Molecular epidemiology and genotyping of Chlamydia trachomatis infection in a cohort of young asymptomatic sexually active women (18-25 years) in Milan, Italy

Abstract

Introduction: Chlamydia trachomatis (Ct) is the most common bacterial cause of sexually transmitted infections (STI) and is associated with severe long-term sequelae in female populations. In Italy Ct infections are not submitted to a screening programme, and its epidemiological profile is understudied. Even scarcer information is available about the genetic diversity on ompA gene, whose sequence defines 18 different genovars. This study aims at evaluating the prevalence of Ct infection in young sexually active asymptomatic women aged 18-25, and characterizing the molecular epidemiology of the different circulating genovars in this population.

Methods: Cervical samples collected from 909 sexually-activeyoung women (mean age 21.5 years) were analyzed through molecular assay for the detection of Ct infection. Phylogenetic analysis on the ompA gene was performed on Ct positive samples to identify the circulating genovars.

Results: The overall prevalence of Ct-infection was 4.4% (95%CI: 3.2-5.9%): 5.3% among women aged 18-21 years and 3.5% among those aged 22-25 years. Phylogenetic analysis has identified 5 different genovars: D, E, F, G, and H. The most common genovar was the E (46%), followed by genovar F and G (18.9% each), D (13.5%), and H (2.7%).

Conclusions: This study underlines the high prevalence of asymptomatic Ct-infections among young women. Overall, about half of the asymptomatic infections is sustained by genovar E. The introduction in Italy of a systematic screening program should be considered to allow a better understanding of Ct spreading and providing women with an opportunity for early treatment to protect their sexual and reproductive health.

Keywords: C. trachomatis genovars; C. trachomatis infection; Molecular epidemiology; Sexually active asymptomatic young women; Sexually transmitted diseases.

Fig. 1.

Phylogenetic analysis of C. trachomatis partial ompA gene sequences (coded between nt 223-636 of C. trachomatis genovar A, accession number NC007429) obtained during this study and compared to reference sequences. The outcome of the bootstrap analysis is shown next to the nodes, and branch lengths are proportional to genetic distances as indicated by the scale bar. Genovars as well as subgroups are indicated on the right.

Fig. 2.

Genovar distribution among the studied age groups.

Fig. 3.

Overall Ct infection prevalence (line) with 95% CI (vertical lines) and genovar distribution (bars) during the different years of the study. The vertical axis on the left refers to the genovar distribution, while the one on the right refers to prevalence values. NT: not typed.