Effect of urban vs. rural residence on the association between atopy and wheeze in Latin America: findings from a case-control analysis.
BACKGROUND
The association between atopy and asthma is attenuated in non-affluent populations, an effect that may be explained by childhood infections such as geohelminths.


OBJECTIVE
To 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.


METHODS
We 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.


RESULTS
Atopy, 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.


CONCLUSIONS
Our data suggest that urban residence modifies the association between HDM atopy and recent wheeze, and this effect is explained partly by geohelminth infections.
['Endara|P|P|', 'Vaca|M|M|', 'Platts-Mills|T A E|TA|', 'Workman|L|L|', 'Chico|M E|ME|', 'Barreto|M L|ML|', 'Rodrigues|L C|LC|', 'Cooper|P J|PJ|']
D000293:Adolescent D000485:Allergens D000818:Animals D016022:Case-Control Studies D002648:Child D003430:Cross-Sectional Studies D004781:Environmental Exposure D005260:Female D006801:Humans D006969:Hypersensitivity, Immediate D007073:Immunoglobulin E D007843:Latin America D008297:Male D012135:Respiratory Sounds D012307:Risk Factors D012424:Rural Population D012882:Skin Tests D011795:Surveys and Questionnaires D014505:Urban Population D055815:Young Adult
urban rural atopy wheeze Latin America geohelminths house dust mite tropics