Early life antibiotic exposure is associated with an increased risk of allergy

Background: Several studies suggested that early life exposure to antibiotics is associated with an increased risk of developing allergies later in life, but results are inconsistent. Methods & Design: PubMed and Web of Science databases were searched for observational studies published from January 1966 through November 11, 2015. Studies were included that assessed the association between antibiotic consumption during the first 2 years of life and the risk of eczema or hay fever later in life. Overall pooled estimates of the odds ratios (ORs) were obtained using fixed or random-effects models. Results: Twenty-two studies (including 394,517 patients) were selected to study the risk of eczema and 22 studies (including 256,609 patients) to study the risk of hay fever. The summary ORs for risk of eczema were 1.24 (95% CI, 1.09-1.41; I2: 60.0%) in the meta-analyses of the cohort studies; 1.41 (95% CI, 1.33-1.49; I2: 0.0%) in the cross sectional studies, and 1.15 (95% CI, 1.01-1.42; I2: 79.5%) in the case control studies. The summary ORs for risk of hay fever were 1.18 (95% CI, 1.01-1.37; I2: 74.3%) in the cohort studies; 1.56 (95% CI, 1.29-1.90; I2: 63.6%) in cross sectional studies, and 1.14 (95% CI, 1.04-1.26; I2: 64.8%) in the case control studies. In subgroup analyses, there was no statistically significant effect of the patient's age at both time of antibiotic use and time of allergy diagnosis on these associations. The association was stronger if patients had been treated with ≥ 2 courses compared with one course of antibiotics both for eczema and for hay fever. Conclusions: Early life exposure to antibiotics is related to an increased risk of both eczema and hay fever later in life.