ABSTRACT
Background SARS-CoV-2 clinical presentation is associated with the patients' age group. Overall, young individuals present higher proportions of asymptomatic or mild COVID-19 infection, compared to adults. Data on secondary COVID-19 transmission in households, according to the cases' age group, are accumulating. Methods A follow-up cohort study including all COVID-19 RT-PCR -confirmed cases (adolescent students and school staff) diagnosed in an epidemiological investigation of a large high school outbreak. We compared the adolescent and adult groups regarding clinical symptoms, time to negative COVID-19 RT-PCR tests and infection transmission in households. Results The study population included 817 persons. The confirmed COVID-19 RT-PCR outbreak cases (n=178) were followed (students aged 12-19 years, median age 14 years, n=153, school staff aged 24-67 years, median age 39 years, n=25) and the cases' household close contacts (n=639) were tested. The adolescents had lower symptomatic infection rates, shorter time to negative COVID-19 RT-PCR tests and lower transmission rates to household members, compared to the adults. The general transmission rate among household contacts was 13.5%, (86/639) ranging from 8.6% in asymptomatic students' contacts to 27.3% in symptomatic staff contacts. COVID-19 transmission rates were significantly higher in contacts of symptomatic cases compared to asymptomatic cases (Odds Ratio: 2.06, 95%CI 1.26-3.4) and higher in adults compared to adolescents (Odds Ratio: 2.69, 95%CI 1.43-4.89). Conclusions Adolescents and adults diagnosed in an outbreak investigation differ as to COVID-19 clinical presentation and transmission. As adolescents may show mild or no symptoms, COVID-19 prevention in school settings is challenging. Implementing non-pharmaceutical measures and promoting vaccination programs in eligible staff and students should be considered. Graphical abstract Image, graphical abstract