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Clinical Characteristics and Transmission of COVID-19 in Children and Youths During 3 Waves of Outbreaks in Hong Kong

Educational Objective
To identify the key insights or developments described in this article
1 Credit CME
Key Points

Question  What were the major sources of infection among children and youths with COVID-19 in Hong Kong in 2020?

Findings  In this cross-sectional study of 397 children and youths with COVID-19 in the first 3 waves of outbreaks in Hong Kong, in 2020, the largest group had no recent international travel, and nearly all individuals were reported to have other family members with COVID-19. Three students studying in the same school contracted COVID-19, and few children or youths with no recent international travel reported unknown contact histories.

Meaning  These findings suggest that households and not schools were the major route of transmission among children and youths with COVID-19 in Hong Kong.

Abstract

Importance  Schools were closed intermittently across Hong Kong to control the COVID-19 outbreak, which led to significant physical and psychosocial problems among children and youths.

Objective  To compare the clinical characteristics and sources of infection among children and youths with COVID-19 during the 3 waves of outbreaks in Hong Kong in 2020.

Design, Setting, and Participants  This cross-sectional study involved children and youths aged 18 years or younger with COVID-19 in the 3 waves of outbreaks from January 23 through December 2, 2020. Data were analyzed from December 2020 through January 2021.

Main Outcomes and Measures  Demographic characteristics, travel and contact histories, lengths of hospital stay, and symptoms were captured through the central electronic database. Individuals who were infected without recent international travel were defined as having domestic infections.

Results  Among 397 children and youths confirmed with COVID-19 infections, the mean (SD) age was 9.95 (5.34) years, 220 individuals (55.4%) were male, and 154 individuals (38.8%) were asymptomatic. There were significantly more individuals who were infected without symptoms in the second wave (59 of 118 individuals [50.0%]) and third wave (94 of 265 individuals [35.5%]) than in the first wave (1 of 14 individuals [7.1%]) (P = .001). Significantly fewer individuals who were infected in the second and third waves, compared with the first wave, had fever (first wave: 10 individuals [71.4%]; second wave: 22 individuals [18.5%]; third wave: 98 individuals [37.0%]; P < .001) or cough (first wave: 6 individuals [42.9%]; second wave: 15 individuals [12.7%]; third wave: 52 individuals [19.6%]; P = .02). Among all individuals, 394 individuals (99.2%) had mild illness. One patient developed chilblains (ie, COVID toes), 1 patient developed multisystem inflammatory syndrome in children, and 1 patient developed post–COVID-19 autoimmune hemolytic anemia. In all 3 waves, 204 patients with COVID-19 (51.4%) had domestic infections. Among these individuals, 186 (91.2%) reported having a contact history with another individual with COVID-19, of which most (183 individuals [90.0%]) were family members. In the third wave, 18 individuals with domestic infections had unknown contact histories. Three schoolmates were confirmed with COVID-19 on the same day and were reported to be close contacts.

Conclusions and Relevance  This cross-sectional study found that nearly all children and youths with COVID-19 in Hong Kong had mild illness. These findings suggest that household transmission was the main source of infection for children and youths with domestic infections and that the risk of being infected at school was small.

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Article Information

Accepted for Publication: March 5, 2021.

Published: May 3, 2021. doi:10.1001/jamanetworkopen.2021.8824

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Chua GT et al. JAMA Network Open.

Corresponding Authors: Mike Yat Wah Kwan, MSc, MRCPCH, Paediatric Infectious Disease Unit, Department of Paediatrics and Adolescent Medicine, 3/F, Block S, Hospital Authority Infectious Disease Centre, Princess Margaret Hospital, 2-10, Princess Margaret Hospital Rd, Lai Chi Kok, Hong Kong Special Administrative Region, China (kwanyw1@ha.org.hk); Patrick Ip, MPH, Department of Paediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, 1/F, New Clinical Building, Queen Mary Hospital, 102 Pokfulam Rd, Pokfulam, Hong Kong Special Administrative Region, China (patricip@hku.hk).

Author Contributions: Dr Kwan had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Drs Chua and J. S. C. Wong were co-first authors.

Concept and design: Chua, I. Lam, W. H. Chan, Siu, D. S. Y. Lam, V. C. M. Chan, Chiu, Tso, C. S. Wong, I. C. K. Wong, Tam, G. C. F. Chan, C. B. Chow, Lau, Ip, Kwan.

Acquisition, analysis, or interpretation of data: Chua, J. S. C. Wong, I. Lam, P. P. K. Ho, W. H. Chan, F. Y. S. Yau, Rosa Duque, A. C. C. Ho, Siu, Cheung, D. S. Y. Lam, V. C. M. Chan, Lee, Tsui, T. W. Wong, M. M. Yau, T. Y. Yau, K. C. Chan, Yu, C. K. Chow, K. C. C. Chan, W. H. S. Wong, M. H. K. Ho, Tso, Tung, C. S. Wong, Kwok, Leung, Yam, Tam, C. B. Chow, To, Yuen, Ip, Kwan.

Drafting of the manuscript: Chua, I. Lam, Yu, C. S. Wong, Ip, Kwan.

Critical revision of the manuscript for important intellectual content: Chua, J. S. C. Wong, I. Lam, P. P. K. Ho, W. H. Chan, F. Y. S. Yau, Rosa Duque, A. C. C. Ho, Siu, Cheung, D. S. Y. Lam, V. C. M. Chan, Lee, Tsui, T. W. Wong, M. M. Yau, T. Y. Yau, K. C. Chan, C. K. Chow, Chiu, K. C. C. Chan, W. H. S. Wong, M. H. K. Ho, Tso, Tung, C. S. Wong, Kwok, Leung, Yam, I. C. K. Wong, Tam, G. C. F. Chan, C. B. Chow, To, Lau, Yuen, Ip, Kwan.

Statistical analysis: Chua, Rosa Duque, W. H. S. Wong, Kwan.

Obtained funding: Tso, Ip, Kwan.

Administrative, technical, or material support: J. S. C. Wong, I. Lam, P. P. K. Ho, Cheung, V. C. M. Chan, T. W. Wong, T. Y. Yau, K. C. Chan, Yu, C. K. Chow, K. C. C. Chan, Tso, G. C. F. Chan, Kwan.

Supervision: J. S. C. Wong, P. P. K. Ho, F. Y. S. Yau, Siu, Tsui, T. W. Wong, M. H. K. Ho, Tso, I. C. K. Wong, Tam, C. B. Chow, Lau, Ip, Kwan.

Conflict of Interest Disclosures: Dr I. C. K. Wong reported receiving funding from the Hong Kong government. Dr G. C. F. Chan reported serving as scientific advisor for Xellera and Pangenia. No other disclosures were reported.

Funding/Support: This study was supported by Collaborative Research Fund (CRF) 2020/21 and One-off CRF Coronavirus and Novel Infectious Diseases Research Exercises grant No. C7149-20G.

Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

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