O07.3 Molecular investigation of Treponema pallidum strains associated with ocular syphilis in the United States

Background Ocular syphilis cases continue to be identified in the United States since two clusters were reported in late 2014 into early 2015. Ocular syphilis (OS) is an inflammatory eye condition that can occur at any stage of syphilis with vision loss and blindness reported in some patients. We performed genotyping and whole genome sequencing (WGS) on Treponema pallidum strains from OS cases as part of molecular surveillance activities. Methods A total of 79 specimens from 57 patients with suspected or confirmed OS were received from 14 states between February 2016 and November 2020. Specimens included CSF, whole blood, serum, plasma, vitreous fluid, and a throat swab. T. pallidum DNA was detected with a real-time PCR assay targeting the polA gene. Genotyping was done using the four-component typing scheme (tpr E, G, & J; arp, tp0548, and tp0279). T. pallidum genomic DNA was enriched by selective whole genome amplification (SWGA) using Multiple Displacement Amplification (MDA) with custom oligonucleotides followed by WGS on an Illumina MiSeq v2 500 cycle platform. Results Twenty-three patients (40.4%) were MSM and HIV positive, respectively; 41 (71.9%) identified as White race, 4 (7%) Hispanic, and 3 (5.3%) Black. Twenty-three specimens from 18 (31.6%) patients tested positive for T. pallidum DNA. Thirteen of 23 (56.5%) specimens were CSF, while the remaining 10 included whole blood, serum, vitreous fluid, and a throat swab. Specimens from 3 patients were fully typed, revealing strain types 14b9g, 14d10g, and 14e9f. Six patients had partial genotypes. WGS was successful on 1 CSF and 2 vitreous fluid specimens from 2 cases resulting in 87% – 98% genome coverage with at least 5 reads/site. Phylogenetic analysis showed that the 2 strains belonged to the Street 14 clade. Conclusions Our findings show that multiple strain types are responsible for ocular syphilis in the United States.