Biomaterial Database

Complementation of contact tracing by mass testing for successful containment of beta COVID-19 variant (SARS-CoV-2 VOC B.1.351) epidemic in Hong Kong. 2021

Vincent Chi-Chung Cheng, and Gilman Kit-Hang Siu, and Shuk-Ching Wong, and Albert Ka-Wing Au, and Cecilia Suk-Fun Ng, and Hong Chen, and Xin Li, and Lam-Kwong Lee, and Jake Siu-Lun Leung, and Kelvin Keru Lu, and Hazel Wing-Hei Lo, and Evelyn Yin-Kwan Wong, and Shik Luk, and Bosco Hoi-Shiu Lam, and Wing-Kin To, and Rodney Allan Lee, and David Christopher Lung, and Mike Yat-Wah Kwan, and Herman Tse, and Shuk-Kwan Chuang, and Kelvin Kai-Wang To, and Kwok-Yung Yuen

Infection Control Team, Queen Mary Hospital, Hong Kong West Cluster, Hong Kong Special Administrative Region, China.

BACKGROUND Global dissemination of SARS-CoV-2 Variants of Concern (VOCs) remains a concern. The aim of this study is to describe how mass testing and phylogenetic analysis successfully prevented local transmission of SARS-CoV-2 VOC in a densely populated city with low herd immunity for COVID-19. METHODS In this descriptive study, we conducted contact tracing, quarantine, and mass testing of the potentially exposed contacts with the index case. Epidemiological investigation and phylogeographic analysis were performed. RESULTS Among 11,818 laboratory confirmed cases of COVID-19 diagnosed till 13th May 2021 in Hong Kong, SARS-CoV-2 VOCs were found in 271 (2.3%) cases. Except for 10 locally acquired secondary cases, all SARS-CoV-2 VOCs were imported or acquired in quarantine hotels. The index case of this SARS-CoV-2 VOC B.1.351 epidemic, an inbound traveler with asymptomatic infection, was diagnosed 9 days after completing 21 days of quarantine. Contact tracing of 163 contacts in household, hotel, and residential building only revealed 1 (0.6%) secondary case. A symptomatic foreign domestic helper (FDH) without apparent epidemiological link but infected by virus with identical genome sequence was subsequently confirmed. Mass testing of 0.34 million FDHs identified two more cases which were phylogenetically linked. A total of 10 secondary cases were identified that were related to two household gatherings. The clinical attack rate of household close contact was significantly higher than non-household exposure during quarantine (7/25, 28% vs 0/2051, 0%; p<0.001). CONCLUSIONS The rising epidemic of SARS-CoV-2 VOC transmission could be successfully controlled by contact tracing, quarantine, and rapid genome sequencing complemented by mass testing. BACKGROUND Health and Medical Research Fund Commissioned Research on Control of Infectious Disease (see acknowledgments for full list).