Stomach flu, or acute gastroenteritis, usually strikes fast: vomiting, diarrhoea, stomach pain and sometimes fever. The great majority of cases are caused by viruses such as norovirus or rotavirus and clear up on their own within a few days. The heart of the treatment is not a medicine but fluids. The doctor's job is to recognise dehydration and the few situations where something else is behind the pain or the diarrhoea.
How stomach flu runs its course
Symptoms typically begin 1–2 days after infection. Vomiting usually lasts less than a day, diarrhoea a few days. Fever is generally mild. You may feel weak for a couple of days after the symptoms stop, and the gut can react to food for a week or so.
Stomach flu spreads easily. Wash your hands with soap, especially after using the toilet and before preparing food, use your own towel and stay home for a couple more days after the symptoms end, particularly if you work with food, children or people who are ill.
Fluids are the main treatment
Vomiting and diarrhoea lose water and salts. The aim is to replace them as fast as they are lost.
- Drink small amounts often. A large gulp easily comes straight back up; a spoonful or a small sip every few minutes stays down better.
- Oral rehydration powder from the pharmacy is the best drink, because it has the right balance of salts and sugar. For adults, diluted juice or water with a salty biscuit also works.
- Avoid sweet fizzy drinks, energy drinks and concentrated juice, which can make diarrhoea worse.
- Eat when you feel like it. No special diet is needed; start with light food such as porridge, soup or toast.
- Anti-diarrhoeal medicine (loperamide) can give an adult short-term relief when used as the package leaflet directs, but it is not used when there is fever or blood in the stool, and not in children. If the diarrhoea has not improved within 48 hours, stop the medicine and seek a doctor's assessment.
- Antibiotics are usually not needed, because the cause is most often a virus.
Children and older people dehydrate easily
A small child loses proportionally far more fluid than an adult. Under Finnish Current Care guidelines, stomach flu in a child is treated with oral rehydration solution in small, frequent doses; breastfeeding continues, and normal food is resumed as soon as the child can manage it. A vomiting child usually drinks best from a spoon or a syringe every few minutes.
In older people the sense of thirst is weaker, and many medicines, such as diuretics and blood pressure tablets, raise the risk of dehydration. Stomach flu in an older person deserves more caution than in a young adult.
Signs of dehydration are a dry mouth and tongue, little or darker urine, dry nappies and crying without tears in a child, tiredness and floppiness, sunken eyes and dizziness on standing up.
A doctor's assessment is worthwhile if
- vomiting continues for more than a day or you cannot drink
- diarrhoea lasts more than a week
- the fever is high or continues for several days
- you have returned from abroad and the diarrhoea is dragging on
- the person who is ill is under six months old, elderly or has several illnesses
- you have inflammatory bowel disease, diabetes or medication that weakens your immune system
- you are pregnant and the symptoms are severe
Go to the emergency department or call 112 immediately if
- there is blood in the stool or the stool is black
- the stomach pain is severe, constant or focused in one spot, especially the lower right abdomen
- there are clear signs of dehydration: no urine for many hours, a child who is floppy or hard to wake, an older person who is confused
- the vomit contains blood or looks like coffee grounds
- breathing is rapid or the pulse is very fast at rest
- the abdomen is rigid and tender to touch
- the person who is ill is a baby who is not drinking at all
Severe dehydration is treated with intravenous fluids and cannot be managed at home or remotely.
How Treat can help
If you are unsure whether self-care is enough, you can describe your symptoms in Treat in your own words. A licensed doctor usually assesses the situation within minutes during service hours, gives rehydration advice, writes a sick leave certificate if needed and tells you whether the situation calls for tests or a visit. Treat is not an emergency service: with signs of dehydration or severe stomach pain, go to the emergency department or call 112.
This article is general health information and does not replace an individual assessment by a doctor.