Gastroenteritis | Pokenga whēkau

Gastroenteritis (adults)

Key points about gastroenteritis

  • Gastroenteritis (pokenga whēkau) is a gut infection that causes stomach cramps, vomiting and diarrhoea lasting from a few days up to a month.
  • The term gastroenteritis covers tummy bugs, food poisoning, traveller's diarrhoea, viral enteritis and intestinal flu.
  • It's often caused by drinking water or food that's been contaminated by bugs (viruses, bacteria or parasites).
  • It's important to stay hydrated by drinking plenty of fluid. This is especially important for older adults and children.
  • Wash your hands carefully to stop the spread.
Young man tramping holds stomach in pain
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Gastroenteritis is very common in New Zealand and is often caused by unclean food or water.

Your stomach upset may be due to:

  • a virus passed on by someone who may or may not have symptoms
  • bacteria from food that is not fresh or well cooked, or unclean water, hands, cooking or eating utensils
  • amoebas or parasites from food or water
  • toxins from bacteria or virus.

Common food that could be contaminated by bugs are meat, poultry, dairy products, eggs, shellfish and parboiled rice.

The infection irritates your stomach and gut, making the muscles tighten and causing vomiting or diarrhoea. You can get sick from an hour to 5 days after getting infected, depending on the type of bug.

Symptoms include:

  • diarrhoea (can be watery, bloody or mucous)
  • stomach cramps
  • feeling sick and weak
  • lethargy
  • loss of appetite
  • feeling shivery
  • headache
  • fever.

These symptoms usually only last a few days, but may last up to few months depending on the cause.

If your faeces (poo) contain blood or pus, contact your doctor. You should also see your doctor immediately if you:

  • become very weak
  • feel drowsy
  • have sunken eyes
  • go very pale
  • stop passing urine
  • get very dry skin or tongue.

You could be dehydrated and require rehydration immediately. Read more about dehydration.


Diagnosis is mostly based on your symptoms. If they are very bad or not settling, the doctor may send a stool (faeces/poo) sample to the laboratory to identify the type of bug that is causing your infection.


Most people usually recover without needing any medicine. The best thing to do when you have gastroenteritis is rest and drink small amount of fluids often to prevent dehydration. Older adults and children are most at risk of dehydration.

There are medicines to stop diarrhoea or vomiting. However, it is important to see your doctor before you use these medicines as this could prevent your body from getting rid of the bug.

See our topic on diarrhoea for self-help and treatment options for diarrhoea and/or vomiting (includes information on children and dehydration), and when to contact your doctor.

Gastroenteritis is not usually serious and most people recover without seeing a doctor. However, some people may need to see a doctor and get treated in a hospital if they get dehydrated, such as:

  • older adults
  • children less than 6 months old.

Read more about gastroenteritis in children and dehydration.

Here are some self-care measures that you can do when you have gastroenteritis:

  • get plenty of rest
  • drink small amount of fluids often
  • avoid tea, coffee, alcohol and dairy products
  • avoid fatty, oily or sugary food and drinks
  • take oral rehydration salts if needed (these are available at local pharmacies without prescription).

Careful handwashing is the most important way to prevent the spread of bugs causing gastroenteritis. Also, don’t go to school, day care or your workplace until you have had no symptoms for 48 hours.

Handling food

  • Wash your hands before eating or preparing food and after going to the toilet.
  • If you work with food commercially, use latex gloves and avoid touching food with your hands where possible.
  • Wash the tops of cans before opening.
  • Wash all utensils, boards and surfaces used for meat, poultry and seafood with hot, soapy water.
  • If it smells bad or looks off, throw the food out.


  • Buy fresh food only as you need it.
  • Get fresh food home from the supermarket and into the fridge quickly.
  • Check use-by dates and don’t eat food that has passed this date.
  • Don't leave poultry or meat in their store wrappers for more than 2 days. Rewrap it in wax paper or plastic wrap.
  • When freezing food, wrap it tightly, date it and use it within 6 months.


  • Never defrost frozen food on the bench. Thaw in the fridge, in warm water or in the microwave or cook it from frozen.
  • When thawing frozen meat in the fridge, put a plate underneath and place the meat on the bottom tray of the fridge to avoid contaminating other foods with meat drips.
  • Cook food thoroughly, particularly meat, chicken, eggs, milk products, fish and shellfish.
  • Cook chicken right through until the juices run clear. If you are using stuffing, pack it loosely.
  • Serve hot food hot (most bacteria are killed at 100°C) and cold food cold (bacteria stop growing at 0°C but can survive). Bacteria grow extremely well between 15°C and 51°C.
  • Cool leftovers quickly and place in the fridge. Reheat them until steaming hot and don’t reheat more than once.
  • Avoid raw fish, meats and shellfish unless you are sure they are well prepared and from a reliable place.

Travelling/eating out

  • Look at how clean the café or restaurant is.
  • Avoid food, even salad and cold cuts, that sits in a cabinet all day.
  • In developing countries, don't eat raw food, food from street stalls or peeled fruits; drink only bottled or boiled water or drinks; avoid ice and use water purification tablets.

The following links provide further information about gastroenteritis. Be aware that websites from other countries may have information that differs from New Zealand recommendations.

Gastroenteritis – causes, symptoms, treatment(external link) Southern Cross, NZ
Gastroenteritis(external link) KidsHealth, NZ, 2017
Gastroenteritis(external link) Bupa, UK
Gastroenteritis(external link) Better Health Channel, Australia


Gastroenteritis (tummy bug) [PDF, 233 KB] Hawkes Bay Public Health Unit, NZ, 2017
Viral gastroenteritis(external link) Regional Public Health, 2017


  1. Acute gastroenteritis (and toxin-related illnesses)(external link) Ministry of Health, NZ, 2018
  2. Gastroenteritis (tummy bug) information sheet [PDF, 233 KB] Hawkes Bay Public Health Unit, NZ
  3. Assessment and management of infectious gastroenteritis(external link) BPAC, NZ, 2009
  4. Top 5 food safety factors(external link) Ministry for Primary Industries, NZ, 2020


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Credits: Healthify editorial team. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Dr Derek JY Luo, MBChB (Otago) FRACP, Consultant Gastroenterologist

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