[Incidence of wheezing and associated risk factors in the first 6 months of life of a cohort in Valencia (Spain)]

Objectives: To determine the incidence of wheezing at 6 months of life in the town of Alzira (Valencia, Spain), and to analyse associated risk factors.

Methods: We included 636 newborns in a longitudinal birth cohort study between March 2007 and November 2008. Data were collected from hospital and primary care medical records and from questionnaires sent at 6 months post-natal. Bivariate and multivariate Cox regression analysis were performed to examine the risk factors associated with wheezing.

Results: At 6 months, 25.2% of infants had had 1 or more episodes of wheezing, whereas 5.6% had had 3 or more episodes. Emergency visits were reported in 11.6% of the infants, treatment with oral corticosteroids in 6.6% and admission to hospital in 4%. Independent risk factors for wheezing were male sex (relative risk [RR]: 2.1, 95% confidence interval [95% CI]: 1.5 to 2.9), younger gestational age (RR: 1.1, 95% CI: 1.0 to 1.2), season of birth between July and September (RR: 3.5, 95% CI: 2.0 to 5.9) and between October and December (RR: 2.0, 95% CI: 1.1 to 3.6), younger maternal age (RR: 1.0, 95% CI: 1.0 to 1.1), having siblings (RR: 3.1, 95% CI: 2.2 to 4.5), exposure to smoke (RR: 1.4, 95% CI: 12.0 to 2.0) and history of maternal asthma (RR: 1.7, 95% CI: 1.0 to 3.0). Breast feeding for at least 3 months (RR: 0.6, 95% CI: 0.4 to 0.8) and having immigrant parents (RR: 0.6, 95% CI: 0.4 to 0.9) were protective against wheezing.

Conclusion: A high cumulative incidence of wheezing in the first 6 months of life was found in our population, in comparison with data reported in other cohort studies. Estimated risk factors were generally in accordance with those described by other authors. Having siblings and season of birth between July and September were the most important risk factors, reflecting the role of viral infections in the pathogenesis of wheezing in early childhood.