The correct answer is E. Helicobacter pylori is a small, gram-negative bacterium that lives in and locally destroys the mucus coating that lines the stomach. It is the most common chronic bacterial infection and has been linked to a wide variety of problems, including gastritis, peptic ulcer disease, gastric cancer, and gastric lymphoma. Multiple antibiotic regimens are available for treatment, which are typically accompanied by administration of a proton pump inhibitor (PPI). All patients who are treated for H. pylori infection should be tested to confirm eradication, which necessitates a test which can detect active infection. Noninvasive options are the urea breath test or the stool antigen test.
In the urea breath test, the patient is given oral urea that has been labeled with 13C or 14C. The H. pylori bacteria contain the enzyme urease and are able to metabolize the urea, producing radioactively labeled CO2, which can be measured in breath samples taken 20-30 minutes after ingestion. It is recommended that this test be delayed until four weeks after the end of the regimen, since recent antibiotic use may have decreased the number of organisms enough to produce a negative test, without having achieved true eradication.
Culture of gastric biopsy (choice A) is highly specific but requires both endoscopic biopsy (an invasive test) and fastidious culture technique. Therefore, this method is not often used clinically for follow-up studies.
The rapid urease test (choice B) is also performed on gastric tissue. It is rapid, specific, and sensitive, but requires endoscopy to obtain the biopsy fragment and is therefore an invasive rather than a noninvasive test.
Qualitative assays of antibodies against H. pylori (choice C) may be positive for up to three years after eradication of the infection, and therefore do not detect active infection.
Quantitative assays of antibodies against H. pylori (choice D) drop slowly for up to three years after eradication of the infection.
