Over the last decade, syphilis rates have risen dramatically in many high-income countries, including in England, which has seen a greater than 150% increase. Meanwhile, the burden of syphilis in some resource-constrained settings is still poorly understood. Genomics can enhance epidemiological surveillance, enabling novel insights into transmission which may explain changes in disease burden or guide public health interventions.
Methods:
Over the last 6 years, we have generated a high-level view of T. pallidum genomic diversity in high-income countries, and are currently undertaking prospective studies to do the same in low-and-middle-income countries. To determine if whole genome sequencing could be used to identify discrete patterns of transmission, we linked patient demographic, geospatial and behavioural metadata to whole T. pallidum genomes collected as part of routine surveillance from across England; the same will be done for prospectively collected samples from four African countries. Phylogenomic reconstruction was used to explore putative transmission clusters and facilitate outbreak exclusion.
Results:
Phylogenomic analysis and clustering revealed discrete patterns of circulating T. pallidum sublineages in England, which exhibited different spatiotemporal trends linked to demography or behaviour, suggesting they represent different sexual networks. By focussing on different regions of England we were able to distinguish a local heterosexual transmission cluster from a background of transmission amongst gay, bisexual and other men who have sex with men. Using newly generated data, we will contrast phylogenomic patterns from England to those in Africa.
Conclusion:
Our findings demonstrate that T. pallidum genomics can be used to identify putative transmission clusters for epidemiological follow-up, and therefore has a role to play in informing public health interventions. The generalisability of these insights from high-income to low-income settings needs further evaluation.
