Abstract
BACKGROUND: Early childhood infections remain major contributors to the global disease burden in children under five years of age. Beyond their acute effects, such infections may influence susceptibility to non-communicable diseases later in life. It was hypothesized that common early childhood infections are associated with an increased risk of chronic diseases during adolescence. METHODS: A 18-year, nationwide, population-based cohort study was conducted using the Korean National Health Information Database (2002-2019), including 3,942,947 children aged 0-4 years (2002-2006) at baseline who were followed until ages 13-17 years (2016-2019). Cox proportional hazards models were used to estimate associations between early childhood infections and subsequent adolescent chronic diseases, adjusting for age and gender. RESULTS: Acute upper respiratory tract infections (URTI) at multiple sites (9.7%) and acute nasopharyngitis (9.2%) were the most prevalent infections in early childhood. In adolescence, allergic rhinitis (2.6%) and chronic sinusitis (0.9%) were most frequent. Early-life acute URTI at multiple sites was modestly associated with adolescent allergic rhinitis (HR: 1.03, 95% CI: 1.00-1.06), while acute laryngitis and tracheitis was associated with chronic bronchitis (HR: 1.09, 95% CI: 1.00-1.20) and acute enteritis was associated with chronic noninfective gastroenteritis and colitis (HR: 1.21, 95% CI: 1.06-1.40). Stratified analyses demonstrated slightly stronger associations among boys for allergic rhinitis and urticaria and among girls for chronic noninfective gastroenteritis and colitis. CONCLUSION: In this nationwide cohort, early childhood respiratory and gastrointestinal infections were consistently associated with chronic conditions such as allergic rhinitis, bronchitis, and gastroenteritis and colitis in adolescents. These findings suggest potential early-life origins of chronic disease and highlight the need for targeted prevention strategies to reduce the long-term burden of chronic illnesses in children.