Crowding and the shape of COVID-19 epidemics by Rader, B, Scarpino, SV, Nande, A, Hill, AL, Adlam, B, Reiner, RC, Pigott, DM, Gutierrez, B, Zarebski, AE, Shrestha, M, Brownstein, JS, Castro, MC, Dye, C, Tian, H, Pybus, OG, Kraemer, MUG