The association of early life exposure to antibiotics and the development of asthma, eczema and atopy in a birth cohort: confounding or causality?

Studies reporting positive associations between antibiotic exposure and respiratory and allergic disease have been unable to determine the nature of this association. In a birth cohort study, reported antibiotic exposure was monitored before 3 months and before 15 months along with outcomes (wheeze, asthma, eczema, rash, inhaler use) at 15 months (n=1011) and 4 years (n=986). Significant univariate associations of antibiotic exposure before 3 months with asthma developing between birth and 15 months [OR 2.32 (95% CI 1.45–3.69)] were observed. After adjustment for chest infections, this association reduced becoming marginally significant (P=0.07). A marginally significant association of antibiotics with atopy in the univariate analysis also reduced after adjustment for chest infections (OR=1.36, 95% CI 0.91–2.05). There was no effect of antibiotic exposure before 15 months on asthma developing after 15 months and present between 3 and 4 years (OR=1.35 95% CI 0.85–2.14). Antibiotic exposure before 3 months was not associated with eczema and rash developing between birth and 15 months but exposure before 15 months was related to eczema and rash developing after 15 months and remaining present at 4 years. The findings suggest that the effect of antibiotics on respiratory disease may be due to confounding by chest infections at an early age when asthma may be indistinguishable from infection. Clinical & Experimental Allergy Volume. 2008;38(8):1318-24.