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Gastroenteritis (colloquially known by many names, including gastric flu, “gastro”, vomiting and diarrhoea, “food poisoning”, “the squits”is a very common presentation to general practice and emergency departments, in people of all ages, but especially in children, or families with young children.

Gastroenteritis is a broad term, but usually used to refer to an infective illness which causes diarrhoea, vomiting and often abdominal pain. The majority of cases are viral, and a smaller percentage are true “food poisoning” (usually bacterial, occasionally parasitic) related to improper preparation or storage of food.

It typically occurs in outbreaks in winter (often rotavirus or norovirus – “winter vomiting virus”), and may cause hospital wards to be shut down during an outbreak.

In most patients with vomiting and diarrhoea together, gastroenteritis should be considered as the most likely diagnosis. In patients with vomiting only, or diarrhoea only, particularly in the presence of fever or abdominal pain, caution should be applied and a careful history and examination undertaken to look for other – often more serious – causes. In children in particular, vomiting alone can be a sign of a more serious underlying illness.

The cause is not usually identified – and most cases are self limiting and resolve in a few days. The treatment does not usually depend on the cause, and typically consists of managing nausea and vomiting and encouraging oral fluid intake. Severe cases of dehydration may require hospital admission for IV fluid administration.

In developing countries, gastroenteritis is a leading cause of death.

Epidemiology & Aetiology

  • Affects about 20% of the population each year
  • Viral infections cause 30-40% of cases in developed countries
    • In children, the proportion caused by viruses is much greater
  • Risk factors
    • Poor sanitation / poor personal hygiene
    • Immunocompromised patients
    • Poor food preparation
      • Undercooked
      • Reheated – reheating food correctly will kill bacteria, but will not destroy any toxins they left behind
      • Left at room temperature for too long
      • Particularly at risk foods include seafood


Viral causes are by far the most common. In the UK, norovirus – the “winter vomiting virus” is renowned for causing outbreaks on hospital wards

Common organisms include:

  • Viral causes
    • Norovirus
    • Rotavirus – very common in young children
    • Adenovirus – very common in young children
    • Enterovirus
    • Ebola – recent deadly outbreaks in Africa
    • Viral causes are usually person-to-person direct transmission, although infected food handlers may also cause outbreaks via food without direct contact.
  • Bacterial Causes
    • Campylobacter ( most commonly from raw / undercooked chicken)
    • Escherichia Coli (undercooked mince or meat, raw milk, contaminated vegetables)
    • Salmonella (most commonly from raw eggs)
    • Shigella
    • Staphylococcus – usually the toxins from the bug rather than the bug itself
    • Bacterial causes are more likely to cause blood in the diarrhoea than viral causes. Bacterial causes are also usually commonly clustered around food outbreaks. 
  • Parasites
    • Giardia
    • Entamoeba (amoebiasis)
    • Cryptosporidium (from contaminated water)
    • Parasitic causes may also cause bloody diarrhoea but tend to have longer incubation periods than bacterial infections


Vomiting poop emoji

  • Diarrhoea – often watery – multiple episodes – up to 10x per day is not unusual
  • Vomiting – again can be frequent – up to 10x daily
  • Typical incubation periods:
    • Virus – 1 day
    • Bacterial – hours to days (up to 4 days)
    • Parasite – 7-10 days
  • Bloody diarrhoea makes a bacterial presentation more likely – e.g. E. Coli O157 or salmonella or E. histolyica (not commonly seen in UK)
  • Children are more likely to be febrile with an infective gastroenteritis
  • In adults, fever may be indicative of a more serious cause


  • Heart rate
  • Blood pressure
  • Temperature
  • Abdominal examination – often non-specific tenderness
  • Degree of dehydration
    • Less than 5% – MILD
    • 5-10% – MODERATE
      • Any of the above, PLUS
      • Dizziness
      • Tiredness
      • Muscle cramps
      • Dry tongue . mucus membranes
      • Sunken eyes (+/- sunken fontanelle in young children)
      • Reduced skin turgor
      • Postural hypotension with systolic BP dropping to <90
      • Tachycardia
    • 10% or more – SEVERE
      • Any of the above, PLUS
      • Oligouria
      • Confusion
      • Weakness
      • In children – floppy / unresponsive
      • Tachycardia
      • Reduced capillary refill time
      • Systolic BP <90

Differential diagnoses

Almost anything that causes diarrhoea or vomiting can be considered as a differential diagnosis, and hence the potential list is extremely long. Below are some common examples


Stool MC+S is not routinely performed, but should be considered if:

  • Blood or mucus in the stool
  • Patient known to be immunocompromised
  • Symptoms not resolving after 7 days
  • Recent overseas travel
  • Any uncertainty about diagnosis

In patients who are severely unwell – e.g. severe dehydration, consider:

  • FBC
  • Urea + electrolytes
  • Specific investigations to rule out other causes – e.g USS or CT abdomen


Indications for hospital admission

  • Signs of severe dehydration
  • Consider if not yet severely dehydration, but unable to retain fluids orally
  • Consider if social circumstances may not be amenable to safe care at home – e.g. elderly or isolated, underlying medical conditions

Outpatient Management

  • Oral rehydration is the mainstay of treatment
    • In adults, there is no evidence that oral rehydration solutions (e.g. dioralyte, hydralyte) are any more effective than water, although they are frequently recommended
    • Titrate to urine output
    • In children, oral rehydration solutions should be used, or watered-down apple juice (5 parts water, one part apple juice) is an alternative. Children can be reluctant to drink solutions. If parents are struggling, use a syringe, with small amounts regularly – e.g. 1ml/Kg every 5 minutes). Continue to offer breast milk if the child is usually feeding via this method
    • Aim for 50ml/Kg every 4 hours
    • Aim to record the fluid intake on a fluid chart
    • Vomiting is NOT a contraindication to oral rehydration – contrary to popular belief, it doesn’t “all come back up again” and significant amounts are often still absorbed
    • Consider IV fluids if not responding to oral intake
    • NG tube is an alternative to IV fluid in children
  • Food intake:
    • Guided by appetite
    • Small frequent meals
    • Avoid fatty and spicy foods
    • Plain starchy foods considered best
    • NO evidence for fasting or avoidance of solid food intake
    • In children – feed as directed by the child
  • Reducing the spread of infection
    • Frequent hadn’t washing is effective at reducing the spread of infection
    • Do not share towels
    • Wash any soiled bed sheets, separately from other clothes and at the highest temperature recommended on washing label
    • Recommend cleaning bathroom surfaces – e.g. taps, door hands, toilet flush and toilet seat at least daily
    • Norovirus is partially resistant to alcohol hand gel, and C. difficile spores are not killed by alcohol. As such, hand washing with soap and water is recommended
  • School / work exclusion
    • Exclude for 48 hours from the last episode of diarrhoea or vomiting
    • Some guidelines recommend 24 hours instead of 48 hours
  • Anti-emetics
    • states “not usually necessary in primary care” – my personal experience in primary care and as an Emergency Department Registrar in Australia is that they are VERY frequently prescribed – especially in children – in primary care and emergency departments.
    • Often ondansetron (private prescription only for this indication in both UK and Australia, and previously prohibitively expensive but now retails for <£5GBP or <$20AUD for 4 tablets of 4mg) is the most effective – 4mg single dose (or 2mg TDS in children between 8-16kgs, not recommended in children <8kgs, but in emergency departments sometimes given as 0.15mg/Kg doses). Particularly useful as it comes in an orally dispersible “wafer” which dissolves on or underneath the tongue and thus doesn’t require the patient to swallow a tablet with water in severe cases of vomiting. Often a single dose only is required – symptoms are usually much improved by 8 hours when a second dose can be given if required.
    • Metoclopromide – 10mg TDS in adults is another option
    • Cyclizine – 50mg TDS – an antihistamine – frequently used for nausea and vomiting on the NHS – because it is cheap!
  • Anti-diarrhoea drugs – e.g. loperamide (“Immodium” or “gastro-stop”)
    • Not usually recommended
    • Are available over the counter and often patients have tried these before presentation
    • Carry a rare risk of bowel obstruction
    • Anecdotally in my practice seem to be associated with a longer duration of abdominal pain and bloating
    • Should NEVER be used if fevers or blood or mucus in stool
    • I rarely prescribe them if someone has an event they really can’t miss (e.g. wedding, funeral, job interview – although generally they should be isolating themselves anyway), with full disclosure of the above risks
  • Antibiotics are almost never indicated
    • Most cases are viral
    • Even in a bacterial cause, most cases will resolve in a few days without the use of antibiotics. In common bacterial causes – such as E Coli or shigella, antibiotics can react with toxins and cause haemolytic uraemia syndrome and thus should still be avoided
  • Notifiable diseases
    • Be aware of the results of any stool MC+S samples – as many identifiable causes are notifiable diseases


  • Dehydration and electrolyte disturbance are the main complications
  • Haemolytic uraemia syndrome – rare. Features include acute kidney injury, haemolytic anaemia and thrombocytopenia. Usually occurs in very young children or frail elderly adults
  • Bacterial causes may cause reactive symptoms which are sometimes delayed in presentation by several weeks. These can include:
  • Salmonella is associated with a risk of systemic and secondary organ infection
  • Toxic megacolon – rare
  • Guillian-Barre Syndrome associated with viral infection
  • Lactose intolerance – often transient
  • Be aware of reduced medication absorption – particularly important examples include oral contraceptives and anti-convulsants


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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

This Post Has One Comment

  1. Milan Roemer

    Really good web site. Helps me much starting as doc in Scotland, even with nearly 15 years as medicine man on the back. Good structure and well chosen topics. Sometimes links are some difficult, but guess thats normal.
    Like it.

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