EARLY INDOOR MICROBIAL EXPOSURE LOWERS THE RISK OF ASTHMA

Abstract

Early life exposures to microbial agents such as bacterial endotoxin have been suggested to inhibit the development of atopy and asthma. In this study we assessed the relation between living room floor levels of bacterial endotoxin, fungal β(1,3)-glucan and fungal extracellular polysaccharides (EPS-Pen/Asp) and the development of atopic sensitisation and asthma in 810 infants born from allergic parents. Exposure to microbial agents was determined at 3 months, serum IgE at 12 and 24 months, and asthma symptoms & diagnosis at 12, 24, and 48 months. Low, medium and high exposure groups were defined based on tertiles of the exposure distributions. Analyses were adjusted for gender, pets, ETS, siblings, parental education, and mite allergen levels. Microbial exposure was inversely associated with atopic sensitization at 24 months in a dose dependent manner with ORs ranging from 0.3–0.5 for the highest exposure groups (statistically significant only for EPS-Pen/Asp). A similar but weaker dose response was observed for atopy at 12 months. A doctor's diagnosis of asthma at 48 months was also less common in highly exposed children with ORs ranging from 0.3–0.5, statistically significant (p < 0.01) for endotoxin and EPS. A protective effect in the medium exposure group was also observed but the effect was less pronounced suggesting a dose-response effect. These protective effects on doctor's diagnosed asthma were shown consistently across the three time points, but were statistically significant only at 24 and 48 months. Interestingly, the protective effects of microbial exposure were observed both in atopic and non-atopic asthmatics. Asthma symptoms (wheeze and night cough) in the last 12 months (at age 4) were slightly less prevalent in the high exposure groups (NS). No associations were found for eczema. Endotoxin, EPS-Pen/Asp, and glucan concentrations were highly correlated limiting the potential to study them separately. In conclusion, although our findings need confirmation at older ages, they provide, for the first time, evidence from a prospective cohort study that non-infectious microbial exposure at a very young age may protect from developing atopy and asthma.