Do early-life allergic sensitization and respiratory infection interact to increase asthma risk?

Abstract

Objective

The ‘two-hit’ hypothesis theorizes that early life allergic sensitization and respiratory infection interact to increase asthma risk.

Methods

We sought to determine in a high allergy risk birth cohort whether interactions between early life allergic sensitization and respiratory infection were associated with increased risk for asthma at ages 6–7 years and 18 years. Allergic sensitization was assessed at 6, 12, and 24 months by skin prick testing to 3 food and 3 aeroallergens. Respiratory infection was defined as reported “cough, rattle, or wheeze” and assessed 4-weekly for 15 months, at 18 months, and age 2 years. Regression analysis was undertaken with parent-reported asthma at age 6–7 years and doctor diagnosed asthma at 18 years as distinct outcomes. Interactions between allergic sensitization and respiratory infection were explored with adjustment made for potential confounders.

Results

Odds of asthma were higher in sensitized compared to nonsensitized children at age 6–7 years (OR = 14.46; 95% CI 3.99–52.4), There was no evidence for interactions between allergic sensitization and early life respiratory infection, with a greater frequency of respiratory infection up to 2 years of age associated with increased odds for asthma at age 6–7 years in both sensitized (OR = 1.13; 95% CI 1.02–1.25, n = 199) and nonsensitized children (OR = 1.31; 1.11–1.53, n = 211) (p interaction = 0.089). At age 18 years, these associations were weaker.

Conclusions

Our findings do not support ‘two-hit’ interactions between early life allergic sensitization and respiratory infection on asthma risk. Both early life respiratory infections and allergic sensitization were risk factors and children with either should be monitored closely for development of asthma.

Keywords:

• Allergic sensitization
• asthma
• viral respiratory infection
• interaction
• cohort study

Disclosure statement

The authors have no conflicts of interest to report.

Additional information

Funding

MJA holds investigator-initiated grants from Pfizer, Boehringer-Ingelheim, Sanofi and GlaxoSmithKline for unrelated research. He has also undertaken an unrelated consultancy for Sanofi and received a speaker’s fee from GSK.