Causes of Traveller's Diarrhea
Bacterial pathogens account for 80–90% of traveller's diarrhea cases, with enterotoxigenic and enteroaggregative Escherichia coli (ETEC and EAEC) being the most common culprits, followed by Campylobacter, Shigella, and non-typhoidal Salmonella species. 1
Primary Bacterial Etiologies
The bacterial causes dominate the landscape of traveller's diarrhea:
Enterotoxigenic E. coli (ETEC) and enteroaggregative E. coli (EAEC) are globally the most frequent pathogens causing traveller's diarrhea, with EAEC detected in approximately 40% of cases and ETEC in 34% of cases. 2
Enteropathogenic E. coli (EPEC) represents another significant pathotype, found in approximately 32% of travelers and significantly associated with symptomatic diarrhea. 2
Campylobacter species are common bacterial causes, particularly in certain geographic regions where they demonstrate high rates of antimicrobial resistance. 1, 3
Shigella species and non-typhoidal Salmonella species round out the major bacterial pathogens responsible for traveller's diarrhea. 1, 3
Enterotoxigenic Bacteroides fragilis has emerged as a newly identified agent causing traveller's diarrhea, though less common than the traditional pathogens. 4
Geographic Variation in Etiology
The specific causative organisms vary significantly by destination:
South Asia carries the highest risk for diarrheal syndromes among returned travelers, followed by sub-Saharan Africa and South America. 4
In Southeast Asia, Campylobacter demonstrates fluoroquinolone resistance exceeding 90%, making it a particularly challenging pathogen in this region. 5
Regional resistance patterns significantly influence which pathogens predominate and which antibiotics remain effective. 1
Less Common Etiologies
While bacteria dominate, other pathogens contribute to a minority of cases:
Parasites and viruses are less common causes of traveller's diarrhea compared to bacterial pathogens. 6
Protozoan parasites (Giardia, Cryptosporidium, Cyclospora) should be considered when diarrhea persists for ≥14 days. 5
In multiplex PCR testing, protozoan parasites were not detected in acute traveller's diarrhea cases, emphasizing their limited role in typical presentations. 2
Clinical Context and Pathogen Detection
Understanding pathogen detection requires clinical correlation:
Multiplex PCR panels may detect multiple enteric pathogens, but only diarrheagenic E. coli (particularly EPEC and ETEC) show significant association with symptomatic traveller's diarrhea. 2
Positive PCR results may reflect non-viable organisms; confirmatory culture is advised when antimicrobial susceptibility could influence therapy. 5
Asymptomatic travelers may test positive for enteric pathogens (57% in one study), highlighting that detection does not always equal causation. 2
Critical Risk Factors
Several factors influence both acquisition and etiology:
Travel destination is the most significant risk factor, with developing countries posing the highest risk. 6
Duration of stay correlates with increased risk, particularly among long-term travelers and deployed military personnel who show 30% self-reported incidence. 3
Female gender is associated with increased susceptibility to travel-related diarrhea. 4
Type of accommodation influences risk, with hotel stays associated with higher rates compared to other lodging types. 7