Detection of Persistent Helicobacter pylori Infection

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The summary below is from the full report titled "The Stool Antigen Test for Detection of Helicobacter pylori after Eradication Therapy." It is in the 19 February 2002 issue of Annals of Internal Medicine (volume 136, pages 280-287). The authors are D Vaira, N Vakil, M Menegatti, B van't Hoff, C Ricci, L Gatta, G Gasbarrini, M Quina, JM Pajares Garcia, A van der Ende, R van der Hulst, M Anti, C Duarte, JP Gisbert, M Miglioli, and G Tytgat.

What is the problem and what is known about it so far?

Helicobacter pylori (H. pylori) is a common type of bacteria that people usually get infected with during childhood. In most cases, the infection does not cause symptoms. However, some people with H. pylori infection eventually develop inflammation of the stomach (gastritis) or ulcers in the stomach or upper small intestine. Gastritis and ulcers cause abdominal pain and, sometimes, bleeding. Doctors often treat gastritis and ulcers caused by H. pylori with a combination of several antibiotics that are given for several days. Treatment gets rid of H. pylori in most patients, but 10% to 20% of patients may have persistent infection despite treatment. Continuing abdominal pain does not reliably identify patients with persistent H. pylori infection because there are other reasons why people can have continued pain. Ideally, a simple noninvasive test could be used to identify patients who do not respond to traditional treatment and who need additional treatment. One proposed test is a stool test (called the stool antigen test). The accuracy of this test has not been well studied.

Why did the researchers do this particular study?

To see whether the stool antigen test correctly identifies people with persistent H. pylori infection despite treatment.

Who was studied?

The researchers studied 84 patients who had had endoscopy (a test in which a tube is used to view the stomach and take samples of it for biopsy). All of the patients had upper abdominal pain and positive biopsy or culture for H. pylori.

How was the study done?

Patients were treated with a combination of antibiotics for 7 to 10 days. Stool collections for the stool antigen test were done multiple times after therapy was completed (3, 7, 15, 21, 28, and 35 days later). A second endoscopy with repeated cultures and biopsies was done 35 days after treatment. The researchers then compared the findings of the stool antigen tests with the findings from the repeated endoscopy to see whether the stool antigen test accurately identified people with persistent H. pylori infection.

What did the researchers find?

Seventeen patients had persistent H. pylori infection. Stool antigen tests done immediately after completion of antibiotic treatment (within 3 days) did not accurately identify patients with persistent infection. However, stool antigen tests done 7 or more days after completion of antibiotic treatment did identify patients with persistent infection. Positive stool antigen tests at day 7 or later correctly identified patients with persistent infection about 95% (range, 70% to 100%) of the time. Negative stool antigen tests at day 7 or later correctly identified patients without persistent infection about 90% (range, 80% to 100%) of the time.

What were the limitations of the study?

Because the study was small, the researchers could not precisely measure the accuracy of the stool antigen test. Thus, the range of probabilities given above was wide.

What are the implications of the study?

Stool antigen tests done relatively soon after completion of antibiotic therapy (7 days or later) that have a positive result correctly identify most patients with persistent H. pylori infection.