• Gilbert T Chua, Joshua Sung Chih Wong, Ivan Lam, Polly Po Ki Ho, Wai Hung Chan, Felix Yat Sun Yau, Rosa DuqueJaime SJSDepartment of Paediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China., Alvin Chi Chung Ho, Ka Ka Siu, Tammy W Y Cheung, David Shu Yan Lam, Victor Chi Man Chan, Kwok Piu Lee, Kwing Wan Tsui, Tak Wai Wong, Man Mut Yau, Tsz Yan Yau, Kate Ching Ching Chan, Michelle Wai Ling Yu, Chit Kwong Chow, Wah Keung Chiu, Kwok Chiu Chan, WongWilfred H SWHSDepartment of Paediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China., Marco Hok Kung Ho, Winnie W Y Tso, Keith T S Tung, Christina S Wong, Janette Kwok, Wing Hang Leung, Jason C Yam, WongIan C KICKCentre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy, University of Hong Kong, Hong Kong Special Administrative Region, China.Research Department of Practice and Policy, UCL School of Pharmacy, University, Paul Kwong Hang Tam, ChanGodfrey Chi FungGCFDepartment of Paediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China., Chun Bong Chow, ToKelvin K WKKWDepartment of Microbiology, Carol Yu Centre for Infection, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China., Yu Lung Lau, Kwok Yung Yuen, Patrick Ip, and Mike Yat Wah Kwan.
• Department of Paediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China.
• JAMA Netw Open. 2021 May 3; 4 (5): e218824.

ImportanceSchools were closed intermittently across Hong Kong to control the COVID-19 outbreak, which led to significant physical and psychosocial problems among children and youths.ObjectiveTo 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 ParticipantsThis 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 MeasuresDemographic 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.ResultsAmong 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 RelevanceThis 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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