Chlamydia trachomatis Serovars Causing Urogenital Infections in Women in Melbourne, Australia

Studies on the prevalence of Chlamydia trachomatis serovars and genotypes could improve our understanding of C. trachomatis epidemiology and transmission. There have been few studies characterizing C. trachomatis detected in clinical specimens in Australia (4, 7). In one study of C. trachomatis among men who have sex with men (MSM) in Melbourne, Australia, it was reported that serovar D was predominant (54%), followed by G and J (4). For comparison with the serovar distribution among MSM in Melbourne (4), we used omp1 sequencing to determine the serovars of C. trachomatis consecutively detected in specimens from 56 women attending gynecological clinics in Melbourne (May to July and October to December 2003). This project was sanctioned by the Royal Women's Hospital Human Research Ethics Committee and the Victorian Department of Human Services Human Research Ethics Committee.

(All of the information in this letter has been presented at the 13th International Union against Sexually Transmitted Infections (IUSTI) Asia Pacific Conference 2004, 6 to 9 July 2004, Chiang Mai, Thailand.)

From these women, 60 C. trachomatis-positive specimens were stored after COBAS Amplicor PCR testing performed by the Royal Women's Hospital Molecular Microbiology Unit, Melbourne, Australia (urine = 30, cervical swab = 19, high-vaginal swab = 9, urethral swab = 1, throat swab = 1).

omp1 PCR has a lower sensitivity in comparison to the plasmid-directed COBAS Amplicor PCR (5, 6), and past work has shown a higher yield of confirmation for COBAS Amplicor PCR with a nested protocol (5). Hence, for this study a nested omp1 PCR was used to achieve a higher amplicon yield for sequencing. DNA extraction, nested omp1 PCR with primers NL-f and NL-r (4), and DNA sequencing of PCR products were performed as described previously (4).

Of the 60 specimens, 47 (78%) were positive by the nested omp1 PCR. Despite a second round of PCR, one NLf/r-positive sample was not included for sequencing as the estimated concentration of DNA was below the threshold for the sequencing reaction. Future work should seek to perform multiple PCRs on samples with low amplicon yields.

A total of 46 samples from 42 women underwent sequencing of the NLf/r omp1 fragment, and the sequencing results were compared to known omp1 nucleotide sequences in the GenBank databases (http://www.ncbi.nlm.nih.gov/BLAST/) to determine the corresponding serovars. No mixed infections of more than one serovar were observed for this sample of women, and only one sample per patient was used in the analysis (Table 1). Sequence analysis showed that the most prevalent omp1 sequences corresponded to serovar E (17, 40%), followed by F (8, 19%), G (7, 17%), J (4, 10%), D (3, 7%), and K (3, 7%). These findings are consistent with serovar distributions reported for other developed countries where serovar E has been identified as the most prevalent (3, 8).

TABLE 1.

C. trachomatis serovar distribution among 42 women tested at Royal Women's Hospital clinics and serovar distribution among 39 MSM tested in male-only saunas in Melbourne, Australia

Deduced serovar	No. (%) of:		P value
	MSM (n = 39)a	Women (n = 42)b
B complex
B	1 (3)	0	NCc
D	21 (54)	3 (7)	<0.000
E	1 (3)	17 (40)	<0.000
Intermediate group
F	1 (3)	8 (19)	0.018
G	10 (26)	7 (17)	0.322
C complex
H	1 (3)	0	NC
J	4 (10)	4 (10)	0.912
K	0	3 (7)	NC

^aMSM were tested at male-only saunas in Melbourne, Australia (5). Of this sample of MSM, the chlamydia serovar was determined from 29 chlamydia-positive anal swabs, nine urine samples, and three throat swabs (this includes one man with a chlamydia-positive anal swab and urine sample with the same serovar detected).

^bNo mixed infections of more than one serovar were detected for this sample of women. Of women who had more than one urogenital specimen collected, the same serovar was determined for each specimen.

^cNC, not calculated.

The serovar distribution of chlamydia among this sample of women is significantly different from the distribution of serovars causing urogenital infections among MSM in Melbourne (Table 1), in particular the differences in the most successful serovars (as measured by the most prevalent serovars). Different serovars identified from heterosexually acquired chlamydia and MSM-acquired chlamydia have also been reported by Barnes and colleagues (1) and Geisler and colleagues (2). Although it is difficult to interpret these findings using a small and relatively uncharacterized population of women, this study has highlighted several areas for future research on C. trachomatis epidemiology and transmission.

Future research could investigate the possible explanations for this phenomenon, such as transmission pathways or sexual networks (heterosexual versus MSM), tissue tropism, or perhaps other confounding ligands that may be responsible for directing colonization of various tissues. It is also likely that patient characteristics are a key component to understanding the different serovar distributions in women and MSM, such as age, history of chlamydial infections, sexualbehavior, and presence or absence of symptoms. A comprehensive study with a large and diverse study population may offer fresh insight into chlamydial infections in Australia.