Early life antibiotic exposure is associated with an increased risk of atopic eczema and hay fever

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. In this study we aimed to systematically review and quantify the relationship between early life exposure to antibiotics and the risk of atopic eczema (dermatitis) or hay fever (allergic rhinitis). Method: 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. Separate metaanalyses were performed to assess the risk estimates for cohort studies, cross sectional studies and case control studies. Furthermore, in subgroup analyses the effect of child's age at the time of antibiotic use/diagnosis of allergies, and the number of courses of antibiotic treatments have been analyzed. 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 23 studies (including 256 609 patients) to study the risk of hay fever. In all separate meta-analyses of the distinct study designs, those who were exposed to antibiotics early in life were found to have a statistically significantly increased risk of eczema and hay fever. The summary OR for risk of eczema were 1.24 (95% CI, 1.09-1.41; I2: 60.0%) in the meta-analyses of the cohort studies (n = 50 824); 1.41 (95% CI, 1.33-1.49; I2: 0.0%) in the cross sectional studies (n = 217 752), and 1.15 (95% CI, 1.01- 1.42; I2: 79.5%) in the case control studies (n = 125 941). The summary OR for risk of hay fever were 1.18 (95% CI, 1.01-1.37; I2: 74.3%) in the cohort studies (n = 46 540); 1.56 (95% CI, 1.29-1.90; I2: 63.6%) in cross sectional studies (n = 27 608), and 1.14 (95% CI, 1.04-1.26; I2: 64.8%) in the case control studies (n = 182 461). In subgroup analyses, there was no statistically significant effect of the child's age at time of antibiotic use as well as the 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. Conclusion: Early life exposure to antibiotics is related to an increased risk of both atopic eczema and hay fever later in life.