Ragonnet-Cronin M, et al. - Considering the possibility of identifying factors associated with increased transmission risk using molecular epidemiological analysis of viral pathogens, researchers examined a large dataset of NS34A, NS5A, and NS5B viral sequences from patients with chronic hepatitis C virus (HCV) genotypes 1-6 infection for the frequency of genetic clustering. The analysis of 7,457 patients with chronic HCV infection suggested 256 clusters comprising 541 patients (7.3%). They noted increased clustering frequency, an indicator of increased transmission risk, in correlation to HCV/HIV co-infection, young age, and high HCV viral load. Considering the previous work on HCV/HIV co-infection in acute HCV cohorts, they suggest patients with HCV/HIV co-infection as the possible disproportionate source of new HCV infections and recommend preparing the treatment efforts towards elimination in this vulnerable population.