Allergic sensitization and respiratory infection in infancy-Too early for two-hits on lung function?

Allergic sensitization and respiratory infections are common in childhood. The "two-hit" hypothesis suggests these interact in early-life to increase risk of subsequent asthma. The "two-hit" effect on lung function, however, remains unknown.

We assessed for interactions between food allergic sensitization and respiratory infection in infancy and associations with lung function in childhood.

In a longitudinal community-based cohort, sensitization was assessed at age 1 year by skin prick testing to common food allergens. Respiratory infection was assessed via parental reports of doctor diagnosed bronchiolitis or antibiotics for lower respiratory infection in the first year of life. Regression models were fitted with interactions between these exposures to assess for associations with lung function at ages 6 and 10 years, controlling for potential confounders.

No interaction was observed between food sensitization and lower respiratory infection in infancy on lung function at either age 6 or 10 years. Respiratory infection was associated with modest reductions in lung function at age 10 years for post-bronchodilator FEV₁ in both sensitized (-0.25, 95% CI: -0.55 to 0.05 z-score units, p = .108, n = 285) and non-sensitized (-0.12, 95% CI: -0.26 to 0.02 z-score units, p = .081, n = 1179) children. Similar patterns were observed for FEV₁/FVC, FVC, and FEF_25-75. Associations were weaker and less consistent at age 6 years.

A two-hit interaction between food sensitization and respiratory infection during infancy on subsequent lung function was not confirmed. Early-life lower respiratory infection was however associated with modest reductions in lung function at age 10 years, regardless of sensitization status.