Can Influenza Cause Gastrointestinal Upset?
Yes, influenza can cause gastrointestinal symptoms, though they occur less frequently than respiratory symptoms and vary by viral subtype. 1, 2
Prevalence of GI Symptoms in Influenza
The occurrence of gastrointestinal upset with influenza is well-documented but varies considerably:
Overall prevalence: A meta-analysis found the pooled prevalence of any digestive symptoms ranged from 30.9% for A(H1N1)pdm09 to 2.8% for seasonal A(H1N1), demonstrating substantial variation between influenza strains 1
Influenza B: Gastrointestinal symptoms such as nausea, epigastralgia (stomach pain), and diarrhea are more prominent with influenza B compared to influenza A subtypes 2
Influenza A subtypes: While A(H3N2) causes more severe systemic illness with higher fever, GI symptoms are less characteristic of this subtype compared to influenza B 2
Clinical Presentation
When GI symptoms occur with influenza, they typically include:
Important caveat: The hallmark presentation of influenza remains abrupt onset of fever, cough, chills or sweats, myalgias, and malaise—respiratory symptoms dominate the clinical picture 3. GI symptoms, when present, are usually accompanying features rather than isolated manifestations.
Viral Detection in Stool
Influenza viral RNA has been detected in stool samples with a pooled prevalence of 20.6%, suggesting the virus can reach the gastrointestinal tract 1
The mechanism likely involves hematogenous dissemination to organs via infected lymphocytes, though direct intestinal infection remains under investigation 1
Recent evidence with A(H5N1) strains demonstrates that influenza A viruses can replicate in mammalian GI tissues and that gastric exposure represents a potential non-respiratory route for infection 4
Clinical Implications
When evaluating patients with GI symptoms during influenza season:
Consider influenza in the differential diagnosis, particularly if respiratory symptoms are also present or develop subsequently 1
Influenza B should be suspected when GI symptoms are prominent, especially in younger patients 2
The diagnosis remains primarily clinical in outpatient settings; laboratory confirmation is not necessary for most patients 3
If testing is pursued and the patient presents within 48 hours of symptom onset, rapid molecular assays are preferred for their accuracy and speed 3
Treatment considerations: Anti-influenza drugs may be considered if started within 48 hours of symptom onset (ideally within 24 hours), as they decrease illness duration by approximately 24 hours and may reduce complications 3