International travel and acquisition of multidrug- resistant Enterobacteriaceae: a systematic review

RJ Hassing 1 2 3 , J Alsma 3 4 , MS Arcilla 5 , PJ van Genderen 6 , BH Stricker 1 7 , A Verbon 4 5 1. Department of Epidemiology, Erasmus University Medical Center, Rotterdam, the Netherlands 2. Department of Internal Medicine, Rijnstate Hospital and Travel Clinic Oost, Arnhem, the Netherlands 3. These authors contributed equally to this article 4. Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, the Netherlands 5. Medical Microbiology and Infectious Diseases, Erasmus University Medical Center, Rotterdam, the Netherlands 6. Institute for Tropical Diseases, Havenziekenhuis, Rotterdam, the Netherlands 7. Inspectorate of Health Care, Utrecht, the Netherlands


Introduction Rationale
Worldwide, the number of international travellers has grown from 25 million in 1950 to 1,087 million in 2013 [1]. According to the World Tourism Organization, this number is expected to increase by an average of 3.3% a year [1]. Of the international travellers visiting developing countries, 22-64% have self-reported health problems and about 8% require medical care during or after travel [2,3]. Healthy travellers may be exposed to a broad range of microorganisms while travelling, including drug-resistant Enterobacteriaceae, which may subsequently be introduced into their home country [4,5].
Enterobacteriaceae are Gram-negative bacteria that are part of the human body's normal commensal flora, called microbiota. Enterobacteriaceae, such as Escherichia coli and Klebsiella species, are capable of causing both healthcare-associated and community-acquired infections [6]. Multidrug-resistant Enterobacteriaceae (MRE), including extended-spectrum beta-lactamase (ESBL)producing Enterobacteriaceae (ESBL-E) and plasmidmediated Amp C-producing Enterobacteriaceae (pAmp C-E) are emerging worldwide [7]. Cases of carbapenemase-producing Enterobacteriaceae (CPE) are also reported more frequently [8].
Since 2003, community carriage rates of MRE have increased dramatically in various regions, such as South-East Asia, the Western Pacific and the Eastern Mediterranean [7]. During visits to such areas, travellers might acquire MRE and become asymptomatic carriers of MRE. In their home country, they may cause spread in the community and contribute to worldwide emerging antimicrobial resistance [6,9,10]. Acquired MRE in the digestive tract are considered apathogenic, however carriage of such Enterobacteriaceae have resulted in clinically relevant infections [8]. International travel has been reported as a risk factor for urinary tract infections caused by ESBL-E [11,12]. The question arises if these observations warrant clinicians being aware of MRE in recently returned otherwise healthy, international travellers who seek medical attention even for unrelated conditions. ESBL: extended-spectrum beta-lactamase.

Objectives
The aim of this systematic review was to determine the effect of international travel on the risk of acquisition of faecal carriage of MRE. A secondary objective was to determine risk factors for acquisition of drug resistance.

Protocol and registration
A specific protocol was designed and used to conduct the study. The study is registered in the international prospective register of systematic reviews (PROSPERO) under registration number CRD42015024973.

Search strategy and selection criteria
The systematic review was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [13]. For inclusion the article needed to fulfil the following criteria [1]: It needed to be related to foreign travel [2], report on screening in asymptomatic participants [3], present antimicrobial susceptibility data and [4] report on faecal Enterobacteriaceae carriage. We used the following exclusion criteria: case reports, reviews, metaanalyses, veterinary medicine, in vitro studies and studies regarding symptomatic patients. The reference lists of reviews were screened to identify studies possibly missed by the search.
Two researchers (R.H. and J.A.) independently performed the screening of the abstracts. Any discordant result was discussed in consensus meetings. After

Box
Search strategy for systematic review of the acquisition of multidrug-resistant Enterobacteriaceae in international travel screening the abstracts, the full text of the articles was assessed for eligibility by the same two researchers and selected or rejected for inclusion in the systematic review. In case of disagreement a third researcher (A.V.) decided on inclusion.

Data collection process
The

Quality assessment
We assessed the methodological quality and the risk of bias in individual studies that may affect the cumulative evidence, using tools for assessing quality and susceptibility to bias in observational studies as recommended in the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement [15,16].

Data synthesis and analysis
As a result of the design of the studies (cohort studies) and the heterogeneity in patient populations (e.g. travellers, healthcare workers and healthcare students), a formal meta-analysis was not possible. Therefore, the study results were summarised to describe the main outcomes of interest. The principle summary measure was percentage of MRE acquisition during travel, defined as ESBL-E or pAmp C-E. Furthermore, risk factors for acquisition of drug resistance were assessed. If possible, percentages not presented in the articles were calculated from the available data.

Study characteristics
Eleven prospective cohort studies, conducted in northern and western Europe, Australia and the United States (US) were included [17][18][19][20][21][22][23][24][25][26][27]. The characteristics of these studies are shown in Table 1. Nine studies investigated travellers visiting a travel or vaccination clinic, one study hospital staff and contacts, and one study healthcare students working or studying abroad. The number of study participants ranged from 28 to 574. The median age of travellers in the individual studies varied between 25 and 66 years, with the youngest group being healthcare students. In all studies, the majority of travellers were female (range: 55-78%). The proportion of participants who were lost to follow up varied from 3.8% (4/106) [18] to 30% (12/40) [21]. The mean duration of travel was similar in all studies (14-21 days). In the study by Angelin et al. on healthcare students, median length of stay was 45 days (range: 13-365 days) [22]. In four studies, follow-up samples of MRE carriers were collected at six months after returning from travel, and in one of these studies, samples were collected monthly in the first three months with further follow-up until 12 months after return [25]. Ten studies used a phenotypic method for susceptibility testing, with genotypic confirmation of ESBL positivity by PCR [17][18][19][20][21][22][24][25][26][27]. One study used a PCR-based approach [23]. In one study, only isolated E. coli were included, whereas the other studies included all isolated Enterobacteriaceae, which mainly consisted of E. coli [17][18][19][20][21][22][23][24][25][26][27].

Acquisition of multidrug-resistant Enterobacteriaceae
Faecal carriage of MRE varied from 1 to 12% before travel and acquisition of MRE from 21% to 51% (  [26]. The risk of acquisition of MRE varied with the geographical region (Table 3) [17][18][19][20][21][23][24][25][26][27]. Travel to southern Asia posed the highest risk (range: 29-88%), followed by other Asian countries (18-67%) and Northern Africa (range: 31-57%). Acquisition of MRE after travelling to sub-Saharan Africa (range: 0-49%) or South and Central America (range: 0-33%) was less frequent, and three studies did not observe any acquisition of MRE after travel to South or Central America ( Table 3). Acquisition of MRE after travel to North America, Europe and Oceania was rare. Results of the genotypic characterisation of MRE isolated after travel are presented in Table 2, the majority of the genes belonged to the CTX-M type.

Risk factors for acquisition of multidrugresistant Enterobacteriaceae
Besides travel destinations, other risk factors for acquiring MRE were age, use of antibiotics during travel (beta-lactam use) and gastroenteritis or other gastrointestinal symptoms ( outcome, showed that travel diarrhoea (adjusted odds ratio (AOR) = 31.0; 95% confidence interval (CI): 2.7-358.1)) and antibiotic therapy for travel diarrhoea (AOR = 3.0; 95% CI: 1.4-6.7) proved to be the most important risk factors for acquiring MRE [20]. In the study of Kuenzli et al. in which only travellers to southern Asia were included, risk factors for MRE acquisition were length of stay, visit to family or friend and consumption of ice cream or pastry (

Duration of multidrug-resistant Enterobacteriaceae carriage after return, risk factors for a long duration and rate of infection after travel
Five studies analysed MRE carriage six months after travel, and the persistence rate of acquired MRE after six months was 6-24% of travellers (

Rate of transmission to household members
Only one study screened household contacts for MRE after return of the index traveller. Household contacts were defined as persons who shared the same household with a participant on a regular basis. Two of 11 contacts were found MRE-positive [24]. Both carried a different ESBL-producing E. coli based on multilocus sequence typing (MLST) than the associated traveller.

Limitations of the studies
The quality of the studies and the susceptibility of bias between the studies were assessed. In all but one study, participants constituted a non-random sample of the general travelling population [17][18][19][20][21][23][24][25][26][27]. However, Angelin et al. studied healthcare students working or studying abroad [22]. Studies were performed on three different continents.
Returning international travellers with MRE may introduce these microorganisms in their home countries. This may cause community-onset infections with MRE in patients without obvious risk factors transmitted by healthy carriers through food or person-to-person contact [9]. Infections caused by MRE are associated with poorer outcome and a higher overall mortality rate than infections caused by susceptible bacteria [28]. In this review, all studies showed an increased prevalence of faecal carriage of ESBL after international travel. It is not possible to evaluate the proportion of travellers who will develop infection with these resistant bacteria. However, studies have demonstrated that international travel is a risk factor associated with developing an infection with an MRE [11,12,29].
Many countries have infection prevention and control guidelines to detect and treat multidrug-resistant organisms (MDROs) including MRE [30]. In countries with low prevalence of MRE, infection prevention and control guidelines mainly include strategies for early identification and isolation of patients recently hospitalised in foreign hospitals [30,31] for MRE seems indicated in such patients. Furthermore, empiric antibiotic therapy may fail when an infection by MRE is not taken into account. Therefore, careful recording of travel history needs to be incorporated in each patient evaluation. As shown in this review, there is also an increased risk of resistance against other antibiotics in travellers with MRE carriage. It is likely that this is caused by multiple genes, each encoding resistance to different classes of antibiotics, which are often found on the same bacterial mobile genetic element (e.g. a plasmid) [32]. As a result, other antibiotics, such as aminoglycosides, will also fail in many MRE-positive patients.
Of all MDROs, emergence of CPE is most worrisome because of the limited treatment options for these infections. NDM-1-producing Enterobacteriaceae have been found in environmental samples in endemic regions [33]. CPE (NDM-1) in patients from the United Kingdom with a recent history of travelling or medical tourism to India are already an important public health problem [8]. Case reports have also demonstrated acquisition of CPE in travellers without contact with medical healthcare facilities [34,35]. In this review, four travellers from India were carrying a carbapenemase-producing E. coli [25,26]. Preliminary results of the Carriage Of Multiresistant Bacteria After Travel (COMBAT) study, a large-scale multicentre longitudinal cohort study conducted in the Netherlands among 2001 travellers, show acquisition of CPE in four travellers [36].
There are, besides the destination of travel, additional risk factors for acquiring MRE during travel. Antibiotic therapy was found to increase the risk [20,22]. In five studies, traveller's diarrhoea or gastroenteritis were associated with an increased risk of MRE acquisition during travel [17][18][19][20]25]. Also, in one study, meticulous hand hygiene or strict consumption of bottled water did not lower the risk of acquiring MRE [22]. Therefore, it is not clear whether hygiene-related travel advice will decrease faecal carriage of MRE. Surprisingly, healthcare-related activities did not pose an increased risk of acquiring MRE in one study [22].
MRE and CPE could also be carried by food. International spread of these bacteria by food supply has been reported [37]. In this review, only one study showed that food consumption (ice cream and pastry) was associated with MRE carriage in travellers to southern Asia, whereas most of the studies did not focus on dietary patterns during travel.
One limitation of this review is the recruitment of travellers from travel clinics only, resulting in inclusion of very few travellers with European destinations. Some European countries such as Greece and Cyprus are also endemic for MRE and popular travel destinations [34]. In addition, travellers visiting their country of origin, especially Morocco and Turkey usually do not ask for a pre-travel consultation, although these countries are endemic for MRE and CPE [34]. It is not clear whether not including these patients may have led to an underor overestimation of MRE acquisition.
Another limitation is the lack of sufficient data regarding the duration of carriage and the transmission among non-travelling household members. The study by Ruppé et al. suggests that three months after return, MRE carriage is comparable with the baseline prevalence before travelling. However, the study did not include baseline prevalence in the follow-up. The COMBAT study will address some of these questions [38].

Conclusion
International travel is a major risk factor for acquisition of MRE. This risk is particularly high after travelling to (southern) Asia and in persons with travel-related diarrhoea and antibiotic use. Carriage of MRE-positive isolates is also associated with a high risk of resistance to ciprofloxacin, cotrimoxazole and aminoglycosides. Further research is needed to assess duration of carriage, spread to household contacts and whether introduction of MRE results in an increase of MRE infections. Our results, combined with the worldwide emergence of CPE, further stress the importance of infection prevention and control guidelines.
to be submitted and any revised version. Annelies Verbon: This author made substantial contributions to conception and design and analysis and interpretation of data; this author participated in revising the article critically for important intellectual content; this authors gave final approval of the version to be submitted and any revised version.