Fig. 2

Immigration and emigration rates of HCV1a strains from and to Italy, over time period 1940–2015. Left panel: Over 99% of exportation events from Italy are directed towards other European countries (in blue). Note that the rate decline in the most recent years reflects the loss of branches in the sampling time period, rather than the start of an actual tendency. Right panel: The origin of virtually all strains entering Italy can be traced back to the United States (US) and other European countries (see Table 2). At the onset of the Italian HCV1a epidemic, immigration was most intense from the US (in blue). From 1970 onwards, introductions from the European continent started to dominate (in red). The introduction rate (y-axis) was defined as the median posterior estimate of the expected number of migration events from that particular location per time unit