P2-197 Case-control analysis of the effects of age and geohelminth infection on wheeze and atopy in the rural tropics

Abstract

Background: Epidemiological data suggest that a minority of asthma cases in Latin America may be associated with allergic sensitisation. This fact could be explained by the presence of distinct asthma phenotypes or by the attenuation of atopy or Th2-mediated allergic responses by environmental factors including chronic helminth infections. The aim of the present study was to explore the relationship between levels of IgE specific for allergens (asIgE), skin prick test responses (SPT) and recent wheeze and the effect of age and geohelminth infections on these associations. Method: A case-control study nested within a cross-sectional survey was conducted among 376 children (149 cases and 227 controls) aged 7-19 years living in Afro-Ecuadorian rural communities in Esmeraldas province in Ecuador. Asthma cases were selected based on the presence of recent wheeze and controls as a random sample of those without symptoms by questionnaire. Atopy was measured either by the presence of asIgE in serum or by SPT responses to house dust mite and cockroach. Geohelminth infection was determined by both eggs in stools and anti- Ascaris IgE in serum. Result: Only 30.3% of children (7- 11 years) with asthma in our study population had evidence of some marker of atopy whereas in adolescents (12-19 years) this proportion increased to 48.3%. There was a significant positive association between the markers of atopy (both SPT and asIgE ≥ 3.50 kU/l) and recent wheeze in the older but not in the younger age group. A positive association between anti-Ascaris IgE and wheeze was observed in both the younger (adj.OR 2.06, 95% CI 1.05-4.03) and the older age groups (adj. OR 3.00, 95% CI 1.37-6.56). Having SPT responses to allergens was significantly associated with wheeze among children with no evidence of active geohelminth infection (adj. OR 3.52, 95% CI 1.05-11.79), while this association was lost among children with active infection (adj. OR 1.59, 95% CI 0.72-3.54). The association between SPT and wheeze was not significantly altered by IgE sensitization to Ascaris. Conclusion: Most asthma cases in our population were not attributable to atopy. However, the association between markers of atopy and wheeze increased with age. IgE sensitization to Ascaris, but not active infection was a risk factor for wheeze. The results also suggest modification of the relationship between SPT and wheeze by active geohelminth infection.