INTRODUCTION
Allergic rhinitis (AR) is a common allergic disease in childhood, and its prevalence is increasing worldwide.1-3 AR significantly impacts the quality of life by causing various problems, such as sleep disturbance, emotional stress and impairment of school activities.4 More importantly, AR is a risk factor for asthma as “one airway, one disease”.5-7 The International Study of Asthma and Allergies in Childhood (ISAAC) employed standardized methodology and showed clearly that the prevalence of AR increased during childhood, i.e., from 6-7 y.o. to 13-14 y.o.8
However, the onset of AR in children is not well understood due to the absence of definitive diagnostic criteria. We previously reported that, in school children with asthma, AR started even before 3 years of age.9 In the PARIS birth cohort study, the prevalence of AR-like symptoms was 9.1% at 18 months of age.10However, in the above studies, diagnosis of AR was based only on the parents’ recall in the former and a symptom questionnaire in the latter. In addition, those reports did not provide a good description of the development process.
With the aim of improving our understanding of the onset of AR, we designed and carried out a high-risk infant cohort study, the Impact of Allergic Rhinitis on Atopic March (IRAM) in children. Infants less than 2 years of age who had food allergy or atopic dermatitis were recruited into the study. We prospectively followed up not only their nasal symptoms, but also their nasal cytology and allergic sensitization for 2 years. The ARIA guidelines classify AR as intermittent or persistent, not seasonal or perennial.11 However, Japan is characterized by sole high morbidity of seasonal AR due to Japanese cedar pollen and a high prevalence of perennial AR due to house dust mite (HDM). Accordingly, the Japanese guidelines include classifications for seasonal AR and perennial AR.12 Here, in light of the relatively late development of pollen sensitization in young children,13 we focused on development of HDM-sensitized perennial AR in infancy.