Nat. Med. https://doi.org/10.1038/s41591-020-1092-0 (2020)
Analysis of contact-tracing data of 1,038 laboratory-confirmed cases of SARS-CoV-2 infection in Hong Kong between January and April revealed a striking pattern. The authors estimate that 80% of the cases were seeded by just 19% of the infected people; conversely, the majority of patients failed to infect even one other person.
The majority of infector–infected transmission pairs identified (92 of 169) involved household contacts, but transmission in external social settings was not far behind (56 of 169). Notably, although the median size was two, the largest cluster (defined as “two or more confirmed infections with close contact”) involved 106 cases linked to four Hong Kong bars with live music — although the authors could not conclusively demonstrate this, this points toward one (or more) infectious band member(s). Two other large clusters were tied to a wedding and a temple. Overall, social settings were associated with younger patients and more secondary infections.
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Carvalho, T. COVID-19 clusters. Nat Med 26, 1806 (2020). https://doi.org/10.1038/s41591-020-01159-8