ORIGINAL ARTICLE Effects of Helicobacter pylori, geohelminth infection and selected commensal bacteria on the risk of allergic disease and sensitization in 3-year-old Ethiopian children A. Amberbir 1,2 , G. Medhin 3 , W. Erku 3 , A. Alem 4 , R. Simms 5 , K. Robinson 6 , A. Fogarty 2,5 , J. Britton 2,5 , A. Venn 2,5 and G. Davey 1 1 School of Public Health, Addis Ababa University, Addis Ababa, Ethiopia, 2 Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK, 3 Aklilu Lemma Institute of Pathobiology, Addis Ababa University, Addis Ababa, Ethiopia, 4 Department of Psychiatry, Addis Ababa University, Addis Ababa, Ethiopia, 5 Respiratory Biomedical Research Unit, University of Nottingham, Nottingham, UK and 6 Centre for Biomolecular Sciences, University of Nottingham, Nottingham, UK Clinical & Experimental Allergy Correspondence: Alemayehu Amberbir, Division of Epidemiology and Public Health, University of Nottingham, Clinical Sciences Building, Hucknall Road, City Hospital, Nottingham NG5 1PB, UK. E-mail: alamwo1@yahoo.com Cite this as: A. Amberbir, G. Medhin, W. Erku, A. Alem, R. Simms, K. Robinson, A. Fogarty, J. Britton, A. Venn , and G. Davey, Clinical & Experimental Allergy , 2011 (41) 1422–1430. Summary Background Epidemiological studies have suggested that gastro-intestinal infections including Helicobacter pylori, intestinal microflora (commensal bacteria) and geohelminths may influence the risk of asthma and allergy but data from early life are lacking. Objective We aimed to determine the independent effects of these infections on allergic disease symptoms and sensitization in an Ethiopian birth cohort. Methods In 2008/09, 878 children (87% of the 1006 original singletons in a population-based birth cohort) were followed up at age 3 and interview data obtained on allergic symptoms and potential confounders. Allergen skin tests to Dermatophagoides pteronyssinus and cockroach were performed, levels of Der p 1 and Bla g 1 in the child’s bedding measured and stool samples analysed for geohelminths and, in a random subsample, enterococci, lactobacilli, bifidobacteria and H. pylori antigen. The independent effects of each exposure on wheeze, eczema, hayfever and sensitization were determined using multiple logistic regression. Results Children were commonly infected with H. pylori (41%; 253/616), enterococci (38.1%; 207/544), lactobacilli (31.1%; 169/544) and bifidobacteria (18.9%; 103/544) whereas geohelminths were only found in 8.5% (75/866). H. pylori infection was associated with a borderline significant reduced risk of eczema (adjusted OR 0.49, 95% CI 0.24–1.01, P = 0.05) and D. pteronyssinus sensitization (adjusted OR 0.42, 95% CI 0.17–1.08, P = 0.07). Geohelminths and intestinal microflora were not significantly associated with any of the outcomes measured. Conclusion and Clinical Relevance Among young children in a developing country, we found evidence to support the hypothesis of a protective effect of H. pylori infection on the risk of allergic disease. Further investigation of the mechanism of this effect is therefore of potential therapeutic and preventive value. Keywords eczema, geohelminths, Helicobacter pylori, microflora, sensitization Submitted 16 February 2011; revised 20 June 2011; accepted 22 June 2011 Introduction It is estimated that around 300 million people in the world have asthma and that it accounts for 1 in 250 deaths world- wide [1]. Epidemiological studies have shown a rise in the prevalence of symptoms of asthma and associated allergic conditions in many countries [1, 2], and there is consistent evidence that adoption of a western lifestyle and increased urbanization are associated with increased risk of allergic diseases [1–3]. One hypothesis that has attracted much recent interest is that organisms living in the gut, which become less prevalent with increased urbanization and better hygiene, may play a protective role in the aetiology of asthma and allergy. In tropical areas, the first exposure to gastro-intestinal infections such as parasites typically oc- curs at an early age, during a crucial period of immune development, however, to date, most studies have been based on older children or adult populations [4, 5]. Particular interest has focused on the protective role of the stomach-colonizing bacterium Helicobacter pylori. Epidemiology of Allergic Disease  EC doi: 10.1111/j.1365-2222.2011.03831.x Clinical & Experimental Allergy, 41, 1422–1430  c 2011 Blackwell Publishing Ltd