Abstract
Superspreading events (SSEs) have characterized previous epidemics of severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) infections1-6. For SARS-CoV-2, the degree to which SSEs are involved in transmission remains unclear, but there is growing evidence that SSEs might be a typical feature of COVID-197,8. Using contact tracing data from 1,038 SARS-CoV-2 cases confirmed between 23 January and 28 April 2020 in Hong Kong, we identified and characterized all local clusters of infection. We identified 4-7 SSEs across 51 clusters (n = 309 cases) and estimated that 19% (95% confidence interval, 15-24%) of cases seeded 80% of all local transmission. Transmission in social settings was associated with more secondary cases than households when controlling for age (P = 0.002). Decreasing the delay between symptom onset and case confirmation did not result in fewer secondary cases (P = 0.98), although the odds that an individual being quarantined as a contact interrupted transmission was 14.4 (95% CI, 1.9-107.2). Public health authorities should focus on rapidly tracing and quarantining contacts, along with implementing restrictions targeting social settings to reduce the risk of SSEs and suppress SARS-CoV-2 transmission.
Highlights
Superspreading is a common feature of past betacoronavirus epidemics of SARS-CoV and MERS-CoV
SARS-CoV-2 exhibits a high degree of individual transmission heterogeneity, and we estimate that 19% of SARS-CoV-2 infections in Hong Kong were responsible for 80% of all transmissions, while 69% of cases did not transmit to anyone
Transmission in social settings was significantly associated with an increased number of secondary cases compared to transmission observed in family households
Summary
Superspreading is a common feature of past betacoronavirus epidemics of SARS-CoV and MERS-CoV. Transmission in social settings was significantly associated with an increased number of secondary cases compared to transmission observed in family households These findings take advantage of the quality of case ascertainment and contact tracing data in Hong Kong, some incompleteness in links between cases could potentially bias our estimates of transmission heterogeneity. These results suggest that reducing the occurrence of superspreading events by limiting gatherings in social settings can have a disproportionate effect on reducing SARS-CoV-2 transmission, which has important policy implications concerning the approach to COVID-19 suppression measures around the world. Received: 19 May 2020; Accepted: 2 September 2020; Published online: 17 September 2020
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