1. 2Department of Mathematics and Statistics, Helsinki Institute of Information Technology (HIIT), FI-00014 University of Helsinki, Finland
2. 1Department of Computer Science, Aalto University, FI-00076 Espoo, Finland
3. 3Pathogen Genomics, Wellcome Trust Sanger Institute, Cambridge CB10 1SA, UK
4. 4Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK
5. 5Department of Biostatistics, University of Oslo, 0317 Oslo, Norway