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Abstract and Introduction
Abstract
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 μg/mL). Of 538 T. vaginalis isolates, 23 (4.3%) exhibited low-level in vitro metronidazole resistance (minimum lethal concentrations 50–100 μg/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.
Introduction
Trichomoniasis, caused by Trichomonas vaginalis, is one of the most common nonviral sexually transmitted diseases (STDs): annually, ≈248 million incident cases occur worldwide, and ≈7.4 million cases occur in the United States. The estimated US prevalence of T. vaginalis infection is 3.1%, with a higher prevalence among black women and women of low socioeconomic status than among other women. Trichomoniasis is a frequent cause of vaginitis and can contribute to premature rupture of membranes during pregnancy, preterm birth, low birth weight, and may facilitate HIV acquisition.
The Centers for Disease Control and Prevention (CDC) (Atlanta, Georgia, USA) STD Treatment Guidelines recommends the use of a 5-nitroimidazole antimicrobial agent, either metronidazole or tinidazole, for the treatment of T. vaginalis infection. Metronidazole has been the mainstay of treatment for several decades; however, tinidazole has better in vitro activity and is well tolerated.
The reliance on a single drug class for treating T. vaginalis infections may be problematic if resistance to nitroimidazole becomes widespread in T. vaginalis strains. Three small studies that examined the prevalence of in vitro resistance in the United States have been conducted during the past 15 years, but they were limited in geographic scope. Our objective was to assess the prevalence of in vitro aerobic metronidazole and tinidazole resistance among a broad sample of T. vaginalis isolates from multiple geographic sites in the United States.
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