Multiple microbial exposures in the home may protect against asthma or allergy in childhood

Background Experimental animal data on the gram-negative bacterial (GNB) biomarker endotoxin suggest that persistence, dose, and timing of exposure are likely to influence its effects on allergy and wheeze. In epidemiologic studies, endotoxin may be a sentinel marker for a microbial milieu, including gram-positive bacteria (GPB) as well as GNB, that may influence allergy and asthma through components (pathogen-associated molecular patterns) that signal through innate Toll-like receptor pathways. Objective To determine the influence of current GNB and GPB exposures on asthma and allergic sensitization in school-aged children. Methods We examined the relationship between bacterial biomarkers and current asthma and allergic sensitization in 377 school-aged children in a birth cohort study. We then evaluated the effects of school-aged endotoxin, after controlling for exposure in early life. Results Exposure to GNB was inversely associated with asthma and allergic sensitization at school age [for >median endotoxin: prevalence odds ratio (POR) = 0.34, 95% CI = 0.2-0.7, for current asthma and prevalence ratio = 0.77, 95% CI = 0.6-0.97, for allergic sensitization]. In contrast, elevated GPB in the bed was inversely associated with current asthma (POR = 0.41, 95% CI = 0.2-0.9) but not with allergic sensitization (POR = 1.07, 95% CI = 0.8-1.4). School-aged endotoxin exposure remained protective in models for allergic disease adjusted for early-life endotoxin. Conclusion Both GNB and GPB exposures are associated with decreased asthma symptoms, but may act through different mechanisms to confer protection. Endotoxin exposure in later childhood is not simply a surrogate of early-life exposure; it has independent protective effects on allergic disease.