Travelers visiting South Asia were most likely to contract resistant intestinal bacteria.
Not only that, but travelers could also be spreading drug-resistant bacteria to their own countries, contributing the growing problem of antimicrobial resistance.
According to the Centers for Disease Control and Prevention (CDC), travelers' diarrhea is the most common illness to affect travelers. An estimated 10 million people - 20-50% of international travelers - develop the condition, usually occurring within the first week of travel.
In most instances, the use of antibiotics is unnecessary. "The great majority of all cases of travelers' diarrhea are mild and resolve on their own," states lead study author Dr. Anu Kantele.
The authors report that every year, around 300 million travelers visit regions where antimicrobial resistance is a growing risk. Of these travelers, more than 20% return to their home countries colonized by resistant intestinal bacteria.
Bacteria from the Enterobacteriaceae family can produce a particular enzyme in the gut called extended-spectrum beta-lactamase (ESBL). This enzyme is known to promote resistance to several frequently-used antibiotics.
Measuring colonization from ESBL-producing bacteria
The CDC state that ESBLs can be difficult to detect because they act in different ways to different forms of antibiotics. Bacteria that produce ESBLs are capable of causing dangerous infections that are harder and more costly to treat than many other infections.
For the study, published in Clinical Infectious Diseases, the authors analyzed stool samples from 430 Finns before and after traveling outside of Scandinavia for more than four nights to see how many contracted ESBL-producing bacteria while on their travels.
Participants were also asked to complete two questionnaires. The first, a pre-travel survey regarding personal information, medical history and a travel itinerary. Upon returning, the travelers filled out the second questionnaire, concerning their trip and including questions about possible symptoms and medication taken.
The researchers found that 21% of the participants contracted ESBL-producing bacteria while traveling. Risk factors identified for colonization were the region the participants traveled to, age, occurrence of travelers' diarrhea and use of antibiotics for the treatment of diarrhea.
Among participants taking antibiotics to treat their diarrhea, 37% became colonized. Among travelers visiting the riskiest region for resistant bacteria contraction - South Asia - 80% of those taking antibiotics for diarrhea contracted ESBL-producing bacteria.
Rate of colonization is 'serious'
None of the 90 travelers that were colonized by the bacteria went on to develop infections as a result, though the risk of the bacteria spreading from the travelers was still present. Dr. Kantele believes that a larger sample of colonized travelers would probably have yielded infection cases.
"More than 300 million people visit these high-risk regions every year," she states. "If approximately 20% of them are colonized with the bugs, these are really huge numbers. This is a serious thing. The only positive thing is that the colonization is usually transient, lasting for around half a year."
Although the study was the largest on this subject to date, the sample size was still small for travelers visiting a number of regions, including East Asia, North Africa and the Middle East. Data acquired from the study were also observational and, therefore, further research will be needed to determine causation.
For now, the authors write that the best strategies for avoiding colonization from ESBL-producing bacteria is by preventing travelers' diarrhea and restricting the use of antibiotics to treat the condition. "If travelers were instructed to be more cautious in their use of antimicrobials, the number of colonized individuals could decrease dramatically," they conclude.
The authors of a related editorial, also published in Clinical Infectious Diseases, suggest that future studies should investigate the effect of travel on the gut microbiome, measures to prevent travelers' diarrhea and what criteria should inform the use of antibiotics for severe cases.
Recently, Medical News Today reported on the discovery of a new class of antibiotic that could signal the end of drug-resistant superbugs.