Objective: To compare the diameters of Bacille Calmette-Guerin (BCG) scars between asthmatic (allergic) students and normal students, and to compare the diameters of BCG scars in children in rural Beijing area with those in urban Beijing area, and to compare the prevalence of asthmatic (allergic) symptoms and atopy between rural and urban Beijing students.
Methods: Sampled by cluster-random Method, 819 urban school children and 1 044 rural school children aged 13 - 14 years were recruited for the Beijing arm of the phase III international study of asthma and allergies in childhood. The children answered the core questionnaires, and underwent skin prick test for 13 allergens, and were checked for BCG scars on their arms.
Results: (1) In both rural and urban Beijing students, the mean diameters of BCG scars in those with asthma (allergy) (asthma ever, wheeze ever, current wheeze within 12 months, hay fever ever, repeated rash ever, eczema ever, allergic rhinitis, atopy, high-sensitivity or were diagnosed asthma) were (7.0 +/- 2.1) mm-(8.8 +/- 2.8) mm, which were not significantly different from those of (7.2 +/- 2.7) mm-(8.2 +/- 2.2) mm in normal students (P > 0.05). (2) Compared to the urban students, the mean diameter of BCG scars in the rural students was (8.2 +/- 2.3) mm, significantly larger than that of (7.3 +/- 2.9) mm in the urban students (P < 0.01). The prevalence of asthma (allergy) (asthma ever, wheeze ever, current wheeze within 12 months, hay fever ever, repeated rash ever, eczema ever, allergic rhinitis, atopy, high-sensitivity or diagnosed asthma) were 0.6% - 11.4% in the rural Beijing students, significantly lower than that of 3.1% - 35.7% in urban Beijing schoolchildren (P < 0.01).
Conclusions: The diameters of BCG scars were not significantly different between asthmatic (allergic) students and normal students. The diameters of BCG scars in the rural students were significantly larger than those in the urban students. The prevalence of asthma and allergy in the rural children were significantly lower than that in the urban students. The results suggest that there is difference in immunity between rural and urban children from early life, which may be caused by the different living environments.