Association between antibiotic exposure within 6 months of age and severity of AD
According to the SCORAD index, when antibiotic exposure occurred within 6 months of age, 55 patients (66.3%) had mild AD and 28 patients (33.7%) had moderate to severe AD at the age of 1 year. In contrast, when antibiotic exposure did not occur, the severity of AD at 1 year was predominantly mild, accounting for 82.5% of the cases (Table 3, p<0.01). Mean SCORAD score was 9.42 (SD = 10.00) in 1 year children with AD who were exposed to antibiotics, which was significantly higher than that of AD patients who did not have exposure to antibiotics within the first 6 months of life (p=0.02).
Combined effects of IL-13 gene polymorphism and antibiotic exposure within 6 months of age on AD development
We found some evidence for the interaction between genetic polymorphisms and environmental factors on the development of AD (p for interaction=0.06). Compared to infants who were not exposed to antibiotics within the first 6 months of age and had the IL-13(rs20541) GG genotype, those who were exposed to antibiotics and had theIL-13 (rs20541) GA+AA genotype had a higher risk of AD at a young age (Table 4).
Regarding antibiotics, the dose–response relationship was particularly notable in children with IL-13 (rs20541) GA+AA genotype (Fig. E2). The higher the number of prescriptions, the higher was the risk of AD at 2- and 3-year-old children (at 2 years, once: aOR=1.49, 95% CI 0.96–2.32; ≥2 times: aOR=2.00, 95% CI 1.18–3.42; at 3 years, once: aOR=1.57, 95% CI 1.00–2.46; ≥2 times: aOR=1.96, 95% CI 1.13–3.38)