Background: Infections, early life exposures and the microbiome have been associated with the aetiology of multiple sclerosis (MS). Data on any possible roles of antibiotics is scarce and conflicting.

Objective: The objective of this study was to investigate associations between outpatient systemic antibiotic exposure and the risk of MS in a nationwide case-control setting.

Methods: Patients with MS were identified from the nation MS registry and their exposure to antibiotics was compared with that of persons without MS, provided by the national census authority. Antibiotic exposure was investigated using the national prescription database and analyzed by Anatomical Therapeutic Chemical (ATC) category.

Results: Among the 1830 patients with MS and 12765 control persons, there were no associations between exposure to antibiotics in childhood (5-9 years) or adolescence (10-19 years) and the subsequent risk of MS. There was also no association between antibiotic exposure 1-6 years before disease onset and the risk of MS, save for exposure to fluoroquinolones in women (odds ratio: 1.28; 95% confidence interval: 1.03, 1.60; p = 0.028) which is probably associated with the increased infection burden in the MS prodrome.

Conclusion: Use of systemic prescription antibiotics was not associated with subsequent MS risk.