Metronidazole-Resistant Vaginal Trichomoniasis — An Emerging Problem

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Abstract
Trichomonal resistance to metronidazole was reported soon after its introduction and has been reported in many areas in the world. Although a sexually transmitted disease with dire consequences related to human immunodeficiency virus transmission, trichomoniasis is not a reportable infection, and epidemiologic data on its incidence in the United States are not available. Therefore, it is not surprising that accurate figures on metronidazole-resistant trichomoniasis are almost nonexistent. Nevertheless, clinically important resistance is considered rare, with estimates of high-level resistance to metronidazole occurring in only 1 in 2000 to 3000 cases.1 In clinics specializing in chronic vaginitis that were established in Detroit and Philadelphia in 1985 and 1991, respectively, we consistently observed no more than one case of metronidazole-resistant vaginal trichomoniasis annually before 1996 ( Figure 1 ). In contrast, during 1997 and 1998, we diagnosed 17 cases, a dramatic increase in referred cases despite a relatively constant number of patients seen. Although some accrual bias is possible, this large increase is remarkable and deserves attention. Clinical resistance was defined as failure to respond to conventional therapy with oral metronidazole, either 2 g as a single dose or 500 mg twice daily for five to seven days, excluding cases with probable reinfection. Failure to respond was defined as persistence or recurrence of symptoms and signs of vaginitis together with the confirmatory laboratory features of vaginal trichomoniasis, such as high vaginal pH, increased numbers of polymorphonuclear leukocytes, and visualization of motile trichomonads on microscopy.

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