title: Helicobacter pylori infection and gastric cancer: systematic review of the epidemiological studies.
abstract: BACKGROUND
  The published epidemiological studies of chronic Helicobacter pylori infection and gastric cancer yield conflicting results, so there is uncertainty as to whether any material association exists and, if so, how strong it is.
  
  
  OBJECTIVE
  To review these studies quantitatively.
  
  
  METHODS
  A systematic review of sero-epidemiological studies published before 1998 of H. pylori and gastric cancer, as identified by computer-assisted literature searches of relevant journals, reference lists and discussions with authors. All relevant studies identified were included, subdivided by study design. The following was abstracted from published reports: adjusted odds ratio (or, in prospective studies, the risk ratio) and confidence interval, study design, type of controls, mean age, mean duration of follow-up, assay methods, location of study, and degree of adjustment for confounders.
  
  
  RESULTS
  The 34 retrospective studies included in total 3300 gastric cancers, but their controls were of uncertain validity. The 10 'nested' case-control comparisons in prospective studies included in total only 800 gastric cancers, and combined analysis of them yielded a risk ratio of 2.5 (95% CI: 1.9-3.4; 2P < 0.00001) for gastric cancer in people seropositive for H. pylori antibodies.
  
  
  CONCLUSIONS
  The prospective studies suggest that gastric cancer is 2 or 3 times as common in those chronically infected by H. pylori, but to help investigate causality, further observational studies are still needed, as are large-scale randomized trials of whether antibacterial regimens reduce the eventual incidence of gastric cancer.
authors.affiliation: Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Medicine, University of Oxford, Radcliffe Infirmary, Oxford, UK. john.danesh@balliol.ox.ac.uk
authors.forename: J
authors.initials: J
authors.lastname: Danesh
mesh_terms: D016021:Epidemiologic Studies; D016481:Helicobacter Infections / Q000150:complications* / Q000453:epidemiology* / Q000382:microbiology; D016480:Helicobacter pylori; D006801:Humans; D016017:Odds Ratio; D011446:Prospective Studies; D012189:Retrospective Studies; D016036:Seroepidemiologic Studies; D013274:Stomach Neoplasms / Q000453:epidemiology* / Q000382:microbiology*