Acute gastritis is inflammation of the stomach and presents with nausea and vomiting. Enteritis is inflammation of the intestines and presents with diarrhoea. Gastroenteritis is inflammation all the way from the stomach to the intestines and presents with nausea, vomiting and diarrhoea.

The most common cause of gastroenteritis is viral. It is very easily spread and patients presenting with gastroenteritis often have an affected family member or contact.

It is essential to isolate the patient in a healthcare environment such as a hospital ward as they can easily spread it to other patients.

Most people recover well but beware that it can be potentially fatal especially in very young or old patients or those with other health conditions.


Viral Gastroenteritis

Viral gastroenteritis is the most common. Viral gastroenteritis is highly contagious.

  • Rotavirus
  • Norovirus
  • Adenovirus is a less common cause and presents with a more subacute diarrhoea


E. coli

Escherichia coli (E. coli) is a normal intestinal bacteria. Only certain strains cause gastroenteritis. It is spread through contact with infected faeces, unwashed salads or water.

E. coli 0157 produces the Shiga toxin. This causes abdominal cramps, bloody diarrhoea and vomiting. The Shiga toxin destroys blood cells and leads to haemolytic uraemic syndrome (HUS).

The use of antibiotics increases the risk of haemolytic uraemic syndrome therefore antibiotics should be avoided if E. coli gastroenteritis is considered.


Campylobacter Jejuni

Campylobacter is a common cause of travellers diarrhoea. It is the most common bacterial cause of gastroenteritis worldwide. Campylobacter means “curved bacteria”. It is a gram negative bacteria that is curved or spiral shaped. It is spread by:

  • Raw or improperly cooked poultry
  • Untreated water
  • Unpasteurised milk


Incubation is usually 2-5 days. Symptoms resolve after 3-6 days. Symptoms are:

  • Abdominal cramps
  • Diarrhoea often with blood
  • Vomiting
  • Fever


Antibiotics can be considered after isolating the organism where patients have severe symptoms or other risk factors such as HIV or heart failure. Popular antibiotic choices are azithromycin or ciprofloxacin.



Shigella is spread by faeces contaminating drinking water, swimming pools and food. The incubation period is 1-2 days and symptoms usually resolve within 1 week without treatment. It causes bloody diarrhoea, abdominal cramps and fever. Shigella can produce the Shiga toxin and cause haemolytic uraemic syndrome. Treatment of severe cases is with azithromycin or ciprofloxacin.



Salmonella is spread by eating raw eggs or poultry and food contaminated with infected faeces of small animals. Incubation is 12 hours to 3 days and symptoms usually resolve within 1 week. Symptoms are watery diarrhoea that can be associated with mucus or blood, abdominal pain and vomiting. Antibiotics are only necessary in severe cases and guided by stool culture and sensitivities.


Bacillus Cereus

Bacillus cereus is a gram positive rod that is spread through inadequately cooked food. It grows well on food not immediately refrigerated after cooking. The typical food is fried rice left out at room temperature.

Whilst growing on the food it produces a toxin called cereulide that causes abdominal cramping and vomiting within 5 hours of ingestion. When it arrives in the intestines it produces different toxins that cause a watery diarrhoea. This occurs more than 8 hours after ingestion. All of the symptoms usually resolves within 24 hours.

Therefore the typical course is vomiting within 5 hours, then diarrhoea after 8 hours, then resolution within 24 hours.

TOM TIP: The typical exam patient develops symptoms soon after eating leftover fried rice that has been left at room temperature. It has a short incubation period after eating the rice and they then recover within 24 hours. Examiners like this question because the course of bacillus cereus is easy to distinguish from the other causes of gastroenteritis.

Side Note: The other place you may come across bacillus cereus is in intravenous drug users (IVDU) that develop infective endocarditis. Staphylococcus is the most common cause of IE in IVDUs but Bacillus cereus is one to keep in mind.


Yersinia Enterocolitica

Yersinia is a gram-negative bacillus. Pigs are key carriers of Yersinia and eating raw or undercooked pork can cause infection. It is also spread through contamination with the urine or faeces of other mammal such as rat and rabbits.

Yersinia most frequently affects children causing watery or bloody diarrhoea, abdominal pain, fever and lymphadenopathy. Incubation is 4-7 days and the illness can last longer than other causes of enteritis with symptoms lasting 3 weeks or more. Older children or adults can present with right-sided abdominal pain due to mesenteric lymphadenitis (inflammation in the intestinal lymph nodes) and fever which can give the impression of appendicitis.

Antibiotics are only necessary in severe cases and guided by stool culture and sensitivities.


Staphylococcus Aureus Toxin 

Staphylococcus aureus can produce enterotoxins when growing in food such as eggs, dairy and meat. When eaten these toxins cause small intestine inflammation. This causes symptoms of diarrhoea, perfuse vomiting, abdominal cramps and fever. These symptoms start within hours of ingestion and settle within 12-24 hours. It is not actually the bacteria causing the enteritis but the staphylococcus enterotoxin.



Giardia lamblia is a type of microscopic parasite. It lives in the small intestines of mammals. These mammals may be pets, farmyard animals or humans. It releases cysts in the stools of infected mammals. These cysts then contaminate food or water and are eaten to infect a new host. This is called faecal-oral transmission.

Infection may not cause any symptoms or it may cause chronic diarrhoea. Diagnosis is made by stool microscopy. Treatment is with metronidazole.


Principles of Gastroenteritis Management

Good hygiene helps prevent gastroenteritis. When patients develop symptoms they should immediately be isolated to prevent spread. Barrier nursing and rigorous infection control is important for inpatients to prevent spread to other patients.

A sample of the faeces can be tested with microscopy, culture and sensitivities to establish the causative organism and antibiotic sensitivities.

Assess patients for dehydration. Attempt a fluid challenge and if they are able to tolerate oral fluid and are adequately hydrated consider outpatient management. If not vomiting and tolerated then rehydration solutions (e.g. dioralyte) can be used. If dehydrated then intravenous fluids can be used to rehydrate them and prevent dehydration until oral intake is adequate again.

Slowly introduce a light diet in small quantities once oral intake is tolerated again. Advise them to stay off work or school for 48 hours after symptoms have completely resolved.

Antidiarrhoeal medication such as loperamide and antiemetic medication such as metoclopramide are generally not recommended but may be useful for mild to moderate symptoms. Antidiarrhoeals should be avoided in e. coli 0157 and shigella infections and where there is bloody diarrhoea or high fever.

Antibiotics should only be given in patients that are at risk of complications and once the causative organism is confirmed.


Post-Gastroenteritis Complications

There are possible post-gastroenteritis complications:

  • Lactose intolerance
  • Irritable bowel syndrome
  • Reactive arthritis
  • Guillain–Barré syndrome


Last updated March 2019