international travel

A recently published study in The Lancet investigates the acquisition and spread of resistant bacteria ESBL-E among international travellers.


Superbugs. They flash across news headlines and have been the subject of many sci-fi movies. We often sensationalize them, but how big of a threat do they actually pose to the public?

“Superbugs” is a common term often referred to microbes that develop antimicrobial resistance. Antimicrobial resistance is the ability of microbes, such as bacteria, viruses and parasites, to resist the effects of a medication previously used to treat them. When they are exposed to antimicrobial drugs, these microbes change, allowing them to survive and continue multiplying to cause more harm. These resistant microbes have become a serious threat to global public health. They are able to develop new mechanisms of resistance, further threatening our ability to treat and prevent common infectious diseases. This problem escalates when resistant microbes spread internationally. And with international tourism escalating to one billion travellers in 2014, the problem of antimicrobial resistance demands the action of all government sectors and society.

Recent studies have shown that international travel allows the fast transport of resistant microbes and plasmids between regions. Plasmids are circular bacterial DNA that hold sites for genes that code for resistance. Certain plasmids may code for extended-spectrum beta-lactamase enzymes. These enzymes inactivate antibiotics by opening the beta-lactam ring on antibiotics. When they open the beta-lactam ring, the enzymes deactivate the molecule’s antibacterial properties. Extended-spectrum beta-lactamase producing Enterobacteriaceae (ESBL-E) are bacteria that produce these enzymes, and are thus typically resistant to multiple classes of antibiotics. This is a problem as it leaves us with few to no effective antimicrobial agents to prevent and treat infectious diseases.

Previous studies have looked at the acquisition of ESBL-E among international travellers, but there has been little data on ESBL-E colonization after travel. Researchers questioned: what are the factors that may predict the acquisition of ESBL-E by travellers? What is the probability of ESBL-E transmission to others within a household?

Finding the answers to these questions will help us establish the public health risk of the introduction and spread of antimicrobial resistance by travellers. It would also help us find the measures needed to monitor or manage the risks of spread via international travel. And these are the questions that scientists in the Netherlands recently sought to answer.

international travel

In a study recently published in The Lancet, the scientists investigated the acquisition of ESBL-E during international travel, focusing on the predictive factors for the acquisition of ESBL-E, the duration of its colonization in individuals, and the probability of it being transmitted to others within a household.

For this study, researchers recruited a total of 2001 Dutch travellers and 215 non-travelling household members from three outpatient travel clinics across the Netherlands from November 2012 to November 2013. The median age of these adult participants was 50 years and most were in good health before travelling. The main purpose for their travel was tourism and the median travel duration was 20 days. These participants most frequently visited the sub-regions of Southeast Asia, southern Asia, eastern Africa, and South America.

The investigators provided the participants with feces collection kits and instructed them to self-collect fecal swabs before and immediately one month after their travel. If the researchers found ESBL-E in the samples, the traveller and their household members had to provide further samples at three, six, and 12 months after travel. If researchers did not find ESBL-E in the samples, then the participants did not need to provide any additional samples. The participants also had to answer questionnaires at all time points. These questionnaires allowed investigators to collect information on potential risk factors for ESBL-E acquisition, including demographics, illnesses, and behaviour before, during and after travel.

The study found that approximately 34% of travellers acquired ESBL-E during international travel, most being those who travelled to southern Asia. These travellers had been ESBL-E negative prior to travelling. They also found that 11% of participants sustained carrying ESBL-E 12 months after return, and the probability of transmitting it to another household member was 12%.

The strongest independent predictor for acquiring ESBL-E was antibiotic use during travel, but they also found strong links between acquiring ESBL-E and traveller’s diarrhea. Further, they noticed that travellers who ate food from street vendors were at an increased risk of acquiring ESBL-E, and the risk increased even further in travellers who ate from street vendors daily. Another predictor for ESBL-E acquisition during travel was self-reported pre-existing chronic bowel disease.

Based on the results, the researchers suggest that “travellers to areas with a high risk of ESBL-E acquisition should be viewed as potential carriers of ESBL-E for up to 12 months after return.” To reduce the import of ESBL-E by travellers, the authors of the study suggest advising travellers to refrain from using antibiotics to treat self-limiting infections.

However, it is important to note that the frequency of acquiring ESBL-E may differ by destination. For example, travellers to Asia may have acquired ESBL-E at a significantly higher frequency than other regions because of the widespread dissemination of ESBL-E already present in these regions, along with the high risk of food contamination.

Overall, the findings of this study support the fact that international travel facilitates the spread of antimicrobial resistance. And since 320 million people visit Asia, northern Africa, and the Middle East annually, the authors expect international travel to considerably contribute to the spread of ESBL-E in travellers’ home countries. However, the authors do note that “the degree of consequence of the emergence and spread of antimicrobial resistance by travellers differs by region, and is highly dependent on local prevalence of antimicrobial resistance in the country of origin.”


Written By: Jessica Gelar, HBSc

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