Close Contacts, Infected Cases, and the Trends of SARS-CoV-2 Omicron Epidemic in Shenzhen, China

Abstract

(1) The overall trends of the number of daily close contacts and infected cases as well as their association during an epidemic of Omicron Variant of SARS-CoV-2 have been poorly described. (2) Methods: This study was to describe the trends during the epidemic of the Omicron variant of SARS-CoV-2 in Shenzhen, China, including the number of close contacts and infected cases as well as their ratios by days and stages (five stages). (3) Results: A total of 1128 infected cases and 80,288 close contacts were identified in Shenzhen from 13 February 2022 to 1 April 2022. Before the citywide lockdown (14 March), the number of daily close contacts and infected cases gradually increased. However, the numbers showed a decrease after the lockdown was imposed. The ratio of daily close contacts to daily infected cases ranged from 20.2:1 to 63.4:1 and reached the lowest during the lockdown period. The growth rate of daily close contacts was consistent with those of infected cases observed 6 days later to some extent. (4) Conclusions: The Omicron variant epidemic was promptly contained by tracing close contacts and taking subsequent quarantine measures.

Keywords: COVID-19; China; Omicron; strategy.

Figure 1

Ratios of the number of daily close contacts and infected cases during the Omicron epidemic in Shenzhen, China, in the spring of 2022. (Note: The grey area indicates the citywide lockdown period.).

Figure 2

Ratios of the number of daily close contacts and infected cases by different stages during the Omicron epidemic in Shenzhen, China, in the spring of 2022. (Note: The grey area indicates the citywide lockdown period.)

Figure 3

Ratios of the number of daily close contacts and infected cases by different stages during the Omicron epidemic in Shenzhen, China, in the spring of 2022.

Figure 4

Spearman’s correlation coefficient between the growth rate of daily close contacts (before lockdown) and infected cases by different lag time number of daily close contacts and the number of daily infected cases, by different lag days.

Figure 5

Radar chart of the growth rate of daily close contacts (before lockdown) and infected cases by different lag times. (Note: Each number in the figure corresponds to a single date. For example, in the radar figure for a lag of 6 days, number 1 indicates 2/14 for the growth rate of daily close contacts, whereas it also means 2/20 (lag of 6 days) for the growth rate of infected cases.)