Investigating the effect of early life antibiotic use on asthma and allergy risk in over 600 000 Canadian children: a protocol for a retrospective cohort study in British Columbia and Manitoba.

introductionAllergic conditions, such as asthma, hay fever and eczema, are some of the most common conditions impacting children globally. There is a strong incentive to study their determinants to improve their prevention. Asthma, hay fever and eczema are influenced through the same immunological pathway and often copresent in children ('the atopic march'). Increasing evidence shows a link between infant antibiotic use and the risk of childhood atopic conditions, mediated through gut microbial dysbiosis during immune system maturation, however, the potential for confounding remains. This study will investigate the relationship between infant antibiotic use and risk of allergic conditions in British Columbian and Manitoban children born over 10 years, adjusting for relevant confounders. METHODS AND ANALYSIS: Provincial administrative datasets will be linked to perform comparable retrospective cohort analyses, using Population Data BC and the Manitoba Population Research Data Repository. All infants born between 2001 and 2011 in BC and Manitoba will be included (approximately 460 000 and 162 500 infants, respectively), following up to age 7. Multivariable logistic regression will determine the outcome risk by the fifth birthday among children who did and did not receive antibiotics before their first birthday. Clinical, demographic and environmental covariates will be explored, and sensitivity analyses performed to reduce confounding by indication. ETHICS AND DISSEMINATION: The University of British Columbia Research Ethics Board (H19-03255) and University of Manitoba Ethics Board (HS25156 (H2021:328)) have approved this study. Data stewardship committees for all administrative datasets have granted permissions, facilitated by Population Data BC and the Manitoba Centre for Health Policy. Permissions from the Canadian Health Infant Longitudinal Development Study are being sought for breastfeeding data (CP185). Findings will be published in scientific journals and presented at infectious disease and respiratory health conferences. A stakeholder committee will guide and enhance sensitive and impactful communication of the findings to new parents.