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Introduction: Little is known about the role of H pylori in human atherosclerosis. We have previously demonstrated its presence in carotid plaques, especially among asymptomatic patients, with prevalence of cagA-positive strains. Polymorphisms of genes of angiotensin-converting enzyme (ACE), lipoprotein APOE (APOE), IL1 receptor antagonist (IL1Ra) and myeloperoxidase (MPO) are associated with atherosclerosis. We evaluated the role of H pylori in certain features of carotid plaques and assessed allelic and genotypic frequencies and their association with H pylori infection and plaque characteristics.Methods: We studied 137 carotid plaques of patients undergoing endarterectomy. We categorized as stable those predominantly fibrous plaques with scarce inflammatory cells, intact cap and no hemorrhage and unstable those plaques with inflammation, thin cap, ruptured lipid core, thrombi and hemorrhage. We extracted genomic DNA and identified and typified H Pylori DNA. DNA was also obtained from peripheral blood and we identified allelic and genotypic frequencies and susceptibility variants of ACE, APOE, IL1Ra, and MPO genes. Fisher’s exact test (two-tailed) and good fit test were used.Results: There were 72 asymptomatic patients with 47 stable and 25 unstable plaques and 65 symptomatic patients with 13 stable and 52 unstable plaques (p<0.0001). H pylori infection was present in 48 of 60 stable plaques and 31 of 77 unstable plaques (p<0.0001). In addition, stable infected plaques more often carried the more virulent cagA strain. H pylori cagA-negative plaques had larger intima media complex thickness than cagA-positive and H pylori-negative plaques. Stable infected plaques were associated to alleles APOE-33 and IL1RN-11. Unstable noninfected plaques were associated to proatherogenic alleles ACE-DD, APOE*4, APOE*2, IL1RN*2, and MPO-GG.Conclusions: Histopathological features of plaque instability are associated to the presence of recent symptoms. H pylori infection with the virulent cagA strain is highly prevalent in stable carotid plaques of asymptomatic subjects. Noninflammatory genotypes are present in stable infected plaques whereas proatherogenic polymorphisms are predominant in unstable noninfected plaques.