Impact of doxycycline post-exposure prophylaxis on the prevalence of resistance-associated mutations of Mycoplasma genitalium among high-risk people

Abstract Objectives Doxycycline post-exposure prophylaxis (DoxyPEP) has been shown to reduce the risk of syphilis and chlamydia among at-risk populations. The impact of DoxyPEP on the trends of Mycoplasma genitalium infection and resistance-associated mutations (RAM) has not been assessed in Taiwan. Methods From September 2021 to September 2025, people with recent sexually transmitted infections (STIs) or at risk of STIs were screened for STIs using a multiplex PCR assay and were consulted for the use of DoxyPEP at a university hospital. All specimens tested positive for M. genitalium were determined for RAMs to macrolides, fluoroquinolones, and tetracycline using an in-house PCR assay. Results During the study period, 325 DoxyPEP users were included. After the implementation of DoxyPEP, the detection rate of M. genitalium among all tests did not change (6.2% vs 5.7%, p=0.64). The overall prevalence of M. genitalium remained stationary (12.0% vs 12.6%, p=0.81). Fifty-six cases of M. genitalium infection were detected during the follow-up and the incidences of M. genitalium infection were similar before and after implementation of DoxyPEP (0.26 vs 0.29 per 1000 person-days; incidence-rate ratio 0.89, 95% CI 0.51-1.57, p=0.68). The prevalence of RAM to tetracycline increased from 10.0% to 24.1% (p=0.28) and the parC mutations increased from 28.6% to 34.5% (p=0.66), while RAM to macrolides decreased from 33.3% to 13.8% (p=0.15). Conclusion After the introduction of DoxyPEP for prevention of syphilis and chlamydia among high-risk populations, the prevalence and incidence of M. genitalium infection remained stable. The increasing trend of RAMs to tetracycline warrants continued surveillance.