Is Trichomonas vaginalis a cause of cervical neoplasia? Results from a combined analysis of 24 studies.

BACKGROUND: We conducted this combined analysis of available data from studies with information on this issue to clarify the association between Trichomonas vaginalis infection and cervical neoplasia.
METHODS: We performed MEDLINE searches (1966-1993) using the key words and phrases 'trichomonas vaginitis' and 'neoplasms, cervix' for articles published in English, and searched citations of the articles obtained from MEDLINE: A total of 24 articles (two cohort studies and 22 case-control) were included in this data analysis. In the analysis, the studies were evaluated for heterogeneity using Breslow-Day tests for homogeneity of the odds ratios and of rate ratios. If the odds ratios from studies are heterogeneous, it is not appropriate to combine them using the Mantel-Haenszel method. Also, publication bias was evaluated by assessing the association between the observed effect size and the variance of the effect size using a rank correlation test.
RESULTS: The combined summary relative risk for the two cohort studies was 1.93 (95% confidence interval: 1.22-2.65) indicating an approximate doubling of the risk of cervical neoplasia in the presence of T. vaginalis infection. The attributable risks among exposed subjects and among the source population were 47.4% and 2.1% respectively. Results of the 22 retrospective studies were much less consistent. However, most of them demonstrated a significant positive association.
CONCLUSIONS: This combined analysis suggests that there is an association between T. vaginalis and the risk of cervical neoplasia, but that such infections account for only 2% of cervical neoplasia.