Spatiotemporal reconstruction of the introduction of hepatitis C virus into Scotland and its subsequent regional transmission

A more comprehensive understanding of hepatitis C virus (HCV) transmission dynamics could facilitate public health initiatives to reduce the prevalence of HCV in people who inject drugs. We aimed to determine how HCV sequences entered and spread throughout Scotland and to identify transmission hot spots. A Scottish data set with embedded demographic data was created by sequencing the NS5B of 125 genotype 1a (Gt1a) samples and 166 Gt3a samples and analyzed alongside sequences from public databases. Applying Bayesian inference methods, we reconstructed the global origin and local spatiotemporal dissemination of HCV in Scotland. Scottish sequences mainly formed discrete clusters interspersed between sequences from the rest of the world; the most recent common ancestors of these clusters dated to 1942 to 1952 (Gt1a) and 1926 to 1942 (Gt3a), coincident with global diversification and distribution. Extant Scottish sequences originated in Edinburgh (Gt1a) and Glasgow (Gt3a) in the 1970s, but both genotypes spread from Glasgow to other regions. The dominant Gt1a strain differed between Edinburgh (cluster 2 [C2]), Glasgow (C3), and Aberdeen (C4), whereas significant Gt3a strain specificity occurred only in Aberdeen. Specific clusters initially formed separate transmission zones in Glasgow that subsequently overlapped, occasioning city-wide cocirculation. Transmission hot spots were detected with 45% of samples from patients residing in just 9 of Glasgow's 57 postcode districts. HCV was introduced into Scotland in the 1940s, concomitant with its worldwide dispersal likely arising from global-scale historical events. Cluster-specific transmission hubs were identified in Glasgow, the key Scottish city implicated in HCV dissemination. This fine-scale spatiotemporal reconstruction improves understanding of HCV transmission dynamics in Scotland. IMPORTANCE HCV is a major health burden and the leading cause of hepatocellular carcinoma. Public health needle exchange and "treatment as prevention" strategies targeting HCV are designed to reduce prevalence of the virus in people who inject drugs (PWID), potentially mitigating the future burden of HCV-associated liver disease. Understanding HCV transmission dynamics could increase the effectiveness of such public health initiatives by identifying and targeting regions playing a central role in virus dispersal. In this study, we examined HCV transmission in Scotland by analyzing the genetic relatedness of strains from PWID alongside data inferring the year individuals became infected and residential information at a geographically finer-scale resolution than in previous studies. Clusters of Scotland-specific strains were identified with regional specificity, and mapping the spread of HCV allowed the identification of key areas central to HCV transmission in Scotland. This research provides a basis for identifying HCV transmission hot spots.