Past Antibiotic Use Affects Resistance and Outcomes of Helicobacter pylori Infection

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The summary below is from the full report titled "The Relationship among Previous Antimicrobial Use, Antimicrobial Resistance, and Treatment Outcomes for Helicobacter pylori Infections." It is in the 16 September 2003 issue of Annals of Internal Medicine (volume 139, pages 463-469). The authors are B.J. McMahon, T.W. Hennessy, J.M. Bensler, D.L. Bruden, A.J. Parkinson, J.M. Morris, A.L. Reasonover, D.A. Hurlburt, M.G. Bruce, F. Sacco, and J.C. Butler.

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

Helicobacter pylori is a common type of bacteria that usually infects people during their childhoods. In most cases, the infection does not cause problems. However, some people with H. pylori infection get inflammation or ulcers in the stomach or upper intestine. Doctors treat inflammation and ulcers caused by H. pylori with several antibiotics (for example, amoxicillin, clarithromycin, or metronidazole) for several days. Antibiotics get rid of H. pylori in most patients, but 10% to 20% of patients may still have infection despite treatment. Several factors may predispose patients to "antibiotic-resistant" infections. One possible factor is previous use of antibiotics that left behind resistant bacteria.

Why did the researchers do this particular study?

To see if past use of antibiotics affects resistance and treatment outcomes of H. pylori infections.

Who was studied?

125 Alaska Native adults infected with H. pylori. All had endoscopy for symptoms such as heartburn, nausea, or vomiting.

How was the study done?

At endoscopy, doctors removed small amounts of infected tissue from each patient's stomach. They sent the tissue for culture to see if it grew H. pylori and, if it did, tested the H. pylori to see if it was sensitive or resistant to several antibiotics. Then, the doctors treated the infected patients for 2 weeks with 2 to 3 different antibiotics. Patients were given tests (urea breath tests) 2 months after treatment to see if they still had H. pylori infection.

The researchers reviewed outpatient, hospital, and pharmacy records to see which patients had taken antibiotics in the past. The researchers noted any antibiotic use in the 8 to 10 years before endoscopy. They then compared previous use of antibiotics in patients with and without resistant infections.

What did the researchers find?

One third of the H. pylori infections were resistant to clarithromycin (a macrolide antibiotic). Two thirds were resistant to metronidazole. People who had used the same or a similar antibiotic in the past more commonly had infections that were resistant to that antibiotic. People who had taken many previous courses of macrolide antibiotics had greater risk for H. pylori infections that were resistant to clarithromycin than did people who had used those antibiotics less often. Seventy-seven percent of the patients with clarithromycin-resistant H. pylori infection had persistent infections after treatment with drug regimens that included clarithromycin.

What were the limitations of the study?

Alaska Natives have a very high prevalence of H. pylori infections. Findings in this group might differ from those in other patient groups in whom H. pylori infection is less common. Also, past antibiotic use may have been underestimated. The study was based on review of records at the Alaska Native Medical Center, and some persons may have received antibiotics from other places. Only 96 of 125 patients had breath tests to see if infection remained after treatment.

What are the implications of the study?

People who have used antibiotics in the past have increased risks for H. pylori infections that are resistant to those antibiotics. Clarithromycin-containing therapy for H. pylori infection often fails in people who are resistant to clarithromycin.