Allergies, antibiotics use, and multiple sclerosis.

BACKGROUND: The associations between allergies, antibiotics use, and multiple sclerosis (MS) remain controversial and their mediating or moderating effects have not yet been examined. We aimed to assess the direct and indirect influences of allergies and antibiotics use on MS development, and their interactions.

METHODS: A 1:3 matched case-control study was performed using the National Ambulatory Medical Care Survey database from 2006 to 2013 in the USA. Multiple sclerosis was identified based on the ICD-9 code (340.0) in any position. Cases were matched to their controls based on survey year, age, gender, race, payer type, region, and tobacco use. Allergy diseases and antibiotics prescriptions were extracted by ICD-9 code and drug classification code, respectively. Both generalized structural equation model and MacArthur approach were used to examine their intrinsic relationships.

RESULTS: The weighted prevalence of MS was 133.7 per 100,000 visits. A total of 829 MS patients and 2441 controls were matched. Both respiratory tract allergies (OR = 0.29, 95% CI: 0.18, 0.49) and other allergies (OR = 0.38, 95% CI: 0.19, 0.77) were associated with a reduction of the risk of MS. Patients with respiratory tract allergies were more likely to use penicillin (OR = 8.73, 95% CI: 4.12, 18.53) and other antibiotics (OR = 3.77, 95% CI: 2.72, 5.21), and those with other allergies had a higher likelihood of penicillin use (OR = 4.15, 95% CI: 1.27, 13.54); however, the link between antibiotics use and MS was not confirmed although penicillin use might mediate the relationship between allergies and MS.

CONCLUSIONS: The findings supported allergy as a protective factor for MS development. We also suggest antibiotics use might not be a suitable indicator of bacterial infection to investigate the cause of MS.