Household Transmission of SARS-CoV-2, Zhuhai, China, 2020

Household Transmission of SARS-CoV-2, Zhuhai, China, 2020. Spencer EA, Heneghan C.

Published on July 23, 2020

Reference Wu J, Huang Y, Tu C, et al. Household Transmission of SARS-CoV-2, Zhuhai, China, 2020 [published online ahead of print, 2020 May 11]. Clin Infect Dis. 2020;ciaa557. 
Study type
Country China
Setting Household
Funding Details This work was financially supported by grants from the Natural Science Foundation of Guangdong Province of China. Fundamental Research Funds for the Central Universities.
Transmission mode Person to person, Close contact
Exposures Household

Bottom Line

This prospective study of 148 household contacts found a secondary infection rate of 32% within households.

Evidence Summary

This prospective study identified 35 index cases and their 148 household contacts. 

Assuming that all these secondary cases were infected by their index cases, the second infection rate (SIR) in household context was 32% (95% CI, 22% to 44%), with 10% of secondary cases being asymptomatic. 

Multivariate analysis showed that household contacts with underlying medical conditions, a history of direct exposure to Wuhan and its surrounding areas, and sharing a vehicle with an index patient were associated with higher susceptibility.

Household members without protective measures after illness onset of the index patient seem to increase the risk for SARS-CoV-2 infection. 

Separate dining, indoor isolation, ventilation and disinfection, and wearing masks after index case symptom onset were not associated with COVID-19 prevalence (implying presymptomatic transmission).

What did they do?

This study prospectively investigated household transmission of COVID-19 from index cases, using cases identified January to February in Zhuhai, China. 

All consecutive patients with probable or confirmed COVID-19 admitted to the Fifth Affiliated Hospital of Sun Yat-sen University from 17th January to 29th February 2020, were investigated as possible study participants and if eligible were invited to join. 35 index cases and their household contacts were identified and enrolled into the study. Participants were interviewed and completed questionnaires for demographic and clinical data collection.  Household contacts were then prospectively followed via active symptom monitoring for 21 days. Nasopharyngeal and/or oropharyngeal swabs were collected at 3-7 days intervals. 

A household was defined as two or more people living together in the same indoor living

space. A household index was the first person to introduce SARS-CoV-2 into the household.

Household contacts were defined as person who spent at least one night in the house after the

symptom onset of the index patient. It was assumed that all household secondary cases were generated by their corresponding index cases and ignored infections acquired from outside the household (community infections) or the possibility of tertiary or higher infection. 

Secondary infection rate (SIR) within a household was defined as the number of confirmed secondary cases of SARS-CoV-2 in the household within 21 days after index case isolation, divided by the total number of contacts in that household. The incubation period of SARS-CoV-2 was calculated as the number of days between the earliest and latest dates of exposure after index patient onset and the date of the secondary case onset. The serial interval was estimated by identifying the number of days between the reported onset date in the household contact and the reported onset date for that household’s index case patient.

Study reliability

This was a relatively small study. 

All these secondary cases were assumed to be infected by their index cases within the household.

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

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.