Latitude Modifies the Effect Size of Factors Related to Recurrent Wheeze in the First Year of Life

Background: Although the association between latitude and asthma prevalence has been studied to a certain extent, its influence on the magnitude of the association of risk/protective factors with recurrent wheeze in infants has never been reported. Methods: The adjusted odd ratios (aOR) of various risk/protective factors for recurrent wheeze from 31 920 infants from 19 centres of the "Estudio Internacional de Sibilacias en Lactantes" (EISL) in very different parts of the world were used to build a meta-regression using the strength of the aOR of each factor as dependent variable and centre latitude as explanatory variable. The meta-regression was further adjusted for continent. Results: There was a positive significant correlation between latitude and the magnitude of the aOR between recurrent wheeze and having cold(s) during the first three months of life (p = 0.004); attending a nursery school (p = 0.011); and having additional siblings (p = 0.003). Furthermore, there was a negative correlation for having been breastfed for at least three months (p = 0.044). Heterogeneity (as measured by I2) of the magnitude of aORs between centres was quite high except for breast feeding: 73.1% for colds; 66.9% for nursery school; 52.6% for additional siblings; and 18.1% for breast feeding. Latitude explained a considerable amount of that heterogeneity: 63.8% for colds; 52.8% for nursery school; 86.6% for additional siblings; and 100% for breast feeding, probably as a consequence of its low heterogeneity. Conclusion: The magnitude in which some risk/protective factors are associated to recurrent wheeze during the first year of life varies significantly with latitude. © 2013 Elsevier Ltd. All rights reserved.