Gastroenteritis is usually caused by a viral or bacterial infection, and less often by a parasitic infection. The most common causes of viral gastroenteritis are norovirus and rotavirus. Campylobacter, Escherichia coli (E. coli), and Salmonella are the most common causes of bacterial gastroenteritis. Parasitic gastroenteritis is usually caused by Giardia.
Viral gastroenteritis is the most frequent cause of gastroenteritis outbreaks, which occur when groups of people are affected at the same time and place. Norovirus outbreaks can affect both children and adults, while rotavirus mainly affects infants and children.
Campylobacter is the most commonly reported cause of foodborne illness in New Zealand, often found on raw chicken or raw red meat, and in unpasteurised milk. It has a 24-48 hour incubation time and symptoms can last for 5 to 8 days on average.
The most common cause of ‘food poisoning’ is preformed toxins that will cause vomiting within 6-8 hours of eating food with the toxin present. As most infections have an incubation time of more than 24 hours, a person cannot pick up an ‘infection’ from eating suspicious food. It is more likely there was a toxin in the food.
The people most at risk of gastroenteritis are:
- Infants and young children, who have an immature immune system
- The elderly, who have less efficient immune systems, and especially those living in nursing homes
- Children in day care, school children, and students living in dormitories
- Anyone with a weakened immune system, such as people with HIV/AIDS or receiving chemotherapy
Signs and symptoms
The main symptom of gastroenteritis is diarrhoea, which is when your bowel movements (faeces or stools) become watery and you need to go to the toilet frequently and urgently. Although diarrhoea is the primary symptom of gastroenteritis, there are many other symptoms and signs.
Additional symptoms and signs of gastroenteritis may include:
- Nausea and vomiting
- Abdominal pain and cramping
- Mild fever and chills
- Loss of appetite
- Headache and muscle aches
- Tiredness and general body weakness
- Incontinence (loss of control over bowel motions)
- Poor feeding in infants.
Depending on the cause, symptoms may appear within one to three days after infection and can range from mild to severe. Symptoms usually last a few days, but occasionally may persist for up to ten days.
You should contact your doctor if your symptoms don’t improve after a few days and/or increase in severity, your symptoms go away but come back, your stools become bloody or pussy, you have constant abdominal pain, you have been vomiting for more than two days, or if you develop dehydration. Dehydration can arise from the excessive loss of fluid from the body, which can occur quickly with gastroenteritis.
The signs and symptoms of dehydration include:
- Extreme thirst
- Not having urinated in the past eight hours or passing only a small volume of urine
- Urine that is dark in colour and smelly
- Dry lips and mouth, and a lack of tears
- Cold hands and feet
- Sunken cheeks or eyes
- Dizziness, lethargy, floppiness
- In infants, dry nappies (for longer than 4-6 hours) and/or a sunken fontanelle (the soft spot on the top of a baby’s head)
- Skin that ‘tents up’ when pinched.
Signs of dehydration in anyone, especially infants and children, the elderly, and people with weakened immune systems, are reasons to contact a doctor immediately.
Gastroenteritis is usually diagnosed by the symptoms that it produces, primarily diarrhoea. However, if the symptoms are severe or persistent, your doctor may take a stool (faeces) sample to identify the cause of the gastroenteritis.
Stool samples may be taken during outbreaks of gastroenteritis, such as those occurring on cruise ships and in hospitals and nursing homes, to identify the virus or bacteria that has caused the outbreak. Also, identifying patients with similar histories of food or drink they have recently consumed often helps to determine the source of the outbreak.
Most people with gastroenteritis recover within a few days without the need for medical treatment, as long as they stay properly hydrated.
To help keep yourself comfortable and prevent dehydration while you recover, try the following:
- Avoid dairy products, caffeine, alcohol, and nicotine
- Avoid sugary, fatty, or highly seasoned (spicy) foods
- Drink plenty of liquid every day, taking small, frequent sips, including clear thin broths or soups, diluted non-caffeinated sports drinks (e.g., Powerade or Gatorade), and rehydration formulas (e.g., Gastrolyte) that are available without prescription from a pharmacy
- Make sure that you get plenty of rest
- Avoid taking non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin, ibuprofen, and diclofenac, for pain relief as they can make your stomach more upset
- Paracetamol (e.g., Panadol) can be taken for fever and pain, but it should be used cautiously.
For infants with gastroenteritis, let the baby's stomach rest for 15 to 20 minutes after vomiting or a bout of diarrhoea, then offer small amounts of liquid. Let the baby nurse if being breast-fed. If you are bottle-feeding, offer a small amount of an oral rehydration solution or regular formula.
Anti-diarrhoeal medications, such as Imodium, can be taken to slow the diarrhoea. In most cases, however, it is better for the body to clear itself of the virus or bacteria causing the gastroenteritis.
Use of antibiotics is usually avoided because they are not effective against viruses, and their overuse contributes to the development of antibiotic-resistant strains of bacteria.
The following actions can be taken to avoid getting and spreading gastroenteritis:
- Frequent and thorough hand washing, especially before eating or preparing food, and after going to the toilet or contact with an infected person
- Ensure that children wash their hands frequently and thoroughly
- Avoid direct contact with infected individuals, if possible
- Stay home from work and keep children away from day care or school until symptoms have gone
- Washing the clothing, bedding, and toys of an infected person
- Cleaning and disinfecting kitchen surfaces, especially after working with raw meat or chicken, or eggs
- Avoid eating undercooked foods, especially meat, chicken, and fish
- Avoid drinking untreated water
- Avoid eating raw meats, fish, and shellfish unless you are sure that they have been freshly prepared and are from a reliable source
- Thoroughly wash any fresh produce, such as fruits and vegetables
- Have your infant or child vaccinated with a rotavirus vaccine, which can prevent gastroenteritis caused by rotavirus
- When travelling, drink only bottled or boiled water and avoid ice cubes, especially in developing countries.
A vaccine for rotavirus is available free for New Zealand babies to have before 15 weeks of age. The oral vaccine is given in two doses (at the 6-week and 3-month immunisation visits) to reduce the incidence or severity of rotavirus infection, which is a very common cause of gastroenteritis in infants and young children.
Further information and support
Free phone: 0800 611 116
Free phone: 0800 933 922
Mayo Clinic (2018). Viral gastroenteritis (stomach flu) (Web Page). Rochester, MN: Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/viral-gastroenteritis/symptoms-causes/syc-20378847 [Accessed: 07/04/21]
Ministry of Health (2017). Guidelines for the management of norovirus outbreaks in hospitals and elderly care institutions (Web Page). Wellington: New Zealand Government Ministry of Health. https://www.health.govt.nz/publication/guidelines-management-norovirus-outbreaks-hospitals-and-elderly-care-institutions [Accessed: 07/04/21]
Ministry of Health (2018). Rotavirus (Web Page). Wellington: New Zealand Government Ministry of Health. https://www.health.govt.nz/your-health/conditions-and-treatments/diseases-and-illnesses/rotavirus [Accessed: 07/04/21]
NHS inform (2020). Gastroenteritis (Web Page). Glasgow: National Health Service (NHS) Scotland. https://www.nhsinform.scot/illnesses-and-conditions/stomach-liver-and-gastrointestinal-tract/gastroenteritis [Accessed: 07/04/21]
O’Toole, M.T. (Ed.) (2017). Gastroenteritis. Mosby’s Dictionary of Medicine, Nursing & Health Professions (10th ed.). St Louis, MI: Elsevier.
Reviewed: April 2021