709IS THERE CAUSAL RELATIONSHIP BETWEEN HELICOBACTER PYLORI AND DUODENAL ULCER? A REVIEW STUDYBackground: Helicobacter pylori (H. pylori) is spiral-shaped bacteria that can cause peptic ulcer disease by damaging the mucous coating that protects the lining of the stomach and duodenum. A peptic ulcer is a sore on the inner lining of the stomach or duodenum. Causes of peptic ulcer disease includes; H. pylori, NSAIDs, cancerous or noncancerous tumors. The design of the study, therefore, was to assess causal relationship between H. pylori and duodenal ulcer (DU).Methods: A systematic search of the literature was conducted to identify relevant studies using the following databases: MEDLINE, PsycINFO, EMBASE and CINAHL. The literature search included 19 published articles from inception of each database to May 8, 2019. A combination of key terms and/or subject headings was applied, between H. pylori terms (H. pylori*, Helicobacter pylori*), and peptic ulcer, duodenal ulcer, gastric ulcer. Titles and abstracts of all articles retrieved using the search criteria defined above were screened independently by two authors, full text screening was then performed to identify studies to be included in the present review. Results: There is strong evidence that H. pylori is an important causal factor in duodenal ulcer formation and relapse. However, there is no direct evidence in humans that H. pylori infection precedes the development of duodenal ulcer; duodenal ulcers have been absent in human volunteers and animal models infected with H. pylori. Moreover, Koch's postulates for a causal link between H. pylori and duodenal ulcer are not fulfilled. However, H. pylori is the cause of active chronic antral gastritis, which is a well-recognized risk factor for duodenal ulcer. Conclusions: The published evidence does not establish H. pylori as a cause of duodenal ulcer, it is not sufficient H. pyloric alone to cause duodenum ulcer, gastric acid is need as well. isayasafewerki2050@gmail.comResearch1012020 H. pylori, duodenum ulcer, causal-relationship, NSAIDs, infection.Isayas Afewerki Abraham,Zewdi Amanuel Dagnew,Yemane Fessehaye Berhe,R. Aroun PrasathIsayas Afewerki Abraham,Zewdi Amanuel Dagnew,Yemane Fessehaye Berhe,R. Aroun Prasath