Stomach Flu: What It Is, Symptoms in Adults, and How It Spreads

"Stomach flu" usually refers to viral gastroenteritis — an infection of the stomach and intestines caused by viruses, not by the influenza virus. In adults it most often presents with sudden vomiting and diarrhea and in most cases resolves within a few days.

What stomach flu is and why it is called that

Viral gastroenteritis is an infection of the stomach and intestines caused by a virus; it is sometimes called "stomach flu." The name is misleading: influenza pathogens have nothing to do with it, and "stomach flu" is a common label, not a diagnosis. In English, the same condition is called stomach flu.

What causes stomach flu

The most common viral pathogens are norovirus, rotavirus, astrovirus, and enteric adenovirus. Norovirus is the most common cause of diarrhea in adults; rotavirus is the leading cause of gastroenteritis in children and occurs less often in adults due to acquired immunity. COVID-19 can also cause symptoms of stomach flu, even without respiratory problems. Less commonly, the cause is bacteria — Escherichia coli, Campylobacter, Salmonella, Shigella.

Symptoms of stomach flu in adults

Symptoms usually appear 4–48 hours after contact with the virus. Common manifestations are abdominal pain, diarrhea, nausea, and vomiting. Chills, sweating, fever, aching muscles and joints, and weight loss may also occur. With viral gastroenteritis, the temperature is usually no higher than 38 °C; fatigue and headache are possible. With bacterial infections, there may be blood in the stool and severe abdominal pain.

• nausea and vomiting
• diarrhea
• abdominal pain and cramps
• fever, headache, and muscle pain
• signs of dehydration: dry mouth, dark concentrated urine

How stomach flu spreads

Norovirus spreads through feces and is highly contagious: through close contact with a sick person, through surfaces and objects and then touching the mouth, through food prepared by an infected person, and through contaminated water. Gastroenteritis in general is transmitted through food and water, through dishes and utensils, and from person to person through close contact. Alcohol-based gels do not kill norovirus — hands should be washed with soap.

How stomach flu differs from true influenza

Viral gastroenteritis is not related to the influenza virus. It affects the stomach and intestines, and the leading symptoms are vomiting and diarrhea. The pathogens are norovirus, rotavirus, and other enteric viruses.

Possible complications and when to see a doctor

The main complication is dehydration; young children, older adults, and people with weakened immunity are especially vulnerable. In most people, the illness resolves within a few days without specific treatment. The doctor assesses signs of dehydration — dry mouth, infrequent urination, dizziness, absence of tears; if necessary, a stool test is ordered to identify the pathogen.

On its own, it is not a reason to call an ambulance; 103/112 — if an adult has vomiting with blood or vomit resembling coffee grounds, green vomiting, neck stiffness and pain when looking at bright light, sudden severe headache, sudden severe abdominal pain, blue or pale skin, labored breathing, or confusion.

This material is for reference: it explains what lies behind the name "stomach flu" but does not replace consultation with a doctor.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer