Fig. 1

Transmission diagram for 78 confirmed patients infected with COVID-19. The red circle represents the asymptomatic carrier of COVID-19. The red ball represents the time that patient is confirmed positive by both symptoms and rRT-PCR assay. The grey balls with letter C means the contact time of eight patients (passage 2) with Patient 1. The dark blue balls represents eight patients of passage 2 (Patient A to H, respectively). The purple balls represents twenty-three patients of passage 3 (Patient A1 to H2, respectively). The light blue balls represents forty-six patients of passage 4 (Patient A1a to H2b, respectively). The grey dotted line represents the incubation time for passage 2 (Patient A to H). The red lines, blue dotted lines and purple dotted lines represent the transmission from passage 1 to passage 2, from passage 2 to passage 3 and from passage 3 to passage 4. Due to the comparatively large numbers of passage 3 and 4, the incubation time from passage 2 to passage 3 and from passage 3 to passage 4 is not included in this chart. The detailed information for the incubation time are listed on Table 1