Environmental triggers of nocturnal dry cough in infancy: new insights about chronic domestic exposure to formaldehyde in the PARIS birth cohort.

Although formaldehyde is a common indoor pollutant, its impact on respiratory symptoms in childhood remains unclear. The aim of this study was to examine the relation between domestic formaldehyde exposure and occurrence of coughing, one of the most prevalent respiratory symptoms during the first year of life of infants from the PARIS birth cohort involving 3840 healthy full-term babies. The presence of respiratory symptoms, including dry cough at night apart from a cold or chest infection in the past 12 months was reported on a standardized health questionnaire. Formaldehyde exposure was estimated for all infants using a predictive model established from data (both repeated measurements and information about determinants of levels) collected in a random sample of infants from the cohort. An unconditional logistic regression was fitted to study the relation between annual domestic formaldehyde exposure and dry cough at night, adjusting for all potential risk factors/confounders. The prevalence of dry cough at night was 14.9%. Parental history of allergy was found to modify the relation between environmental factors and dry cough. Cockroaches, used mattresses, and family stressor events were associated with dry cough in infants with parental allergy history. Conversely, domestic formaldehyde exposure tended to increase occurrence of dry cough at night only among babies without parental history of allergy (adjusted OR per 10 µg/m(3) increase in levels, single imputation approach: 1.45, 95% CI: 1.08-1.96, and Bayesian approach: 1.12, 0.91-1.36). This study suggests that the impact of indoor environmental exposure on dry cough at night in infancy is different depending on the presence or not of parental history of allergy.