An intestinal infection can cause diarrhoea, vomiting, nausea, fever and stomach cramps. Viruses are the most common cause, but bacteria and parasites can also be responsible. Most mild infections improve without specific treatment, although dehydration and certain warning signs require medical care.
Common causes
Infections spread when germs from faeces or vomit reach another person’s mouth. This can happen through contaminated food or water, unwashed hands, shared surfaces or close contact with someone who is ill.
- Viruses: norovirus and rotavirus are common causes of gastroenteritis.
- Bacteria: Campylobacter, Salmonella, Shigella and some types of E. coli may be linked to contaminated food, water or animals.
- Parasites: Giardia and other parasites may spread through contaminated water, food or close contact.
Symptoms alone cannot always identify the cause. A clinician may request a stool sample when illness is severe, persistent, linked to travel or part of a suspected outbreak.
Symptoms
Symptoms may begin within hours or several days after exposure and can include:
- watery diarrhoea
- nausea or vomiting
- cramping or abdominal pain
- fever, headache or aching muscles
- loss of appetite and tiredness
Blood or mucus in the stool, severe localised pain or a high fever can suggest a more serious illness and should not be ignored.
Preventing dehydration
Replacing lost fluid is the main treatment. Take frequent small sips if vomiting makes drinking difficult. An oral rehydration solution from a pharmacy can replace water, salts and sugar in the right proportions. Babies, older adults and people with chronic illness can become dehydrated more quickly.
Signs of dehydration include a dry mouth, intense thirst, dark urine, passing less urine, dizziness and unusual tiredness. In babies, look for fewer wet nappies, no tears when crying, a sunken soft spot or unusual drowsiness.
Eat when you feel able. Most people can gradually return to their normal diet. Antibiotics do not treat viral infections and are only useful for selected bacterial infections after clinical assessment.
How to avoid spreading the infection
- Wash hands thoroughly with soap and water after using the toilet, changing nappies and before preparing food.
- Do not prepare food for other people while you are ill.
- Clean toilets, taps and frequently touched surfaces regularly.
- Wash soiled clothes and bedding separately at the hottest suitable temperature.
- Do not share towels, cutlery or utensils.
- Stay away from work, school or nursery until at least 48 hours after vomiting and diarrhoea have stopped, unless local public health advice says otherwise.
Alcohol hand gel does not reliably kill every germ that causes gastroenteritis, so soap and water are particularly important.
When to seek medical advice
Contact a healthcare professional promptly if:
- you cannot keep fluids down
- there are signs of dehydration
- diarrhoea contains blood or is black
- you have a high fever, severe or worsening pain, or a swollen abdomen
- symptoms began after recent foreign travel, antibiotics or a hospital stay
- diarrhoea lasts more than seven days or vomiting lasts more than two days
- the person affected is a baby, frail older adult, pregnant, immunocompromised or has a serious long term condition
Call your local emergency number for confusion, collapse, severe breathing difficulty, very severe abdominal pain or signs of shock.
After the infection
The bowel can remain sensitive for a short time after the infection has cleared. If diarrhoea, bloating or pain continues or keeps returning, arrange a medical assessment rather than assuming it is still an infection. Persistent symptoms can have other causes, including irritable bowel syndrome, but a diagnosis should be made by a qualified professional.
Sources
Reviewed: 28 August 2026
Medical disclaimer: This information is general and does not replace an individual medical assessment. Seek urgent help for severe or rapidly worsening symptoms.