Author contributions
S.S.C., B.J.C. and V.D. designed the study. E.Y.L.C., L.L.M.P., S.L.L. and S.S.C. conducted clinical surveillance. S.G. performed sequencing and analysed the data. S.G., K.M.E. and D.V. designed the figures and wrote the manuscript with contributions from S.S.C and B.J.C. All authors discussed and approved the manuscript.