Late Breaking Abstract - Early-life antibiotic exposure and development of diseases in childhood - a nationwide registry study

<bold>Objective:</bold> This study aimed to investigate the association between early-life antibiotic exposure and the development of immune-mediated diseases (IMDs) in children and young adults, while also applying a sibling design to mitigate the influence of familial factors and unmeasured confounding. <bold>Design:</bold> Data from national Danish registries were used. Antibiotic exposure before one year of age was defined from prescription records. Outcomes of asthma, allergy, eczema, celiac disease, juvenile arthritis, overweight, and type 1 diabetes were identified from hospital and prescription records. <bold>Participants:</bold> The study population consisted of 518,483 children born between 1998 - 2006. On average, children were followed for 13.2 years. Approximately 40% (n=209,013) of children were exposed to systemic antibiotics before the age of one. <bold>Main Outcome:</bold> The risk of developing immune-mediated diseases in the full population, as well as a sibling-matched design, was assessed with Cox regression. <bold>Results:</bold> Early antibiotic exposure was significantly associated with an increased risk of several IMDs (adjusted Hazard Ratios (aHR) 1.25 - 1.52). A dose-response relationship was observed. When analyzing sibling pairs, only asthma and eczema outcomes (aHR 1.07-1.35) were associated with antibiotic exposure. <bold>Conclusions:</bold> Early-life antibiotic exposure is linked to immune-mediated diseases in childhood and young adulthood, but familial and unmeasured factors within the family context may provide partial explanations. The study emphasizes the need to better understand the interplay between antibiotics, familial proneness and immune-mediated pathogenesis to identify potential preventive strategies.