Background Chlamydia trachomatis is the leading cause of bacterial sexually transmitted diseases (STDs) in industrialised countries. omp1 (ompA), the gene encoding the major outer membrane protein (MOMP), has been widely used for molecular epidemiology, because it contains four spaced variable domains.

Methods A total of 1625 patients attending the STD Outpatients Clinic of St. Orsola University Hospital of Bologna, Italy were enrolled for this study. Each patient was clinically visited, bled in order to perform serological tests, than three urethral or endocervical swabs were obtained. Two swabs were cultured for the detection of C trachomatis and Neisseria gonorrhoeae, whereas the third was stored at −80°C. When a positive result was obtained by C trachomatis culture, the corresponding frozen sample was withdrawn, its DNA was extracted by VERSANT kPCR SP Module (Siemens Healthcare Diagnostics Inc.) and used as a template for omp1 gene fragment amplification. PCR products were purified and both strands were sequenced. Nucleotide sequences were compared to omp1 sequences using the BLAST search tool at the National Center for Biotechnology Information. The sequences were manually aligned using BioEdit (version 7.0.0) software. χ² Test was used and a p value of <0.05 was considered statistically significant.

Results C trachomatis was detected in 103 out of 1625 (6.3%) swabs by culture. Prevalence was significantly higher in men (p<0.01), with 60 positives out of 525 tested (11.4%), than in women (43/1100; 3.9%), as well as presence of clinical symptoms: 81.7% (49/60) of infected men and 44.2% of infected women (19/43) were symptomatic. Also prevalence of STD coinfections was significantly higher (p<0.01) in men (35/60; 58.3%) than in women (8/43; 18.6%). In our population the most common serovar was E, with a prevalence of 38.8%, followed by G (23.3%), F (13.5%), D/Da (11.6%), and J (4.8%). Statistically significant differences (p=0.042) in serovar prevalence between men and women were detected. Finally, significant differences (p=0.035) were detected when serovar distribution among patients with or without coinfection was studied: patients with an infection due to D/Da had the highest coinfection rate (75.0%), whereas coinfection rates among patients with serovars F, E, and G were 57.1%, 37.5%, and 29.2%, respectively see Abstract P3-S1.07 table 1.

Conclusions The present study contributed to increase the knowledge on serovar distribution of C trachomatis in Italy.