Temporal associations with declining Trichomonas vaginalis diagnosis rates among women in the state of Victoria, Australia, 1947 to 2005

Background: To investigate the temporal associations between Trichomonas vaginalis (TV) diagnoses in women at a large urban sexual health clinic and a major Papanicolaou (Pap) smear screening laboratory in Victoria, Australia with Pap smear screening rates and the introduction of nitroimidazole treatments. Methods: An ecological analysis of TV diagnosis rates at the Melbourne Sexual Health Centre and the Victorian Cytology Service, Pap smear screening rates and nitroimidazole prescription data. Results: Diagnoses of TV at the Melbourne Sexual Health Centre peaked in the 1950s at 20% to 30% and then rapidly declined through the 1960s and 1970s to below 1% in 1990. A similar pattern was observed at the Victorian Cytology Service. Metronidazole prescribing and opportunistic Pap smear screening began in Victoria in the 1960s coinciding with declining TV. The availability of tinidazole in 1976 led to further declines in TV in the late 1970s. A national cervical screening program introduced in 1991 was temporally associated with further declines in TV. Conclusions: Our analyses suggest that the introduction of metronidazole was associated with a large reduction in TV among Victorian women in the 1960s. The subsequent availability of tinidazole and increased Pap smear screening may have contributed to the current low TV prevalence in Victoria.