31. WHY HAS TRICHOMONAS VAGINALIS DECLINED DRAMATICALLY AMONG VICTORIAN WOMEN (1947-2005)?

Abstract

Trichomonas vaginalis (TV) diagnosis rates have decreased considerably in some countries during the last two decades. It is unclear why TV has decreased only in some countries. This study investigated the relationships between: 1) TV diagnosis rates among women attending the Melbourne Sexual Health Centre (MSHC), and among Pap smears screened by Victorian Cytology Services (VCS); 2) the use of nitroimidazoles in Australia and; 3) gonorrhoea notification data for Victoria to assess changes in sexual behaviour.

TV diagnosis rates among women attending MSHC rose from under 5% in the 1940's, to 20% to 30% in the 1960's and then declined 5% to 10% during the 1970's. From 1980 onwards, TV diagnosis rates fell progressively to below 1% by 1991, with 0.1% in 2004. A similar pattern was seen in TV at VCS, but with lower absolute percentages. Metronidazole was introduced into Australia in 1961 and tinidazole in 1976 and by 1987 there were 400 000 nitroimidazole prescriptions per year. Pap smear screening in Victoria began in 1965, only including 20% of women per year (aged 15 to 69) by the mid 1980's. Post 1980's, screening rose until 2000, stabilising at 35% of women per year. Gonorrhoea notification rates peaked during times TV was experiencing its greatest falls.

The initial decline of TV seen in Victoria was associated with the introduction of effective antibiotics. The further decline to less than 1% was seen when Pap smear screening participation increased during the 1990's.