This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
All of the following are true about Helicobacter pylori except: 
Select and explain. 
A. About 50% of world population affected, B. 85% of population is affected, in some developing countries, C. All children in developing countries have immunity by five years of age, D. Infection is common in low socio-economic status
C: All children in developing countries have immunity by five years of age
Answer: C: All children in developing countries have immunity by five years of age 
Explanation: Ans. is 'c' i.e., All children in developing countries have immunity by five years of age(Ref: Harrison, 16th/e, p. 886,19th/e, p. 1038; Ananthanarayan, 9th/e, p. 400)* Duodenal ulcer (80%) and Gastric ulcer (60%) are associated with H. pylori.* Gastric adenocarcinoma, gastric MALT lymphoma, Autoimmune gastritis, Hyperacidity.* Chronic gastritis in adults due to the reinfection and Treatment prevents the gastric lymphoma.* Approximately 50% of world population and 85% of developing countries are affected by H. pylori.