Abstract
Initial cases of coronavirus disease in Hong Kong were imported from mainland China. A dramatic increase in case numbers was seen in February 2020. Most case-patients had no recent travel history, suggesting the presence of transmission chains in the local community. We collected demographic, clinical, and epidemiologic data from 50 patients, who accounted for 53.8% of total reported case-patients as of February 28, 2020. We performed whole-genome sequencing to determine phylogenetic relationship and transmission dynamics of severe acute respiratory syndrome coronavirus 2 infections. By using phylogenetic analysis, we attributed the community outbreak to 2 lineages; 1 harbored a common mutation, Orf3a-G251V, and accounted for 88.0% of the cases in our study. The estimated time to the most recent common ancestor of local coronavirus disease outbreak was December 24, 2019, with an evolutionary rate of 3.04 × 10−3 substitutions/site/year. The reproduction number was 1.84, indicating ongoing community spread.
Highlights
Initial cases of coronavirus disease in Hong Kong were imported from mainland China
In Hong Kong, the first imported case was identified on January 23, 2020; the case-patient was a resident of mainland China who traveled to Hong Kong from Wuhan through Shenzhen by high-speed rail
Clinical, and epidemiologic data of 50 hospitalized patients who accounted for 53.8% of COVID-19 cases in Hong Kong at the data cutoff point (February 28, 2020), including 3 imported cases and 6 transmission clusters of local infections
Summary
Initial cases of coronavirus disease in Hong Kong were imported from mainland China. The estimated time to the most recent common ancestor of local coronavirus disease outbreak was December 24, 2019, with an evolutionary rate of 3.04 × 10−3 substitutions/site/year. The first local case with unknown source (i.e., patient who had no travel record during the 14-day incubation period) was reported on February 4, 2020 [6]. By February 28, 2020, a total of 93 COVID-19 cases had been recorded in Hong Kong; >70 (75.3%) of those were local cases and those case-patients’ close contacts [6,7]. Because source of infection is unknown in most index cases in these clusters, hidden transmission chains were believed to be present in the community
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