**Question:** A 20-year-old male had pain in abdomen and mild fever followed by gastroenteritis. The stool examination showed the presence of pus cells and RBCs on microscopy. The etiological agent responsible is most likely to be

A. Salmonella
B. Shigella
C. Vibrio
D. Campylobacter

**Correct Answer:** D. Campylobacter

**Core Concept:**
Gastroenteritis is a condition characterized by inflammation of the stomach and intestines, typically caused by bacterial or viral infections. These infections can lead to various symptoms like abdominal pain, fever, and diarrhea. Stool examination is a crucial tool to identify the causative agent.

**Why the Correct Answer is Right:**
The correct answer, Campylobacter, is a bacterial genus known to cause gastroenteritis, particularly in the form of campylobacteriosis. The presence of pus cells and RBCs in the stool indicates severe inflammation, which is commonly seen in campylobacter infections.

**Why Each Wrong Option is Incorrect:**
A. Salmonella: Salmonellosis typically presents with bloody diarrhea, abdominal pain, and fever. Stool examination may show RBCs, but the absence of pus cells makes Salmonella less likely.
B. Shigella: Shigellosis usually presents with bloody diarrhea, abdominal pain, and fever. Stool examination may show RBCs, but the absence of pus cells makes Shigella less likely.
C. Vibrio: Vibriosis is uncommon in causing gastroenteritis and might present with different clinical features. Stool examination may show RBCs, but the absence of pus cells makes Vibrio less likely.
D. Campylobacter: As mentioned earlier, pus cells are indicative of severe inflammation, which is often seen in campylobacter infections.

**Clinical Pearl:**
Campylobacter is a group of bacteria that can cause gastroenteritis, commonly referred to as campylobacteriosis. The presence of pus cells in the stool examination supports the diagnosis of campylobacter infection. While other options like Salmonella, Shigella, and Vibrio can also cause gastroenteritis, the absence of pus cells in the stool examination makes them less likely. The correct answer, Campylobacter, is more likely to present with severe inflammation (pus cells in stool) and is a common cause of campylobacteriosis.