Etiology of traveller's diarrhea: Which diarrheagenic Escherichia coli pathotype most commonly causes acute, watery traveller's diarrhea acquired from contaminated food or water in resource-limited settings?

Introduction / Context:
Traveller's diarrhea is a common syndrome among visitors to endemic regions, characterized by sudden-onset, watery stools, cramps, and sometimes low-grade fever. Identifying the predominant etiologic agent informs prevention (food and water hygiene) and empiric therapy decisions.

Given Data / Assumptions:

• Illness is acute and watery rather than dysenteric.
• Exposure is via contaminated food or water while traveling.
• We focus on E. coli pathotypes.

Concept / Approach:
ETEC is the classic cause of traveller's diarrhea. It colonizes the small intestine and produces heat-labile (LT) and/or heat-stable (ST) enterotoxins that stimulate chloride and water secretion, leading to watery diarrhea without prominent invasion or blood. EPEC causes infantile diarrhea; EHEC causes hemorrhagic colitis/HUS; EIEC is invasive and causes dysentery-like illness.

Step-by-Step Solution:
Match clinical pattern (watery, non-bloody) to toxin-mediated disease.Identify ETEC toxins (LT/ST) as key drivers of secretory diarrhea.Exclude invasive or hemorrhagic pathotypes.Select ETEC.

Verification / Alternative check:
Field studies and outbreak investigations consistently implicate ETEC as the leading cause of traveller's diarrhea across continents.

Why Other Options Are Wrong:

• EPEC: classically infantile, attaching/effacing pathology.
• EIEC: invasive with fever and blood/mucus.
• EHEC: bloody diarrhea and risk of HUS; undercooked beef and unpasteurized foods.

Common Pitfalls:
Assuming antibiotics are always required; many cases are self-limited, with oral rehydration as first-line management.

Final Answer:
entero toxigenic E. coli (ETEC)