**Question:** An 18-month old developed acute gastroenteritis with fever and watery diarrhea that lasted 10 days. She had been vaccinated against rotavirus at 2 and 4 months of age as recommended. Eight days later, both of her brothers, ages 3 and 6, developed acute gastroenteritis. Which of the following tests would most likely reveal the etiologic agent of their gastroenteritis?

A. Stool culture
B. Stool antigen test
C. Serological test
D. Stool viral panel

**Core Concept:**

Acute gastroenteritis is a condition characterized by sudden onset of abdominal pain, vomiting, and diarrhea. In this case, the patient developed gastroenteritis due to rotavirus infection, which is a common cause of viral gastroenteritis in children. Vaccination against rotavirus is recommended during infancy to prevent infection.

**Why the Correct Answer is D:**

The correct answer is Stool viral panel (option D) since it is a comprehensive test that detects various viral pathogens causing gastroenteritis including rotavirus. Vaccination of the 18-month old against rotavirus may have provided some immunity but not complete protection. Testing both brothers' stool samples with the stool viral panel would reveal the etiologic agent of their gastroenteritis.

**Why Other Options are Incorrect:**

A. Stool culture (option A) is useful for detecting bacterial pathogens but would not detect viral infections like rotavirus, which is the most likely cause in this case.

B. Stool antigen test (option B) is designed to detect specific viral antigens but does not cover all viruses causing gastroenteritis, including rotavirus.

C. Serological test (option C) is used to detect antibodies or antigens in the blood but is not suitable for diagnosing gastroenteritis directly.

**Clinical Pearl:**

Diagnosing viral gastroenteritis often requires comprehensive testing like a stool viral panel, especially when the initial infection has been treated or the patient has been vaccinated against the common pathogen. This highlights the importance of considering other causes, such as rotavirus, and the need for appropriate testing to identify the etiologic agent responsible for the gastroenteritis in this case.