Abstract
Background: The influence of latitude on the strength of the association of risk/protective factors of recurrent wheeze (RW) has never been reported.
Methods: The “Estudio Internacional de Sibilancias en Lactantes” (EISL) included 30,093 infants 12 to 15 months of age, recruited from 13 Latin American centres (n=25,030) and from 5 European centres (n=5,063). Adjusted odd ratios (aOR) of factors associated to RW reported previously were used to build a meta-regression between the strength of the aORs of each factor and centre latitude (distance from equator either N or S). The meta-regression was further adjusted for continent and the slope expressed as adjusted regression coefficient (aRC).
Results: We found significant correlations between latitude (the higher the distance from equator the higher the strength of the association) and the magnitude of the aOR between RW and: 1. Cold(s) in the 1st 3 months (aRC +0.19; p=0.004); 2. Nursery school (aRC +0.25; p=0.01); 3. Siblings (aRC +0.024 per additional sibling; p=0.002); and 4. Breast feeding >=3 months: the higher the latitude the higher the protection (aRC -0.17; p=0.047). Heterogeneity of the strength of aORs between centres was: 73.9% for colds, 67.1% for nursery school, 59.7% for siblings and 22.4% for breast feeding. Latitude explained (by R-squared) much of heterogeneity: 66.1% for colds, 54.9% for nursery school; 83.1% for siblings and 100% for breast feeding.
Conclusion: The magnitude in which some risk or protective factors are associated to recurrent wheeze during the first year of life varies significantly with latitude.
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