antibiotics

Antibiotic Resistance to Traveler’s Diarrhea Treatment Is Spreading Across the Globe

A new study examined resistance patterns for common causes of acute diarrhea and found that the two main types of antibiotics used to treat this condition are becoming less effective among international travelers in sub-Saharan Africa and Latin America.

Antimicrobial resistance (AMR) is a global health crisis, fueled in part by human misuse of antibiotics. A new study by a School of Public Health researcher examined AMR to antibiotics used to treat traveler’s diarrhea (TD) and found widespread patterns of resistance among international travelers, which varied by region of travel.

Published in JAMA Network Open, the study found an increase in AMR to both fluoriquinolones and macrolides, the two main types of antibiotics that clinicians prescribe to treat the most common bacterial causes of TD, with fluoroquinolones receiving the widest resistance across geographic regions. AMR to this particular class of antibiotics has been common in South and Southeast Asia for more than a decade, but the new findings show that this resistance has since expanded to sub-Saharan Africa and South America.

Based on these results, macrolide antibiotics are the most effective antibiotic for infected travelers who are diagnosed with TD in any region, except for those diagnosed with the Shigella species in South America, where fluoroquinolones are more effective. 

“Moderate to severe TD can disrupt vacation, business travel, and visits with friends and family,” says study co-senior author Davidson Hamer, professor of global health and medicine at BUSPH and BU Chobanian & Avedisian School of Medicine. “With the progressive loss of fluoroquinolones, the only remaining treatment option for most cases of TD is azithromycin—a macrolide sold under brand names such as Z-Pak and Zithromax—and our data suggest that resistance to this macrolide is also starting to rise.

“If resistance to azithromycin rises, we will have almost no good, relatively inexpensive option available for treatment of TD,” Hamer says.

The lead author of the study is Bhawana Amatya of the CIWEC Hospital and Travel Medicine Center in Kathmandu, Nepal. The other co-senior authors are Daniel Leung of the University of Utah School of Medicine, and Bradley A. Connor of Weill Cornell Medical College and the New York Center for Travel and Tropical Medicine.

Typically caused by consuming contaminated food or water, TD affects up to 88 percent of international travelers around the world, with symptoms that include loose stools, vomiting, stomach cramps, and fever. The majority of cases resolve with hydration and time, but more severe infections—characterized by bloody stools, high fever, and sharp abdominal or rectal pain—may require antibiotics for treatment. 

Understanding the geographical and pathogenic patterns of AMR to these medications can help travelers and clinicians make appropriate decisions in treating this unpleasant gastrointestinal condition while minimizing the potential for increased AMR. Tracking the geographic patterns of AMR to TD medications can also guide treatment of severe TD cases in regions that are unable to identify specific bacterial strains and determine the effectiveness of antibiotics through lab-based antimicrobial susceptibility testing (AST), due to limited resources.

Hamer says international travelers should also adhere to guidelines developed by a group of travel medicine experts in 2017, which advise judicious use of TD antibiotics, including limiting treatment to just one day, if possible, for moderate-to-severe cases.

For the study, Hamer and colleagues analyzed AMR patterns for the four main bacterial pathogens that cause TD: Campylobacter species, nontyphoidal Salmonella (NTS) species, Shigella species, and Escherichia coli (E. coli) among 859 international travelers identified by the GeoSentinel Surveillance Network with a culture-confirmed case of traveler-associated diarrhea between April 2015 and December 2022.

The increase in resistance to diarrheal infections caused by the Shigella bacteria, particularly in South America, was especially concerning to the researchers. Shigella pathogens can damage the intestinal lining leading to inflammation and bleeding, so they usually require antibiotic treatment, Hamer says. Importantly, Shigella TD can be transmitted person-to-person through the fecal-oral route, by touching contaminated surfaces or food, or sexual activity. The researchers recommend that certain groups who are infected with this strain, such as men who have sex with men, people with young children, and those who handle food, consider antibiotic treatment, and infected individuals who are hospitalized should even consider third-generation cephalosporins, or antibiotics prescribed under brand names such as ceftriaxone and cefdinir.

“Ideally, travelers from high-income countries such as the US and Canada, should have a pretravel consultation with a travel medicine specialist, if possible—or as a backup, their primary care provider—before traveling to low- and middle-income countries [LMICs] where the risk of TD is moderate to high,” says Hamer.

The researchers stress that AST results for TD cases should be obtained whenever possible to inform the most appropriate treatment plan.

“We definitely need improved global surveillance systems for tracking antibiotic susceptibility to common diarrheal pathogens, as well as a number of bacteria responsible for bloodstream infections that can be much more serious and potentially life-threatening, such as typhoid fever, and hospital-acquired bloodstream infections,” Hamer says, acknowledging that LMICs have limited capacity to store or test TD cultures. “Funding for strengthening microbiological capacity and resistance surveillance is needed. In the meantime, surveillance networks such as the GeoSentinel, which uses returning travelers, immigrants, and refugees to track infectious diseases and antimicrobial resistance, help provide important data on the global extent of AMR.”