Epidemiology and transmission of COVID-19 in Shenzhen, China

COVID-19: Epidemiology and transmission of COVID-19 in Shenzhen, China. Spencer EA, Heneghan C


Published on June 30, 2020

Reference Bi Q, Wu Y, Mei S, et al. Epidemiology and transmission of COVID-19 in 391 cases and 1286 of their close contacts in Shenzhen, China: a retrospective cohort study [published online ahead of print, 2020 Apr 27]. Lancet Infect Dis. 2020;S1473-3099(20)30287-5.  2020
Study type
Country China
Setting Shenzhen
Funding Details Emergency Response Program of Harbin Institute of Technology, Emergency Response Program of Peng Cheng Laboratory, US Centers for Disease Control and Prevention.
Transmission mode Close contact
Exposures Household

Bottom Line

Case isolation and contact tracing reduces the time during which cases are infectious in the community.

Evidence Summary

356 out of 391 cases (91%) had mild or moderate clinical severity at initial assessment. 

Household contacts and those travelling with a case were at higher risk of infection, Odds Ratio  6.27 (95%CI 1.49 to 26.33) for household contacts and 7.06 (95%CI 1.43 to 34.91) for those travelling with a case compared to other close contacts. 

The household secondary attack rate was 11.2% (95%CI 9.1 to 13.8), and children were as likely to be infected as adults (infection rate 7.4% in children <10 years vs population average of 6.6%). 

What did they do?

Between 14th January and 12th February 2020, the Shenzhen Center for Disease Control and Prevention identified 391 SARS-CoV-2 cases and 1286 close contacts. 

The authors compared cases identified through symptomatic surveillance and contact tracing, and estimated the time from symptom onset to confirmation, isolation, and admission to hospital. 

They estimated metrics of disease transmission and analysed factors influencing transmission risk.

Study reliability

Protocols for data collection altered over time, e.g. the definition of a confirmed case changed on 7th February, towards the end of data collection, to require symptoms – sensitivity analyses showed that truncating the data at this point did not qualitatively influence results.

It is not possible to identify all of a person’s contacts. There was also uncertainty in the number of asymptomatic cases missed by surveillance

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes Yes Unclear Yes Yes

What else should I consider?

COVID-19 had a fairly short incubation period (mean 4–6 days) but a long clinical course. These findings represent one region at one time in the pandemic and although informative may not represent other situations. For example how individuals self-isolate may have changed over time, and hygiene measures such as handwashing may have altered.

About the authors

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Elizabeth Spencer

Dr Elizabeth Spencer; MMedSci, PhD. Epidemiologist, Nuffield Department for Primary Care Health Sciences, University of Oxford.