We determined the in vitro minimum lethal concentration (MLC) of secnidazole (SEC) and assessed correlation with clinical susceptibility among T. vaginalis isolates obtained from 71 women, of whom 66 were successfully treated with this medication. An MLC ≤12.5 μg/ml correlated with clinical susceptibility in this study.

BACKGROUND: The only drugs approved by the U.S. Food and Drug Administration for oral treatment of trichomoniasis belong to the 5-nitroimidazole group. Most individuals infected with Trichomonas vaginalis can be cured with a standard treatment of metronidazole or tinidazole, but it is estimated that more than 159,000 people fail treatment each year. Although a minimal lethal concentration (MLC) corresponding to treatment failure has been reported for metronidazole, the MLC for tinidazole associated with treatment failure has not been determined. We conducted a study using T. vaginalis isolates from women with reported treatment success or failure to determine these values. METHODS: We measured MLCs of 47 isolates obtained from women who had failed metronidazole treatment, 33 isolates from women who had failed tinidazole treatment, and 48 isolates from women successfully cured with metronidazole. The cutoff was calculated as the 95th percentile of MLCs of susceptible isolates for each drug. RESULTS: Our data confirmed the MLC previously associated with metronidazole treatment failure is ≥50 μg/ml and identified the MLC associated with tinidazole treatment failure as ≥6.3 μg/ml. For metronidazole, the agreement between laboratory result and treatment outcome was 93.7%, for tinidazole this agreement was 88.9%. CONCLUSIONS: The T. vaginalis susceptibility assay is useful for determining whether 5-nitroimidazole treatment failure in persons with trichomoniasis can be attributed to drug resistance. These results are useful for establishing interpretive guidance of test results and MLC levels can help guide appropriate patient treatment.

BACKGROUND: Trichomonas vaginalis virus (TVV) is a non-segmented, 4.5-5.5 kbp, double-stranded RNA virus infecting T. vaginalis. The objectives of this study were to examine TVV prevalence in U.S. Trichomonas vaginalis isolates and associations with patient demographics, clinical outcomes, and metronidazole resistance. METHODS: Archived T. vaginalis isolates from the enrollment visit of 355 women participating in a T. vaginalis treatment trial in Birmingham, AL were thawed and grown in culture. Total RNA was extracted using Trizol reagent. Contaminating single stranded RNA was precipitated using 4.0M LiCl and centrifugation. Samples were analyzed by gel electrophoresis to visualize a 4.5kbp band representative of TVV. In vitro testing for metronidazole resistance was also performed on 25/47 isolates from the test of cure visit. RESULTS: TVV was detected in 142/355 (40%) isolates at the enrollment visit. Women with TVV+ isolates were significantly older (p = 0.01), more likely to smoke (p = 0.04), and less likely to report a history of gonorrhea (p = 0.04). There was no association between the presence of clinical symptoms or repeat T. vaginalis infection with TVV+ isolates (p = 0.14 and p = 0.44, respectively). Of 25 Test of cure isolates tested for metronidazole resistance, 0/10 TVV+ isolates demonstrated resistance while 2/15 TVV- isolates demonstrated mild-moderate resistance (p = 0.23). CONCLUSIONS: In one of the largest U.S. studies of T. vaginalis isolates tested for TVV, prevalence was 40%. However, there was no association of TVV+ isolates with clinical symptoms, repeat infections, or metronidazole resistance. These results suggest that TVV may be a commensal to T. vaginalis.

BACKGROUND: Among women, trichomoniasis is the most common non-viral sexually transmitted infection worldwide, and is associated with serious reproductive morbidity, poor birth outcomes, and amplified HIV transmission. Single-dose metronidazole is the first-line treatment for trichomoniasis. However, bacterial vaginosis can alter treatment efficacy in HIV-infected women, and single-dose metronidazole treatment might not always clear infection. We compared single-dose metronidazole with a 7-day dose for the treatment of trichomoniasis among HIV-uninfected, non-pregnant women and tested whether efficacy was modified by bacterial vaginosis. METHODS: In this multicentre, open-label, randomised controlled trial, participants were recruited at three sexual health clinics in the USA. We included women positive for Trichomonas vaginalis infection according to clinical screening. Participants were randomly assigned (1:1) to receive either a single dose of 2 g of metronidazole (single-dose group) or 500 mg of metronidazole twice daily for 7 days (7-day-dose group). The randomisation was done by blocks of four or six for each site. Patients and investigators were aware of treatment assignment. The primary outcome was T vaginalis infection by intention to treat, at test-of-cure 4 weeks after completion of treatment. The analysis of the primary outcome per nucleic acid amplification test or culture was also stratified by bacterial vaginosis status. This trial is registered with ClinicalTrials.gov, number NCT01018095, and with the US Food and Drug Administration, number IND118276, and is closed to accrual. FINDINGS: Participants were recruited from Oct 6, 2014, to April 26, 2017. Of the 1028 patients assessed for eligibility, 623 women were randomly assigned to treatment groups (311 women in the single-dose group and 312 women in the 7-day-dose group; intention-to-treat population). Although planned enrolment had been 1664 women, the study was stopped early because of funding limitations. Patients in the 7-day-dose group were less likely to be T vaginalis positive at test-of-cure than those in the single-dose group (34 [11%] of 312 vs 58 [19%] of 311, relative risk 0.55, 95% CI 0.34-0.70; p<0.0001). Bacterial vaginosis status had no significant effect on relative risk (p=0.17). Self-reported adherence was 96% in the 7-day-dose group and 99% in the single-dose group. Side-effects were similar by group; the most common side-effect was nausea (124 [23%]), followed by headache (38 [7%]) and vomiting (19 [4%]). INTERPRETATION: The 7-day-dose metronidazole should be the preferred treatment for trichomoniasis among women. FUNDING: National Institutes of Health.

Metronidazole resistance in the sexually transmitted parasite Trichomonas vaginalis is a problematic public health issue. We have identified single nucleotide polymorphisms (SNPs) in two nitroreductase genes (ntr4Tv and ntr6Tv) associated with resistance. These SNPs were associated with one of two distinct T. vaginalis populations identified by multilocus sequence typing, yet one SNP (ntr6Tv A238T), which results in a premature stop codon, was associated with resistance independent of population structure and may be of diagnostic value.

Nitroimidazoles (metronidazole and tinidazole) are the only recommended drugs for treating Trichomonas vaginalis infection, and previous samples that assessed resistance of such isolates have been limited in geographic scope. We assessed the prevalence of in vitro aerobic metronidazole and tinidazole resistance among T. vaginalis isolates from multiple geographic sites in the United States. Swab specimens were obtained from women who underwent routine pelvic examinations at sexually transmitted disease clinics in 6 US cities. Cultured T. vaginalis isolates were tested for nitroimidazole resistance (aerobic minimum lethal concentration [MLC] >50 microg/mL). Of 538 T. vaginalis isolates, 23 (4.3%) exhibited low-level in vitro metronidazole resistance (minimum lethal concentrations 50-100 microg/mL). No isolates exhibited moderate- to high-level metronidazole resistance or tinidazole resistance. Results highlight the possibility that reliance on a single class of antimicrobial drugs for treating T. vaginalis infections may heighten vulnerability to emergence of resistance. Thus, novel treatment options are needed.

Trichomonas vaginalis is a protozoan parasite that is the cause of the most common non-viral sexually transmitted disease, trichomoniasis. Metronidazole and tinidazole are the only drugs approved for treatment of T. vaginalis infections in the USA. However, drug resistance exists and some patients are allergic to these medications. Furthermore, the exact mechanism of metronidazole resistance remains undefined and current testing methods require several weeks before results are available. Identification of the mechanism of drug resistance may lead to the development of molecular tools to detect drug resistance, and quicker results for clinical treatment. In a recent study, Chinese T. vaginalis isolates that were polymerase chain reaction (PCR) positive for Mycoplasma hominis DNA demonstrated greater in vitro resistance to metronidazole than isolates with no evidence of M. hominis infection. To evaluate this finding in isolates from a distinct epidemiologic setting, we tested 55 T. vaginalis isolates collected from patients in the USA through the Centers for Disease Control and Prevention metronidazole susceptibility testing service. One half of the isolates demonstrated resistance to metronidazole by an in vitro sensitivity assay. Of the metronidazole-resistant T. vaginalis isolates, 18% were PCR positive for M. hominis, as were 22% of the metronidazole-susceptible T. vaginalis isolates (p = 0.746). We also observed no change in metronidazole sensitivity of two infected T. vaginalis isolates after they were cleared of their M. hominis infection by culturing the isolates in antibiotics. Thus, M. hominis infection of USA T. vaginalis isolates did not correlate with in vitro resistance to metronidazole.