Background: In children, the prevalence of allergy increases with increasing socioeconomic status. If frequent immune response stimulation by infections protects against development of allergic diseases, then a social gradient in infections should exist. The aim of our study was to assess the relation between social class, immune parameters, and the prevalence of respiratory infections in children.
Methods: A cross-sectional survey examined children aged 5 to 14 years in 3 communities of Sachsen-Anhalt, Germany. Data of 1724 children were gathered by a parent-completed questionnaire and analyses of blood samples. Social class was defined by parental educational level. Immune parameters included serum immunoglobulin (Ig)G, IgA, and IgM; the C3c component of complement; and the total leukocyte count. The period prevalence of febrile colds and lifetime prevalences of physician-diagnosed bronchitis, tonsillitis, otitis media, and pneumonia were assessed from parents' reports. Adjusted odds ratios for the association between social class and belonging to the group of children with immune parameter levels in the upper 50th or 75th percentile or experiencing respiratory infections were calculated by logistic regression.
Results: Social class was inversely associated with secondary immune response parameters (IgG, IgA), whereas indicators of primary immune reactions and inflammation (IgM, C3c, leukocytes) were not related to social status. While an inverse social gradient was found for the period prevalence of febrile colds, the frequency of bronchitis, tonsillitis, and otitis media decreased with decreasing social class.
Conclusions: Health inequalities exist in immune reactions and respiratory infections in children from different social classes. We hypothesize that in children from lower social classes, increased frequency of infections stimulated the secondary immune response and protected against more severe courses of respiratory infections.