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’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.
- Communicable diseases
- control of diseases
- public health policy
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YZ and DM contributed equally
Contributors YZ, DM and QW contributed to the study conception and design. Material preparation, data collection and analysis were performed by LJ, YT, YC, SL and PY. The first draft of the manuscript was written by YZ, DM, CRM and LG. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
Funding This study was funded by Capital’s Funds for Health Improvement and Research [grant number 2018-1-1012] and Beijing Science and Technology Planning Project [grant number Z201100005420010].
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; internally peer reviewed.
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