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

Abstract

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. Findings: Among 11,818 laboratory confirmed cases of COVID-19 diagnosed till 13 th 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). Interpretation: 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. Funding: Health and Medical Research Fund Commissioned Research on Control of Infectious Disease (see acknowledgments for full list).

Household Secondary Attack Rates of SARS-CoV-2 by Variant and Vaccination Status

“…We identified 2097 records (1791 from PubMed, 306 from medRxiv, and 2 from reference lists of eligible articles) published between June 18, 2021, and March 8, 2022 (eFigure 1 in the Supplement ). Fifty-eight new studies 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 (eTable 2 in the Supplement ) were combined with 77 studies from ou...…”

“…This reflects new variants and changing vaccination coverage. From highest to lowest, the overall household SARs were 42.7% (95% CI, 35.4%-50.4%) for Omicron (7 studies 55 , 61 , 62 , 63 , 64 , 67 , 68 ), 36.4% (95% CI, 33.4%-39.5%) for Alpha (11 studies 18 , 19 , 21 , 23 , 28 , 33 , 44 , 46 , 49 , 50 , 69 ), 29.7% (95% CI, 23.0%-37.3%) for Delta (16 studies 18 , 20 , 24 , 26 , 35 , 37 , 42 , 46 , 50 , 55 , 57 , 61 , 64 , 65 , 66 , 70 ), and 22.5% (95% CI, 18.6%-26.8%) for Beta (3 studies 15 , 18 , 50 ) ( Figure 2 ). High heterogeneity was found among studies for Omicron ( I 2 = 98.2%; P < .001) and Delta ( I 2 = 99.1%; P < .001), moderate for Alpha ( I 2 = 59.6%; P < .001), and low for Beta ( I 2 = 2.6%; P = .79).…”

Outbreak investigation of airborne transmission of Omicron (B.1.1.529) - SARS-CoV-2 variant of concern in a restaurant: Implication for enhancement of indoor air dilution

“…Despite some sporadic episodes of SARS-CoV-2 transmission in the designated quarantine hotels between quarantinees,( Wong et al, 2021 , Wong et al, 2021 ) these did not result in a new wave of COVID-19 in our community. Cheng et al, (2021) …”

Boosting SARS-CoV-2 detection combining pooling and multiplex strategies

“…At this point of the pandemic, the rapid detection of new cases and the surveillance needed for restoring normal activities are important for monitoring new waves of infection. Cheng and collaborators demonstrated that mass testing for contact tracing combined with phylogenetic analysis prevent new infections in Hong Kong besides its contributions to genomic surveillance of new SARS-CoV-2 variants 13 .…”