Contact Settings and Risk for Transmission of SARS-CoV-2


Luo L, Liu D, Liao X, et al.


Contact Settings and Risk for Transmission in 3410 Close Contacts of Patients With COVID-19 in Guangzhou, China: A Prospective Cohort Study. Ann Intern Med 2020;Aug 13:[Epub ahead of print].

Summary By:

Salim Hayek, MD, FACC

Quick Takes

  • SARS-CoV-2 transmission is more likely to occur in household contacts compared to health care and public transportation settings.
  • More severe cases and those with a productive cough were more likely to lead to secondary infection.

Study Questions:

What is the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission to close contacts?


The authors traced 3,410 close contacts of 391 coronavirus disease 2019 (COVID-19) cases diagnosed between January 13–March 6, 2020, in Guangzhou, China, leveraging the Centers for Disease Control and Prevention (CDCs) in China, which completes epidemiologic investigations of cases within 24 hours. Close contacts were defined as contacts without effective protection regardless of the duration of exposure with ≥1 persons with COVID-19 any time starting 2 days prior to the onset of symptoms or sampling of laboratory testing. Cell phone tracing was used to identify contacts on public transportation. Close contacts were quarantined for 14 days from the last contact of index cases, and testing for SARS-CoV-2 was performed daily during that time.


Of 3,410 close contacts (52.8% male, median age 38 years), 127 (3.7%) were secondarily infected, of whom eight were asymptomatic. Amongst the 119 symptomatic cases, 20 (16.8%) were mild, 87 (73.1%) were moderate, and 12 (10.1%) were severe. Rate of transmission in asymptomatic cases was low (0.3%), and highest in severe cases (6.2%). The rate of secondary infection was highest in the household (10.3%) compared to health care settings (1.0%) or public transportation (0.1%). Productive cough was associated with a close to 5-fold increase in the odds of secondary infection. The rate of transmission of SARS-CoV-2 did not differ by age or sex.


The overall transmission rate of SARS-CoV-2 is approximately 4% among close contacts of patients with COVID-19, and is higher among household contacts, those with more severe disease, and those with expectoration.


This study leverages the China CDCs and effective contact tracing methods to characterize the rate of transmission of SARS-CoV-2 across different settings. The household contact transmission rate of 10.3% in the study is consistent what has previously been reported both in China and the United States, providing validity to the findings. The low risk of transmission by asymptomatic people and in public transportation and health care settings is reassuring and should address concerns of those who have been reluctant to seek care out of fear of COVID-19 infection.



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