Inferring Timing of Infection Using Within-host SARS-CoV-2 Infection Dynamics Model: Are ""Imported Cases"" Truly Imported?

Keisuke Ejima; Kwang Su Kim; Yusuke Ito; Shoya Iwanami; Hirofumi Ohashi; Yoshiki Koizumi; Koichi Watashi; Ana I Bento; Kazuyuki Aihara; Shingo Iwami

Expected day of infection establishment 72 Figure 1A depicts the weekly epidemic curve in Singapore from January 21 st to March 15 th 73 based on symptom onset and laboratory confirmation. Because the laboratory test is performed 74 after symptom onset, the epidemic curve based on laboratory confirmation follows the curve based 75 on symptom onset. For the first few weeks, the epidemic in Singapore was not in the phase of 76 exponential growth, which suggests secondary transmissions are limited and any long chains of 77 transmission did not succeed yet. The first 18 cases discussed here are in the first two weeks of 78 the epidemic. Here we assessed whether the 12 initial 'imported' cases were in fact imported or the result 90 of ongoing transmission in Singapore. We found that 6 of 12 cases were clearly infected before 91 arrival to Singapore, the other however have likely been infected after the arrival to Singapore. 92