Early-Life Exposure to Antibiotics and Risk for Crohn's Disease: A Nationwide Danish Birth Cohort Study.

BACKGROUND Early-life antibiotic use can alter the intestinal flora and modify the risk of developing Crohn disease (CD), but rigorous epidemiological evidence is limited, with inconsistent results. METHODS We identified all children born in Denmark from 1995 to 2009 and followed them from birth until death, emigration, a diagnosis of CD, or January 1, 2013. Using Cox regression, we assessed the association between antibiotic exposure in the first year of life and subsequent risk for CD, adjusting for sex, degree of urbanization, birth order, birth year, route of delivery, gestational age, smoking during pregnancy, intake of nonsteroidal anti-inflammatory drugs in the first year of life, and family history of CD. RESULTS During a median 9.5 years (9.3 million total person-years), CD was diagnosed in 208 of 979,039 children. Antibiotic use in the first year of life was associated with a higher risk of CD (adjusted hazard ratio, 1.4; 95% confidence interval [CI], 1.1-1.8), with the highest risk with ≥6 courses of antibiotics (adjusted hazard ratio, 4.1; 95% CI, 2.0-8.5). A family history of CD did not modify these risk associations. The cumulative risk of CD at the 11th birthday for children exposed to antibiotics in their first year of life was 0.16‰ (95% CI, 0.11‰-0.22‰) compared to 0.11‰ (95% CI, 0.08‰-0.15‰) for children unexposed to antibiotics in their first year of life. CONCLUSIONS Antibiotic use in the first year of life is associated with a modestly increased risk for CD, although the absolute risk is very low.