics made up 14.6% of the study cohort.
Through 28,324 person-years of follow-up, researchers counted 10,582 STIs for an incidence of 37.4 STIs per 100 person-years (meaning about 37 of 100 people had an STI every year). Incidence per 100 person-years measured 21.6 for chlamydia, 18.6 for gonorrhea, and 5.3 for syphilis.
If everyone in the group were prescribed doxy-PEP, 70% of STIs would be averted. If all people with HIV and PrEP users were prescribed doxy-PEP (68% of all individuals prescribed doxy-PEP), 60% of STIs would be averted. And if all PrEP users were prescribed doxy-PEP (55% of all individuals prescribed doxy-PEP), 49% of STIs would be prevented. If everyone with any STI were prescribed doxy-PEP (41% of all individuals prescribed doxy-PEP), 42% of STIs would be avoided.
A lower number needed to treat (NNT) for 1 year indicates a more efficient strategy. To prevent chlamydia, the most efficient strategies would involve giving doxy-PEP to people with 2 STIs in 12 months (1-year NNT 2.8), giving doxy-PEP to people with 2 STIs in 6 months (1-year NNT 2.5), and giving doxy-PEP to people with 2 or more concurrent STIs (1-year NNT 2.5). To prevent syphilis, the best strategy involved giving doxy-PEP to people with a syphilis diagnosis (1-year NNT 6.0).
Three strategies emerged as the most efficient ways to prevent gonorrhea: giving doxy-PEP to people with 2 STIs in 12 months (1-year NNT 4.1), giving doxy-PEP to people with 2 STIs in 6 months (1-year NNT 3.6), and giving doxy-PEP to people with concurrent STIs (1-year NNT 3.4).
The researchers also found that limiting doxy-PEP to PrEP users and people with HIV did not greatly improve the efficiency (that is, lower the NNT) of any of the 7 strategies listed above.
The Harvard/Fenway investigators outlined three takeaways from their results:
1. "Guidelines should incorporate recent STI diagnosis as an indication for doxy-PEP." For example, the researchers estimated that prescribing doxy-PEP for 12 months after an STI diagnosis could cut the number of STIs by 42%.
2. "Consider people not on PrEP with an STI for doxy-PEP." The research team noted that doxy-PEP has similar efficiency after an STI diagnosis in people with HIV, PrEP users, and non-PrEP users.
3. Local epidemiology should be used to target specific STIs. For example, in their study cohort, prescribing doxy-PrEP after a syphilis diagnosis could prevent 25% of new syphilis cases while using doxy-PEP for only 9% of people.
References
1. Traeger MW, Mayer KH, Krakower DS, Gitin S, Jenness S, Marcus JL. Potential impact and efficiency of doxy-PEP among people with or at risk of HIV. 30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle. Abstract 122.
2. Molina JM, Bercot B, Assoumou A, et al. ANRS 174 DOXYVAC: an open-label randomized trial to prevent STIs in MSM on PrEP. 30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle. Abstract 119.
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