Abstract
This study aims to develop and validate the Post-COVID Symptom Scale for Children/Youth (PCSS-C/Y), which is a comprehensive tool for measuring the symptom burden of post-COVID-19 conditions-persistent symptoms after SARS-CoV-2 infection, commonly known as Long COVID-and its impact on health-related quality of life among children and adolescents. Parents of children and adolescents, adolescents, and young adults with and without a history of COVID-19 were invited to fill in a questionnaire from October 2022 to June 2023. There were 386 valid parent proxy-reported responses, 433 valid adolescent self-reported responses, and 324 valid young adult self-reported responses included in the final analysis. The PCSS-C/Y demonstrated stable factor structure and good internal consistency in different sampling groups. The scale score was negatively associated with Paediatric Quality of Life Inventory (PedsQL) scores (young adult self-report, adjusted R(2) = 0.394; adolescent self-report, adjusted R(2) = 0.219; parent-report, adjusted R(2) = 0.292), while it was positively associated with Strengths and Difficulties Questionnaire (SDQ) scores (young adult self-report, adjusted R(2) = 0.195; adolescent self-report, adjusted R(2) = 0.154; parent-report, adjusted R(2) = 0.239). The scale can also discriminate the post-infected cases and control cases, Cohen's d = 0.41, 0.50, and 0.38 for adult self-report, adolescent self-report, and parent-report, respectively. Conclusions: The PCSS-C/Y is a valid and reliable tool for quantifying the diverse symptomatology of post-COVID-19 conditions in children and adolescents. It provides quantifiable measurements that enable clinicians to monitor post-COVID-19 symptoms in children and young people and facilitates the development of interventions for post-COVID-19 conditions.