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. 2024 Jun 21:8:100525.
doi: 10.1016/j.puhip.2024.100525. eCollection 2024 Dec.

An observational study on imported COVID-19 cases in Hong Kong during mandatory on-arrival hotel quarantine

Mario Martín-Sánchez  1 , Peng Wu  1   2 , Dillon C Adam  1 , Bingyi Yang  1 , Wey Wen Lim  1 , Yun Lin  1 , Eric H Y Lau  1   2 , Sheena G Sullivan  3   4 , Gabriel M Leung  1   2 , Benjamin J Cowling  1   2
Affiliations

An observational study on imported COVID-19 cases in Hong Kong during mandatory on-arrival hotel quarantine

Mario Martín-Sánchez et al. Public Health Pract (Oxf). .

Abstract

Background: Hong Kong enforced stringent travel restrictions during the COVID-19 pandemic. Understanding the characteristics of imported COVID-19 cases is important for establishing evidence-based control measures.

Methods: Retrospective cohort study summarising the characteristics of imported cases detected in Hong Kong between 13 November 2020 and 31 January 2022, when compulsory quarantine was implemented.

Findings: A total of 2269 imported COVID-19 cases aged 0-85 years were identified, of which 48.6 % detected on arrival. A shorter median delay from arrival to isolation was observed in Delta and Omicron cases (3 days) than in ancestral strain and other variants cases (12 days; p < 0.001). Lower Ct values at isolation were observed in Omicron cases than in ancestral strain or other variants cases. No Omicron cases were detected beyond 14 days after arrival. Cases detected after 14 days of quarantine (n=58, 2.6 %) were more likely asymptomatic at isolation and had higher Ct value during isolation, some of them indicating re-positivity or post-arrival infections.

Conclusions: Testing inbound travellers at arrival and during quarantine can detect imported cases early, but may not prevent all COVID-19 introductions into the community. Public health measures should be adapted in response to the emergence of SARS-CoV-2 variants based on evidence from ongoing surveillance.

Keywords: COVID-19; Coronavirus; Imported case; Quarantine; Travel.

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Conflict of interest statement

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: BJC consults for AstraZeneca, Fosun Pharma, GlaxoSmithKline, Moderna, Pfizer, Roche, and Sanofi Pasteur. SGS has served (unpaid) on advisory boards for Sanofi and Seqirus. The authors report no other potential conflicts of interest.

Figures

Fig. 1
Fig. 1
Number of imported COVID-19 cases identified in Hong Kong from 13 November 2020 through 31 January 2022 by week of isolation (A), weekly imported cases per 1000 arrivals to Hong Kong International Airport and weekly cases worldwide (B) and number of imported cases by week of isolation for the most common countries of origin (C).
Fig. 2
Fig. 2
Differences across SARS-CoV-2 variants among imported COVID-19 cases identified in Hong Kong in days from arrival to admission for isolation (A), RT-PCR Ct-value at admission for isolation (B), days from isolation to negative RT-PCR (C) and minimum RT-PCR Ct-value during isolation (D).
Fig. 3
Fig. 3
Number of imported cases with Omicron and other SARS-CoV-2 variants identified in Hong Kong by day from arrival to isolation and day from arrival to symptom onset, and RT-PCR Ct-value at isolation of the imported cases by day from arrival to admission for isolation. Horizontal lines indicate RT-PCR Ct-value at 33 (samples with very low viral load, the criterion used for release of isolation during specific time periods) and 30 (samples with low viral load, indicating a possible re-positive result i.e., long-term intermittent shedding).
Fig. 4
Fig. 4
Kaplan-Meier curves for the time from isolation to first RT-PCR result with Ct value at 33 or above among imported COVID-19 cases identified in Hong Kong by: (A) presence of symptoms; (B) moment of detection; (C) type of SARS-CoV-2; (D) vaccination status including receipt of mRNA vaccination (BNT162b2), inactivated vaccine (CoronaVac), or other vaccine types.
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