Respiratory atopic disease, Ascaris-immunoglobulin E and tuberculin testing in urban South African children

Background: Epidemiological relation of intestinal helminth infection and atopic disease, both associated with a T-helper (Th) 2 immune response, is controversial, as it has been reported that helminth infection may either suppress or pre-dispose to atopic disease. This relation has not been tested in an area with a high burden of Mycobacterium tuberculosis (MTB) infection, a known Th1-stimulating infection. Objective: To study the association of intestinal helminth infection and atopic disease in a community where helminth infection is endemic and MTB infection is high. Methods: Three-hundred and fifty-nine randomly selected children aged 6-14 years from a poor urban suburb were tested with allergy questionnaire, skin prick test (SPT) to common aeroallergens, Ascaris-specific IgE (Ascaris-sIgE), fecal examination for pathogenic intestinal helminths and tuberculin skin testing (TST). Histamine bronchoprovocation was tested in the group of children aged 10 years and older. Results were corrected for demographic variables, socioeconomic status, parental allergy, environmental tobacco smoke (ETS) exposure in the household, recent anthelminthic treatment and for clustering in the sampling unit. Results: Ascaris-sIgE was elevated in 48% of children, Ascaris eggs were found in 15% and TST was positive in 53%. Children with elevated Ascaris-sIgE had significantly increased risk of positive SPT to aeroallergens, particularly house dust mite, atopic asthma (ever and recent), atopic rhinitis (ever and recent) and increased atopy-related bronchial hyper-responsiveness. In children with negative TST (<10 mm), elevated Ascaris-sIgE was associated with significantly increased risk of atopic symptoms (adjusted odds ratio (ORadj) 6.5; 95% confidence interval (CI) 1.9-22.4), whereas in those with positive TST (≥10 mm) this association disappeared (ORadj 0.96; 95% CI 0.4-2.8). Conclusions: These results suggest that immune response to Ascaris (Ascaris-sIgE) may be a risk factor of atopic disease in populations exposed to mild Ascaris infection and that MTB infection may be protective against this risk, probably by stimulation of anti-inflammatory networks. © 2006 Blackwell Publishing Ltd.