The impact of sexually transmitted diseases (STDs) on the development of cervical intraepithelial neoplasia (CIN) has been increasingly recognized over the last 20 years. Much attention has been focused on human papillomavirus (HPV) and the potential for screening for certain HPV types alongside standard cervical cytology in the hope of identifying those females at particular risk of developing high grade CIN or invasive carcinoma. Some infections, for example herpes simplex virus (HSV), have been heavily investigated in the past as they were thought to be involved in the development of CIN but were subsequently discounted. Also discounted as causes of CIN are Neisseria gonorrhoeae (NG) and Chlamydia trachomatis (CT). These infections were found to be associated with higher rates of CIN in early studies but transpired to be markers for the presence of other infections and pathology and therefore not themselves directly responsible for cytological changes. The role of bacterial vaginosis (BV) is the focus of several current investigations, not only in the genesis of CIN but also in the development of other gynecological and obstetric conditions and complications. Evidence to implicate Trichomonas vaginalis (TV) in the genesis of CIN is conflicting, but there is some evidence that it may exert its influence in a similar way to that hypothesized for BV, ie via abnormal amines.
It is well known that there is a high level of concordance of STDs whereby the presence of one infection greatly increases the likelihood of there being one or more others present. There may be a synergism between some infections with regard to the causation of CIN, although the evidence for this is putative. Presented here is an overview of current and previous research in the field of lower genital tract infection as it relates to the development of CIN.