## **Core Concept**
Traveller's diarrhoea is a condition characterized by the sudden onset of loose stools during or shortly after travel, often due to consuming contaminated food or water. The primary causative agents are usually bacterial pathogens. **Escherichia coli** is a leading cause, particularly Enterotoxigenic E. coli (ETEC).

## **Why the Correct Answer is Right**
The correct answer, **Enterotoxigenic E. coli (ETEC)**, is a major cause of traveller's diarrhoea. ETEC produces heat-labile and heat-stable toxins that lead to increased secretion of chloride and bicarbonate into the intestinal lumen, causing watery diarrhoea. This bacterium is commonly found in contaminated food and water, making travellers highly susceptible.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While certain strains of **Shigella** can cause diarrhoea, they are more commonly associated with dysentery, characterized by bloody stools and fever, rather than typical traveller's diarrhoea.
- **Option B:** **Salmonella** can cause gastroenteritis leading to diarrhoea, but it is not the most common cause of traveller's diarrhoea. It often causes more severe symptoms, including fever and abdominal cramps.
- **Option D:** **Vibrio cholerae** causes cholera, a severe diarrhoeal disease usually associated with contaminated water. While it can cause traveller's diarrhoea, it is less common compared to ETEC and typically leads to a more severe, life-threatening condition.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the risk of traveller's diarrhoea can be reduced by following proper food and water safety precautions. The use of prophylactic antibiotics and vaccines (like the Dukoral vaccine for cholera) may also be considered for high-risk travellers. Remember, **"Boil it, cook it, peel it, or forget it"** to minimize risk.

## **Correct Answer:** . Enterotoxigenic E. coli (ETEC).