Table 1.
Summary of 3,615 strains studied
| Geographic region | Time span | Number of strains |
| Ontario, Canada | 1996–2009 | 346 |
| Denmark | 1973–2013 | 436 |
| East Germany | 1969–1991 | 155 |
| Finland | 1988–2011 | 1106 |
| Iceland | 1988–2010 | 50 |
| Norway | 1997–2009 | 215 |
| Sweden | 1973–2012 | 482 |
| Georgia, USA | 1995–2010 | 340 |
| Minnesota, USA | 1997–2010 | 474 |
| Other | ∼1920s–1980s | 11 |
Information for the complete list of 3,615 strains is found in Dataset S1. Fig. S1 contains specific years included in the study. East Germany refers to the former East Germany. Canada strains were from Ontario. US strains were from Georgia (Atlanta area) and Minnesota. “Other” includes strains of predominantly historic interest.