@article {Zhang84, author = {Yi Zhang and David Muscatello and Yi Tian and Yanwei Chen and Shuang Li and Wei Duan and Chunna Ma and Ying Sun and Shuangsheng Wu and Lin Ge and Peng Yang and Lei Jia and Quanyi Wang and Chandini Raina MacIntyre}, title = {Role of presymptomatic transmission of COVID-19: evidence from Beijing, China}, volume = {75}, number = {1}, pages = {84--87}, year = {2021}, doi = {10.1136/jech-2020-214635}, publisher = {BMJ Publishing Group Ltd}, abstract = {Background The presymptomatic transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been documented in limited clusters, and it is predicted through modelling. However, there is a lack of evidence from observations with a large sample size.Methods We used data from meticulous contact tracing of people exposed to cases of SARS-CoV-2 to estimate the proportion of cases that result from the presymptomatic transmission of the virus in Beijing during January 2020 and February 2020.Results The results showed that presymptomatic transmission occurred in at least 15\% of 100 secondary COVID-19 cases. The earliest presymptomatic contact event occurred 5 days prior to the index case{\textquoteright}s onset of symptoms, and this occurred in two clusters.Conclusions The finding suggested that the contact tracing period should be earlier and highlighted the importance of preventing transmission opportunities well before the onset of symptoms.}, issn = {0143-005X}, URL = {https://jech.bmj.com/content/75/1/84}, eprint = {https://jech.bmj.com/content/75/1/84.full.pdf}, journal = {Journal of Epidemiology \& Community Health} }