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Association of wheeze during the first 18 months of life with indoor nitrogen dioxide, formaldehyde, and family history of asthma: a prospective cohort study.

The trend of childhood hospital admissions for asthma has increased in Hong Kong.1 There is limited evidence of the effect of environmental risk factors on the development of childhood asthma. Environmental exposure to formaldehyde and nitrogen dioxide (NO2) may increase the risk of childhood asthma. Most studies using a case control or cross sectional study design have shown limited epidemiological evidence of the correct temporal relationship between exposures and asthma, and most have not properly examined the role played by family history of asthma or allergy (confounding vs. effect modification). A prospective cohort design would allow proper examination of the temporal relationship between indoor exposure to air pollutants and incident wheezing or asthma. This study aimed to examine: (1) whether exposure to NO2 and formaldehyde at home will increase the risk of new onset wheezing in the first 18 months of life; (2) if there is any exposure-response relationship between NO2 or formaldehyde concentrations and the risk of new onset wheezing; and (3) if the relationship(s) is/are modified by a family history of asthma.