Molecular Subtyping of Treponema pallidum during a Local Syphilis Epidemic in Men Who Have Sex with Men in Melbourne, Australia

Treponema pallidum is the causative agent of syphilis, a sexually transmitted infection of significant public health importance. Since 2000 there has been a marked increase in the number of cases of syphilis infections notified in Victoria, Australia, with the majority of cases occurring in men who have sex with men (MSM) and the highest incidence being in HIV-infected MSM. The molecular subtyping method described by Pillay et al. (A. Pillay et al., Sex. Transm. Dis. 25:408–414, 1998) has been used in this study to determine the diversity of T. pallidum subtypes circulating locally and to look for any relationship between T. pallidum subtypes and HIV status over a 6-year period (2004 to 2009). Treponema pallidum DNA was detected in 303 patient specimens (n = 3,652), and full subtyping profiles were obtained from 90 of these (from 88 patients). A total of 11 T. pallidum subtypes were identified: types 14e (28, 31.1%), 14d (15, 16.7%), 14k (13, 14.4%), 14p (12, 13.3%), 14i (7, 7.8%) 14b (6, 6.7%), 14l (5, 5.6%), and 12i, 13b, 13i, and 13e (1 each, 1.1%). This study showed a similar level of variation among circulating T. pallidum strains compared with that in other studies using the same methodology. A different mix of strains and different predominating strains have been found at each geographical study location, with type 14e emerging as the predominant local strain in Victoria. There was no detectable trend between T. pallidum subtypes and the specimen collection site or stage of syphilis (where known), nor was there any relationship between particular strains and HIV status.