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

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 infection 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 that of the parC mutation increased from 28.6% to 34.5% (P = 0.66), while the prevalence of 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.