Background: Helicobacter pylori is a bacterium that infects the lining of the stomach and intestines. It can cause peptic ulcers, cancers, and infections. Current methods of diagnosing H. pylori infections have limitations. Researchers want to test a new method of testing for H. pylori.

Objective: To compare the esophageal string test (EST) to standard tests for detecting H. pylori infection.

Eligibility: People aged 18 years or older with persistent H. pylori infection.

Design: Participants will have 3 or 4 clinic visits over 2 to 4 months. Screening visit: Participants will have a physical exam. They will provide a stool sample. Baseline visit: Participants will have blood tests. Then they will have the EST: One end of a string will be taped to the outside of their cheek; the other end will be packed into a capsule. Participants will swallow the capsule, and the string will unwind down their throat into their stomach. The string will be left in for at least 1 hour. Then researchers will gently pull out the string. The fluids soaked into the string will be studied. Some participants will be prescribed antibiotics. Follow-up visit 1: Participants whose H. pylori infection was cured by the antibiotics may leave the study. Those who are still infected will have an endoscopy: A flexible tube will be inserted down the throat and into the stomach. It will take tissue samples from the stomach lining. These participants will then receive antibiotics again. Follow-up visit 2: The physical exam, blood test, and stool sample will be repeated. ...