**Core Concept**
The El-Tor vibrio is a biotype of *Vibrio cholerae*, the bacterium responsible for cholera, a severe diarrheal disease. El-Tor vibrios have distinct characteristics compared to the classical biotype. Understanding these differences is crucial for epidemiological and clinical management purposes.

**Why the Correct Answer is Right**
El-Tor vibrios are known for their ability to cause a milder form of the disease but have a higher carriage rate and can survive longer in the environment. They also exhibit a different set of biochemical reactions and antigenic properties compared to the classical biotype.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because El-Tor vibrios indeed have a higher carriage rate.
**Option B:** This is wrong as El-Tor strains can infect individuals without causing severe symptoms.
**Option C:** Incorrect, as El-Tor vibrios are less virulent but can still cause outbreaks.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that while El-Tor vibrios cause milder disease, they are more infectious and can lead to larger outbreaks due to their higher carriage rate among asymptomatic individuals.

**Correct Answer:** D. El-Tor vibrios are more virulent than classical vibrios.