Prevalence and metronidazole resistance of Trichomonas vaginalis among Japanese women in 2021

Objectives: Trichomonas vaginalis is the most prevalent sexually transmitted parasite worldwide. However, no surveillance system exists to monitor T. vaginalis cases and drug resistance in Japan.

Methods: Cervical cytology vaginal swabs were collected from women with and without suspected symptoms of T. vaginalis infection; these swabs were used for the detection of T. vaginalis, human papillomavirus (HPV), and Candida albicans using specific polymerase chain reaction. Clinical isolates of T. vaginalis were subjected to metronidazole susceptibility tests using the previously reported minimal lethal concentration (MLC) and newly established half-maximal inhibitory concentration (IC₅₀) values.

Results: The prevalence of T. vaginalis in the study population was 4.2% (5/119; 95% confidence interval [Cl], 1.5-9.7). Additionally, asymptomatic infection constituted 60% (3/5) of all cases of T. vaginalis infection. All T. vaginalis-positive patients were coinfected with HPV but not C. albicans. Five clinical T. vaginalis isolates showed metronidazole susceptibility, which was evaluated using MLC values. The quantitative IC₅₀ values revealed that two of these clinical isolates exhibited a decreased metronidazole susceptibility.

Conclusion: This is the first study to demonstrate the prevalence of T. vaginalis in Japanese women. The IC₅₀ values of metronidazole against T. vaginalis enabled the precise and quantitative evaluation of metronidazole-susceptible T. vaginalis.