# When Influenza Masquerades as Gastroenteritis: Acute Diarrhea in an Adult With Influenza B

## TL;DR

A case report shows that influenza B can present with diarrhea instead of typical respiratory symptoms, leading to misdiagnosis.

## Contribution

Highlights the atypical presentation of influenza B as acute diarrhea, emphasizing the need for broader diagnostic consideration.

## Key findings

- Influenza B presented with acute watery diarrhea and fever in a 46-year-old male without initial respiratory symptoms.
- Misdiagnosis as gastroenteritis occurred before confirming influenza B via rapid antigen testing.
- Timely antiviral treatment with oseltamivir led to full recovery.

## Abstract

Influenza is a common viral respiratory illness caused by influenza A and B viruses, typically presenting with fever, cough, sore throat, myalgia, and malaise. Gastrointestinal symptoms are less common, particularly in adults, but may occasionally predominate. Diarrhea as the initial manifestation of influenza is rare and may mimic acute gastroenteritis, leading to diagnostic delay and inappropriate therapy.

This is a case report of a 46-year-old male with influenza B presenting primarily with acute watery diarrhea and fever, without initial respiratory symptoms. The atypical presentation initially led to a misdiagnosis of acute gastroenteritis. Confirmation of influenza B was obtained via rapid antigen testing, and the patient was successfully treated with oseltamivir, achieving full recovery.

This case underscores the importance of considering influenza in the differential diagnosis of febrile diarrheal illness, especially during seasonal epidemics and in travelers. Recognition of such atypical presentations enables early laboratory confirmation and timely antiviral therapy, preventing unnecessary antibiotic use, and contributes to improved clinical and public health outcomes.