Abstract
BackgroundThe association between atopy and asthma is attenuated in non-affluent populations, an effect that may be explained by childhood infections such as geohelminths.ObjectiveTo investigate the association between atopy and wheeze in schoolchildren living in urban and rural areas of Ecuador and examine the effects of geohelminths on this association.MethodsWe performed nested case–control studies among comparable populations of schoolchildren living in rural communities and urban neighbourhoods in the Province of Esmeraldas, Ecuador. We detected geohelminths in stool samples, measured recent wheeze and environmental exposures by parental questionnaire, and atopy by specific IgE (sIgE) and skin prick test (SPT) reactivity to aeroallergens.ResultsAtopy, particularly sIgE to house dust mite (HDM), was more strongly associated with recent wheeze in urban than rural schoolchildren: (urban, adj. OR 5.19, 95% CI 3.37–8.00, P < 0.0001; rural, adj. OR 1.81, 95%CI 1.09–2.99, P = 0.02; interaction, P < 0.001). The population fractions of wheeze attributable to atopy were approximately two-fold greater in urban schoolchildren: SPT to any allergen (urban 23.5% vs. rural 10.1%), SPT to HDM (urban 18.5% vs. rural 9.6%), and anti-HDM IgE (urban 26.5% vs. rural 10.5%), while anti-Ascaris IgE was related to wheeze in a high proportion of rural (49.7%) and urban (35.4%) children. The association between atopy and recent wheeze was attenuated by markers of geohelminth infections.ConclusionsOur data suggest that urban residence modifies the association between HDM atopy and recent wheeze, and this effect is explained partly by geohelminth infections.
Highlights
Atopy is a consistently strong risk factor for asthma in industrialized countries [1, 2], but this association appears to be weaker [3,4,5,6] in non-industrialized countries
We included subjects for whom complete data were available for wheeze and allergen-specific IgE from both case–control studies: 149 cases and 227 controls in the rural and 104 cases and 120 controls in the urban case– control study
Recent anthelmintic treatment was associated with an increased risk of wheeze in both studies this was only significant in the rural area (P = 0.01)
Summary
Atopy is a consistently strong risk factor for asthma in industrialized countries [1, 2], but this association appears to be weaker [3,4,5,6] in non-industrialized countries. The association between atopy and allergic disease appears to be stronger in affluent compared to nonaffluent [6] and in urban compared to rural populations [10, 11]. Urban–rural differences in the prevalence of environmental exposures that attenuate atopy could explain these observations. Geohelminth infections, that are common chronic parasitic infections of predominantly low-income rural populations in the tropics, may have a role in attenuating the association between atopy and allergic symptoms [16] including wheeze [17, 18]
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