This is a preprint. Preprints are preliminary reports that have not undergone peer review. They should not be considered conclusive, used to inform clinical practice, or referenced by the media as validated information.
Research Article

Clustering and superspreading potential of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in Hong Kong

Dillon Adam, Peng Wu, Jessica Wong, Eric Lau, Tim Tsang, Simon Cauchemez, Gabriel Leung, Benjamin Cowling
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Superspreading events have characterised previous epidemics of severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) infections. Using contact tracing data, we identified and characterized SARS-CoV-2 clusters in Hong Kong. Given a superspreading threshold of 6-8 secondary cases, we identified 5-7 probable superspreading events and evidence of substantial overdispersion in transmissibility, and estimated that 20% of cases were responsible for 80% of local transmission. Among terminal cluster cases, 27% (45/167) ended in quarantine. Social exposures produced a greater number of secondary cases compared to family or work exposures (p<0.001) while delays between symptom onset and isolation did not reliably predict the number of individual secondary cases or resulting cluster sizes. Public health authorities should focus on rapid tracing and quarantine of contacts, along with physical distancing to prevent superspreading events in high-risk social environments. 

Keywords
coronavirus, SARS-CoV-2, COVID-19, superspreading, transmission, public health
Comment moderated
on 04 June, 2020
Aravindan Veiraiah
ORCiD
commented on 05 June, 2020

It would be helpful for an international audience to describe the methodology of contract tracing. How well were contacts of asymptomatic contacts traced? What is the risk that spread via asymptomatic contact of asymptomatic contact was attributed erroneously to a symptomatic person? If that risk was high, clusters thought to be due to super spreader events might have actually been a collection of clusters of spread by asymptomatic contacts. What are the other limitations of this methodology?

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This is a preprint. It has not completed peer review.
Research Article

Clustering and superspreading potential of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in Hong Kong

Dillon Adam, Peng Wu, Jessica Wong, Eric Lau, Tim Tsang, Simon Cauchemez, Gabriel Leung, Benjamin Cowling

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This manuscript passed our Prescreen assessment

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Superspreading events have characterised previous epidemics of severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) infections. Using contact tracing data, we identified and characterized SARS-CoV-2 clusters in Hong Kong. Given a superspreading threshold of 6-8 secondary cases, we identified 5-7 probable superspreading events and evidence of substantial overdispersion in transmissibility, and estimated that 20% of cases were responsible for 80% of local transmission. Among terminal cluster cases, 27% (45/167) ended in quarantine. Social exposures produced a greater number of secondary cases compared to family or work exposures (p<0.001) while delays between symptom onset and isolation did not reliably predict the number of individual secondary cases or resulting cluster sizes. Public health authorities should focus on rapid tracing and quarantine of contacts, along with physical distancing to prevent superspreading events in high-risk social environments. 

Comment moderated
on 04 June, 2020
Aravindan Veiraiah
ORCiD
commented on 05 June, 2020

It would be helpful for an international audience to describe the methodology of contract tracing. How well were contacts of asymptomatic contacts traced? What is the risk that spread via asymptomatic contact of asymptomatic contact was attributed erroneously to a symptomatic person? If that risk was high, clusters thought to be due to super spreader events might have actually been a collection of clusters of spread by asymptomatic contacts. What are the other limitations of this methodology?

Comments can take the form of short reviews, notes or questions to the author. Comments will be posted immediately, but removed and moderated if flagged.