Endotoxin Exposure and Childhood Wheeze and Asthma: A Meta-Analysis of Observational Studies

Abstract

Background. Exposure to endotoxin has been widely investigated as a potential factor for asthma and associated symptoms in children with different results. To clarify a potential relationship, we performed the present meta-analysis to integrate the results of studies examining the association of endotoxin exposure with wheeze and asthma in children. Methods. A search for relevant studies and reviews was conducted in MEDLINE, Highwire, CINAHL, and The Cochrane Library databases. Adjusted odds ratio (OR) with corresponding 95% confidence interval (CI) for endotoxin exposure and wheeze or asthma were retrieved and pooled to generate summary effect estimates in STATA 11.1. Results. Nineteen studies were included in the meta-analysis. The summary estimates suggested that endotoxin was positively associated with wheeze in infants and toddlers (meta-OR: 1.48, 95% CI: 1.10–1.98), but negatively related to asthma in school-aged children (meta-OR: 0.82, 95% CI: 0.69–0.97 for endotoxin concentration and 0.68, 95% CI: 0.50–0.93 for endotoxin load). Conclusions. Based on the studies evaluated, endotoxin is a risk factor for wheeze in younger children, but a protective factor for asthma in older children. Thus, this study supports the “hygiene hypothesis.”