Molecular epidemiological characterization of enterotoxigenic and enteroaggregative Escherichia coli causing traveller’s diarrhoea and their association with persistence of symptoms

BACKGROUND Traveller’s diarrhoea (TD) remains one of the most prevalent health concerns affecting individuals visiting low- to middle-income countries. Among the primary infectious agents, two pathogenic variants of Escherichia coli are especially prominent: enteroaggregative E. coli (EAEC) and enterotoxigenic E. coli (ETEC). However, comprehensive epidemiological data on these pathogens remain limited and often region-specific. This study aimed to characterize EAEC and ETEC isolates collected from international travellers attending the International Health Department at Hospital Clínic, Barcelona, during two periods: 2001–2014 and 2018–2023. METHODS A total of 90 EAEC and 91 ETEC isolates were analysed using Multi-Locus Sequence Typing (MLST) and Whole Genome Sequencing (WGS) to determine their Sequence Types (STs) and Clonal Complexes (CCs). Epidemiological and clinical information was retrospectively collected through medical records. Multivariable logistic regression models were employed to evaluate risk factors associated with persistent diarrhoea. RESULTS Distinct ST distributions were observed between the two pathotypes. ST10 was predominant in EAEC, while ST4 was most common in ETEC; both belonged to CC10. ST10, ST4 and eight additional STs were identified in Latin America, Asia and Africa (international clones), comprising nearly half of all isolates. ST distributions shifted between study periods, indicating dynamic epidemiological patterns. Importantly, infections caused by CC10 strains were significantly associated with an increased risk of persistent diarrhoea (aOR 5.5) and ST10 was associated with longer duration of symptoms (aCoeff 76.5). Other variables, including pathotype, ST4, and in vitro biofilm production, were not associated with prolonged symptoms. CONCLUSIONS These findings underscore the importance of clonal spread in global TD epidemiology, as a substantial portion of isolates belonged to international clones. The changing ST profiles over time highlight evolving transmission patterns. Moreover, the association of ST10/CC10 with persistent diarrhoea suggests that molecular typing may have clinical relevance in predicting disease outcomes and guiding targeted interventions.