Onset of stomach flu: what to know

Stomach flu is a common name for gastroenteritis, inflammation of the stomach and intestines. It is not the same illness as influenza. Vomiting, loose stools, nausea, abdominal pain, reduced appetite, and fever may appear in different combinations. Viral infections, including rotavirus infection, are one possible cause; contaminated food, water, or close contact can also spread infection.

The main concern is dehydration. Dry mouth, dizziness, unusual tiredness, very dark urine, or passing urine less often can signal that the body is losing more fluid than it replaces.

Take frequent small sips of water or an oral rehydration drink. If vomiting makes drinking difficult, pause briefly and try smaller amounts more often. When appetite returns, choose simple foods that you tolerate and continue fluids. Rest, wash hands carefully with soap and water, and avoid preparing food for others while you are unwell. Do not take antibiotics unless a clinician prescribes them, because many cases are not bacterial.

Seek urgent care for severe or worsening abdominal pain, blood in vomit or stool, confusion, fainting, inability to keep fluids down, or signs of significant dehydration. Infants, older adults, pregnant people, and people with serious long-term conditions may need advice earlier. Contact a clinician if fever is concerning, symptoms are persistent, or you are unsure how to replace fluids safely.

Ask which rehydration drink is suitable, whether your medicines need adjustment during vomiting or diarrhoea, and which changes in urine, pain, or alertness should prompt urgent review.