2.1 | Study population and clinical data
We enrolled 150 infants and young children (88 boys, 62 girls) aged under 2 years with AD visiting our hospital, Samsung Medical Center, who were living in the Seoul Metropolitan Area of Korea. Locations of their residences are shown in Figure 1. AD was diagnosed according to the Hanifin and Rajka criteria.16 They were followed up until they were 3 or 4 years old.
At enrollment, demographic data were obtained, including date of birth, age of AD onset, and body mass index (BMI). AD severity was assessed using the SCORing Atopic Dermatitis (SCORAD) index, developed by the European Task Force Group on AD in 1993.17 Subjects were classified into three groups, ‘mild (< 25)’, ‘moderate (25−49)’, and ‘severe (≥ 50)’, according to SCORAD at enrollment. Levels of total IgE and specific IgE against egg white, cow’s milk, soybean, wheat and peanut in the peripheral blood were measured using ImmunoCAP (ThermoFisher Scientific Inc., Waltham, MA, USA) and considered positive when levels were 0.69 kU/L or above.
To evaluate the status of AD, AD children were brought to the hospital at least once a year until the age of 3 years. AD remission was defined as absence of AD symptoms in the past 6 months without needing medical treatments including topical corticosteroid (TCS).
When they visited the hospital at age 3, skin prick tests were performed to detect specific IgE against common inhalant allergens includingDermatophagoides pteronyssinus , D. farinae , tree pollen mixture, grass pollen mixture, weed pollen mixture, and cat and dog dander (Lofarma, Milan, Italy). Histamine was used as a positive control, and normal saline was used as a negative control. A positive response to allergens in the skin prick test was determined when wheal size was ≥ 3 mm with adequate reactions to controls.
Written informed consent was obtained from the parent or guardian of each participating child. Study protocols were reviewed and approved by the Institutional Review Board (IRB) of Samsung Medical Center (IRB No. 2014-07-064).