Exposure to microbial agents in house dust and wheezing, atopic dermatitis and atopic sensitization in early childhood: a birth cohort study in rural areas

Abstract

Summary Background Early‐life exposure to environmental microbial agents may be associated with development of wheezing and allergic diseases. Objective To assess the association of microbial exposure in rural homes with the risk of asthma, wheezing, atopic dermatitis and sensitization. Methods Birth cohorts of rural children (n = 1133), half from farmer families, were followed up from birth to 2 years of age by questionnaires in five European centres. Endotoxin and extracellular polysaccharides (EPS) of Penicillium and Aspergillus spp. were determined from living room floor and mother's mattress dust samples collected at 2 months of age. Specific IgE against 19 allergens was measured at 1 year of age. Discrete‐time hazard models, generalized estimations equations (GEE) and logistic regression were used for statistical analyses. Results The incidence of asthma was inversely associated with the amount of dust (adjusted odds ratio (aOR) 0.73, 95% CI 0.58–0.93) and the loads (units/m2) of EPS (aOR 0.75, 95% CI 0.55–1.04) and endotoxin (aOR 0.79, 95% CI 0.60–1.05) in the mother's mattress. Similar associations were seen with wheezing and with living room floor dust. The microbial markers were highly correlated and their effects could not be clearly separated. The inverse associations were seen especially among non‐farmers. The risk of sensitization to inhalant allergens increased with increasing endotoxin exposure from mattress dust. No associations were observed with concentrations (units/g) or with atopic dermatitis. Conclusion and Clinical Relevance The amount and microbial content of house dust were inversely associated with asthma and wheezing, but due to high correlations between microbial agents and amount of dust, it was not possible to disentangle their individual effects. New ways to better measure and represent exposure to environmental microbes, including indexes of biodiversity, are needed especially among farmers.

Exposure to household endotoxin and total and allergen-specific IgE in the US population

“…The 'hygiene hypothesis', which posits that a lack of early childhood exposure to infectious agents increases susceptibility to allergic diseases, has been proposed as a possible explanation for this paradox (Strachan, 2000), although a consensus has yet to be reached. Despite the intriguing hypothesis, findings regarding the endotoxin-allergy relationship in adults and children have been inconsistent (Gehring et al, 2004;Karvonen et al, 2012;Liebers et al, 2006;Park et al, 2001;Thorne et al, 2005). Further study is required to clarify the role of endotoxin in the development of allergen tolerance and the influence of endotoxin on the sensitizing allergic response in the general population.…”

Sleeping on animal fur is related to asthma outcomes in later childhood

“…It has been suggested that ongoing contact with livestock, contact with animal feed, and the consumption of unprocessed cow's milk during pregnancy and infancy might be particularly decisive for the observed protective effects [1]. Subsequently, the "farm environment" has been more specifically described by measuring microbial agents in settled house dust samples [2][3][4]. In this context, there is a common consensus that the time-window comprising pregnancy and early infancy seems to be crucial, where the biological diversity might have the potential to shape the child's immune response by upregulating the innate immunity receptors [1].…”

Mortality in Asthma-Chronic Obstructive Pulmonary Disease Overlap in the United States

“…517 The risk of asthma is also reduced in children whose bedrooms have high levels of bacterial-derived lipopolysaccharide endotoxin. 518,519 Similarly, children in homes with ≥2 dogs or cats are less likely to be allergic than those in homes without dogs or cats. 503 Exposure of an infant to the mother's vaginal microflora through vaginal delivery may also be beneficial; the prevalence of asthma is higher in children born by Caesarian section than those born vaginally.…”