Introduction: Chlamydia trachomatis infection is the most common bacterial sexually transmitted disease (STD) in the world. Multi-locus sequence typing (MLST) is a nucleotide sequence based approach for unambiguously characterising isolates of bacteria and other organisms via the internet, and has been used to monitor the molecular epidemiology of pathogenic bacteria and also to help understand their evolution and population biology. To enrich genetic background information on C. trachomatis in the MLST database and to deepen the current knowledge of the molecular characteristics of C. trachomatis strains circulating in China.

Methods Ninty-nine C. trachomatis-infected patients and 16 follow-up patients were recruited from selected STD clinics in Jiangsu Province and Guangxi Zhuang Autonomous Region, from whom cervical swabs and demographic data were collected. C. trachomatis type was determined by MLST analysis. Chlamydia sequence types from different areas were compared by using Bio-Numerics 7 to generate a minimum spanning tree.

Results Six out of the 16 follow-up samples tested positive for C. Trachomatis DNA. Of 105 Chlamydia-positive samples, 90 (85.71%) were available for MLST analysis, by which seven ompA genovars and 26 MLST types were determined. Significant differences in genovar distribution were not observed between C. trachomatis strains from Jiangsu and Guangxi, but noted between Chinese and Italian strains. Among the six Chlamydia-positive follow-up samples, three were identified as Chlamydia re-infections, while the other three failed to yield an MLST result.

Conclusion The prevalent STs of C. trachomatis in China were different from those in Italy. Half of Chlamydia-positive follow-up samples (3/6) were identified as re-infections; hence, follow-up Chlamydial infected patients deserve more attention of clinicians.