Chlamydia trachomatis serovar distribution in the age of molecular testing

Background: Chlamydia trachomatis (CT) is the agent of the most prevalent bacterial sexually transmitted infection (STI) worldwide. Genotyping of CT strains is important to monitor contact tracing and to enable association with epidemiological and clinical findings. The aim of this study was to assess CT infection prevalence and investigate serovar distribution in a group of high-risk subjects compared to general population in the North of Italy. Material/methods: From January 2011 to May 2014, data about all the consecutive clinical samples submitted to the Microbiology Laboratory of St.Orsola Hospital of Bologna for CT detection were collected. The specimens were obtained from patients attending the STI Outpatients Clinic of the Hospital (high-risk population) or from subjects attending gynecologic clinics or general practitioners offices (low-risk population). All the specimens were tested by the Versant CT/GC DNA 1.0 Assay (Siemens), a duplex real-time PCR simultaneously revealing the presence of CT and Neisseria gonorrhoeae (GC) DNA. In case of a CT positive result, molecular genotyping based on omp1 gene semi-nested PCR followed by RFLP analysis was performed. Results: During the study period, a total of 9315 samples, including 8918 specimens from urogenital sites and 397 from extra-genital localizations (pharyngeal and rectal swabs) were collected from 8906 patients. Subjects attending the STI Outpatients Clinic (N=4081; 2195 males) were younger compared to unselected patients (N=4825; 621 males) (mean age: 32 vs 36; P<0.0001). Total prevalence of CT infection was 8% with a significant difference between the two groups (13% in the high-risk vs 3.8% in the low-risk; P<0.0001) and, globally, positive subjects were younger compared to negative ones (30years vs 35 years; P<0.0001). In contrast to general population, among the high-risk patients CT was mainly diagnosed in males (62.5% vs 27.2%; P<0.0001). GC co-infection was detected in 6.4% of CT positive patients, mainly in males (P<0.0001). The most common serovar in our population was E (42,6%), followed by F (14.7%), G (14%) and D (11.7%). Serovar distribution was influenced by sex (P=0.0018) and age (P<0.0001), while no differences werefound comparing high-risk and low-risk populations (P=0.13). Finally, L2 serovar was detected only on rectal and pharyngeal swabs from MSM (men having sex with men) belonging to the high-risk population. Conclusions: In the present study we were able to highlight significant differences regarding CT prevalence and serovar distribution on the basis of epidemiological characteristics. It should be underlined that on pharyngeal and rectal swabs obtained from high-risk subjects genotyping is fundamental in order to rule out Lymphogranuloma Venereum infection, since the treatment for LGV is different from that for non-LGV Chlamydia.