"Stomach Flu" Is Not Caused by Influenza Virus
"Stomach flu" is a misleading colloquial term for viral gastroenteritis, which has no biological association with influenza viruses. The term is commonly used to describe the illness because low-grade fever and body aches can accompany the gastrointestinal symptoms, but the causative agents are entirely different viruses that specifically target the gastrointestinal tract 1.
Primary Viral Causes of "Stomach Flu"
The viruses that actually cause what people call "stomach flu" include:
Most Common Pathogens
Norovirus is the leading cause of epidemic viral gastroenteritis in people of all ages, with GII.4 strains associated with the majority of outbreaks worldwide since 2001 1
Rotavirus is the most common cause of severe diarrhea in children under 5 years of age, infecting virtually every child by age 4 years and causing potentially lethal dehydration in 0.75% of children less than 2 years old 1
Adenoviruses (particularly serotypes 40 and 41) contribute to 5%-20% of hospitalizations for childhood diarrhea in developed countries, with peak incidence among children less than 2 years of age 1
Caliciviruses (including sapovirus) account for approximately 3% of children hospitalized for diarrhea, with most people acquiring antibodies by age 12 1, 2
Astrovirus is another important etiologic agent of acute gastroenteritis, particularly in children 3, 4
Clinical Distinction from Influenza
Symptom Profile
- Viral gastroenteritis presents with acute onset nonbloody diarrhea, vomiting, nausea, and abdominal cramps as primary symptoms 1
- Incubation periods vary: 12-48 hours for norovirus, 1-3 days for rotavirus and calicivirus 1, 2
- Illness typically resolves in 1-3 days for most patients, though children, elderly, and hospitalized patients may experience 4-6 day courses 1
Why the Confusion Exists
- The term "stomach flu" persists because low-grade fever and body aches can accompany gastrointestinal symptoms, superficially resembling influenza 1
- However, true influenza is a respiratory illness caused by influenza A or B viruses, not gastrointestinal viruses 1
Important Clinical Caveat
Healthcare providers should avoid reinforcing the "stomach flu" terminology with patients, as it perpetuates confusion about influenza vaccination and disease prevention strategies. Influenza vaccines protect against respiratory influenza viruses but provide no protection against the gastrointestinal viruses that cause viral gastroenteritis 1.