Tummy trouble: The most common bacteria in the world

By Allen Hwang, MD, Tufts Medical Center


The most common bacterial infection in humans is caused by an organism called Helicobacter pylori (H. pylori). H. pylori causes an infection of the lining of the stomach and small intestines. More than 50 percent of the world’s population harbors this bacterium. While the rate of infection in the United States is lower than the world average, immigrants from Asian countries such as China, Japan, Korea, Malaysia, Singapore, Taiwan and Vietnam can have rates of infection as high as 80 percent.

The infection is usually acquired early in life, and without treatment, is persistent. Chronic infection can lead to a number of different complications. H. pylori is the leading cause of stomach and small intestinal ulcers. Even more worrisome, it is the leading cause of stomach cancer, the second most common cancer in the world. It can also cause intestinal lymphoma, a white blood cell cancer.

While it has yet to be determined how H. pylori is transmitted, research shows that it is likely transmitted through exposure to the saliva or feces of those who are infected. The infection usually affects many members of a household, suggesting person-to-person transmission.

Most people who are infected with H. pylori have no symptoms. However, in some patients, it can cause a number of symptoms, including:

1) Pain in the upper belly

2) Bloating

3) Feeling full after only small amounts of food

4) Lack of appetite

5) Nausea and vomiting

6) Dark or black-colored bowel movements

7) Fatigue

People with those symptoms should seek medical attention to see if testing for H. pylori is recommended. A number of tests are available to make the diagnosis, including blood and stool tests. Your physician may also recommend an upper endoscopy if there is a possibility of ulcers or cancer.

Fortunately, there are good treatment regimens for H. pylori that consist of three to four medications taken simultaneously for two weeks. They are easily tolerated and very effective. Eradication of the bacteria improves healing of ulcers, if present, and decreases the risk of stomach cancer and white blood cell cancers of the intestines.

If you have any questions about H. pylori, you can schedule an appointment with Doctor Hwang by calling (617) 636-5883.


Allen Hwang, MD, is double-board certified in internal medicine and gastroenterology. He is an assistant professor of medicine at Tufts Medical Center in the division of gastroenterology.

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