Risk factors for SARS-CoV-2 infection and hospitalisation in children and adolescents in Norway: A nationwide population-based study

Objective To determine risk factors for SARS-CoV-2 infection and hospitalisation among children and adolescents. Design Nationwide, population-based cohort study. Setting: Norway from 1 March 2020 to 31 April 2021. Participants: All Norwegian residents <18 years of age. Main outcome measures Population-based health care and population registries were used to study risk factors for SARS-CoV-2 infection, including socioeconomic factors, country of origin, and pre-existing chronic comorbidities. All residents were followed until age 18, emigration, death, or end of follow-up. Hazard ratios (HR) estimated by Cox regression models were adjusted for testing frequency. Further, risk factors for admission to the hospital among the infected were investigated. Results Of 1 182 796 residents, 22608 (1.9%) tested positive by polymerase chain reaction or lateral flow tests, of whom 107 (0.5%) were admitted to a hospital. Low family income (aHR 1.40, 95% confidence interval 1.36 to 1.46), crowded housing (1.35, 1.30 to 1.39), household size, age, and area of living were independent risk factors for infection. A non-Nordic country of origin was the strongest risk factor (aHR 2.37, 95% CI 2.30 to 2.49), whereas chronic comorbidity was not associated with the risk of infection. Chronic comorbidity was associated with hospitalisation (aHR 4.15, 2.63 to 6.56), in addition to age, whereas socioeconomic status and country of origin did not predict hospitalisation among those infected. Conclusions Socioeconomic factors, country of origin, and area of living were associated with the risk of SARS-CoV-2 infection. However, these factors did not predict hospitalisation among those infected. Chronic comorbidity was associated with the risk of admission but not with the overall risk of acquiring SARS-CoV-2. What is already known on this topic Hospital admissions rates for covid-19 among children and adolescents are low compared to adults. Admission rates to hospitals and intensive care units for covid-19 have been higher in minority groups and in children and adolescents with chronic comorbidity. Whether underlying differences in susceptibility for severe disease or the incidence of infections are driving these associations have not been investigated. What this study adds Low family income, crowded housing and household size, and country of origin outside the Nordic countries were associated with increased risk of infection with SARS-CoV-2. None of these factors, but chronic comorbidities, were associated with the risk of hospital admission among those infected.