A cluster epidemic of COVID-19 in a supermarket in Liaocheng, Shandong Province.

COVID-19: A cluster epidemic of COVID-19 in a supermarket in Liaocheng, Shandong Province. Spencer EA, Heneghan C.


Published on July 8, 2020

Reference Zhang JZ, Zhou P, Han DB et al. Investigation of a cluster epidemic of COVID-19 in a supermarket in Liaocheng, Shandong Province. Zhonghua Liu Xing Bing Xue Za Zhi. 2020;41(0):E055. See: http://rs.yiigle.com/yufabiao/1191303.htm 2020
Study type
Country China
Setting Supermarket
Funding Details Non reported
Transmission mode Person to person, Close contact
Exposures Supermarket

Bottom Line

Several cases were apparently transmitted from a supermarket worker.

Evidence Summary

Between 30th January to 9th February, 8,437 people were screened. These included 120 supermarket employees, 93 family members, and 8,224 supermarket shoppers. 

Twenty-five cases of SARS-CoV-2 were identified, with clusters of cases in four families. The total infection rate was 0.30% (25/8437). Three cases (12% of all infections identified) were asymptomatic 

Infection rates among supermarket employees were 9.2% (11/120), family members of confirmed cases 2.9% (12/93) and supermarket clients 0.02% (2/8 224) respectively. 

The Supermarket is located in the commercial centre of Liaocheng DC District, with 52 regular employees and 68 temporary employees. 

The supermarket has 2 floors, a small area, and a compact space distribution in each area, and staff often communicate in close proximity. 

Ten infected supermarket employees worked on the first floor, the case worked in the Fresh vegetable delivery staff – in the vegetable area on the second floor and the delivery area on the first floor. 

The incubation period of the first-generation cases was eight days; in the second-generation cases, supermarket customers No. 12 and 13 were single exposures, the incubation period of No. 12 cases was seven days, and the No. 13 cases are asymptomatic infections; of the third-generation cases, family members for a single exposure, the incubation period was ten days. 

What did they do?

This study explored a cluster of cases of COVID-19 in Liaocheng city, China, looking to identify the chain of transmission.  

The first confirmed case (case 1), as a supermarket employee, became ill on January 27, 2020, was hospitalized on 28th and was diagnosed on 30th. It was a local case with no history of travel or close contact

Close contacts and family members were tracked and screened on 1st February 2020. Close contacts included supermarket employees, family members having contact history with related cases between 13th and 26th January, supermarket clients between 16th and 30th January and family members of related cases. 

Nasopharyngeal swabs were collected and real-time fluorescence quantitative RT-PCR was used to detect nucleic acids of SARS-CoV-2. 

Study reliability

This is a moderately-sized study in a particular setting. Additional studies are needed to understand if these findings are replicable.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes No Unclear Yes Unclear

What else should I consider?

The paper was translated using google translate.

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.