An antibiotic called rifaximin may help prevent traveler's diarrhea caused by E. coli bacteria, according to a new study.

That may be particularly helpful in Mexico, where E. coli accounts for most cases of traveler's diarrhea, say the researchers in the Annals of Internal Medicine.

However, rifaximin hasn't been proven to treat traveler's diarrhea that is not caused by E. coli, and it didn't completely prevent the problem, in the study by Herbert DuPont, MD, and colleagues.

Traveler's diarrhea is the most common illness affecting travelers, says the CDC. Diarrhea strikes 20 percent-50 percent of international travelers (an estimated 10 million people) every year.

Diarrhea Prevention Test

The FDA approved rifaximin last summer to treat traveler's diarrhea caused by E. coli. DuPont's team tested the antibiotic on American students who were new in Mexico and had not yet developed traveler's diarrhea.

DuPont's study included 210 healthy adults who were taking summer classes and living with local families in Guadalajara, Mexico. The students got instruction on avoiding traveler's diarrhea, including safe food selection. They ate most of their meals in local homes with local families; however, the researchers expected similar rates of diarrhea as if their meals were consumed in public restaurants.

They also took rifaximin or a placebo during their first two weeks in Mexico; they didn't know which pills they had received.

Participants were followed for three weeks to see if diarrhea developed and for two more weeks to track side effects. While the students took their treatment, changes in the normal bacteria of the gut were tracked. Antibiotic treatment changes the normal gut environment and can lead to antibiotic-resistant bacteria.

Fewer Diarrhea Cases With Rifaximin

The rifaximin group had fewer cases of diarrhea during their first two weeks in Mexico. Of the students taking rifaximin, nearly 15 percent developed diarrhea compared with more than half of the students that took the placebo.

Rifaximin provided 72 percent protection against traveler's diarrhea. All rifaximin doses fared better than the placebo, the study shows.

The rifaximin group also got protection from milder diarrhea and moderate-to-severe intestinal symptoms such as pain, cramps, and excessive gas. Minimal effects were seen on intestinal flora.

Rifaximin and the placebo had comparable rates of side effects (such as headache and sore throat), write researchers.

The Right Strategy?

Rifaximin appears to be an "ideal drug" for preventing bacterial diarrhea "and should be safe even for prolonged use in at-risk international travelers," writes DuPont, who works at the University of Texas Health Science Center at Houston.

However, a journal editorial questions the appropriateness of prescribing an antibiotic to millions of travelers every year.

"Rapid and judicious treatment of diarrhea, not antibiotic prophylaxis, is the best recommendation for most travelers," writes Sherwood Gorbach, MD, of Tufts University's medical school.

Upcoming Studies

DuPont and colleagues say they're planning studies in Asia, where bacteria including shigella, salmonella, and campylobacter are common causes of traveler's diarrhea.

They also want to find out if rifaximin helps prevent post-infectious irritable bowel syndrome. The two-week study wasn't long enough to test that, the researchers say.

Avoiding Traveler's Diarrhea

Traveler's diarrhea is mainly caused by infections from fecally contaminated food and water, says the CDC. Choosing foods and beverages carefully while overseas may help avoid those bugs.
The CDC offers these tips on preventing traveler's diarrhea:

— Avoid eating foods or drinking beverages purchased from street vendors or other establishments where unhygienic conditions are present.
— Avoid eating raw or undercooked meat and seafood.
— Avoid eating raw fruits (such as oranges, bananas, and avocados) and vegetables unless the traveler peels them.
— Tap water, ice, unpasteurized milk, and dairy products are associated with increased risk for traveler's diarrhea.
— Well-cooked and packaged foods — if handled properly — are usually safe.
— Safe beverages include bottled carbonated beverages, hot tea or coffee, beer, wine, and water that's been boiled or appropriately treated with iodine or chlorine.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: DuPont, H. Annals of Internal Medicine, May 17, 2005; vol 142: pp 805-812. Gorbach, S. Annals of Internal Medicine, May 17, 2005; vol 142: pp 861-862. News release, CDC. CDC: "Traveler's Diarrhea: Frequently Asked Questions."