Acute gastritis is stomach inflammation and presents with epigastric discomfort, nausea and vomiting. Enteritis is inflammation of the intestines, and presents with abdominal pain and diarrhoea. Gastroenteritis is inflammation of the stomach and intestines and presents with pain, nausea, vomiting and diarrhoea.
The most common causes of gastroenteritis are viruses. Viral gastroenteritis spreads easily, and patients often have an affected household member or contact. It is essential to isolate the patient in a healthcare environment, such as a hospital ward or assessment unit, to prevent spread to other patients.
Most people recover well. However, gastroenteritis can rarely be fatal, especially in very young or frail elderly patients.
Viral Gastroenteritis
Viral gastroenteritis is common. It is highly contagious. Specific viruses include:
- Rotavirus (typically causes watery diarrhoea lasting 5-7 days)
- Norovirus (typically causes rapid-onset severe vomiting lasting 12-48 hours)
- Adenovirus (typically causes respiratory symptoms, but can cause diarrhoea, especially in young children)
Escherichia Coli
Escherichia coli (E. coli) is a normal intestinal bacterium. Only certain strains cause gastroenteritis. It is spread through contact with infected faeces, unwashed salads and contaminated water.
E. coli O157 produces the Shiga toxin. The Shiga toxin causes abdominal cramps, bloody diarrhoea and vomiting. It also destroys red blood cells, leading 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 a possibility.
Campylobacter Jejuni
Campylobacter is a common cause of travellers’ diarrhoea. It is the most common bacterial cause of gastroenteritis worldwide. It is a gram-negative, curved or spiral-shaped bacterium. It is spread by:
- Raw or improperly cooked poultry
- Untreated water
- Unpasteurised milk
Incubation is usually 2 to 5 days. Symptoms resolve after 3 to 6 days. Symptoms are:
- Abdominal cramps
- Diarrhoea, often with blood
- Vomiting
- Fever
Antibiotics can be considered after isolating the organism in patients who have severe symptoms or other risk factors, such as HIV or heart failure. Clarithromycin is often first-line. Azithromycin and ciprofloxacin are alternative options.
Shigella
Shigella is spread via faeces, either person-to-person or through contaminated drinking water or food. The incubation period is 1-2 days, and symptoms usually resolve within one week. It causes bloody diarrhoea, abdominal cramps and fever. Shigella can produce the Shiga toxin, which can cause haemolytic uraemic syndrome. Treatment of severe cases is with azithromycin or ciprofloxacin.
Salmonella
Salmonella is spread by eating raw eggs or poultry or food contaminated with the infected faeces of small animals. The incubation period is 12 hours to 3 days, and symptoms usually resolve within one week. Symptoms are watery diarrhoea, which may be associated with mucus or blood, abdominal pain and vomiting. Antibiotics are only necessary in severe cases and are guided by stool culture and sensitivities (e.g., ciprofloxacin).
Bacillus Cereus
Bacillus cereus is a gram-positive rod spread through contaminated cooked food. It grows on food not immediately refrigerated after cooking (e.g., fried rice or cooked pasta left 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. Reheating the food can kill the bacteria, but does not destroy the cereulide toxin. When Bacillus cereus reaches the intestines, it produces toxins that cause watery diarrhoea. Diarrhoea occurs more than 8 hours after ingestion. All of the symptoms usually resolve within 24 hours.
The typical course is vomiting within 5 hours, diarrhoea after 8 hours and resolution within 24 hours.
TOM TIP: The typical Bacillus cereus exam patient develops symptoms soon after eating fried rice left at room temperature, then recovers within 24 hours. Examiners like Bacillus cereus because it is easily distinguished from other causes of gastroenteritis.
TOM TIP: You may also come across Bacillus cereus with infective endocarditis in intravenous drug users (IVDU), where heroin is contaminated. However, Staph aureus is the most common cause of infective endocarditis in IVDU.
Yersinia Enterocolitica
Yersinia enterocolitica is a gram-negative bacillus. Pigs are key carriers, and eating raw or undercooked pork can cause infection. It is also spread through contact with infected humans, animals or faeces.
Yersinia typically affects children, causing watery or bloody diarrhoea, abdominal pain and fever. Incubation is 4-7 days. It can last longer than other causes of enteritis, with symptoms lasting 3 weeks or more. Older children and 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 are guided by stool culture and sensitivities.
Yersinia pestis (a different species of Yersinia) is spread through rat flea bites and causes plague.
Staphylococcal Enterotoxins
Staphylococcus aureus can produce enterotoxins when growing on foods such as eggs, dairy and meat. When eaten, these toxins cause rapid-onset vomiting and diarrhoea. These symptoms start within hours of ingestion and settle within 12 to 24 hours. It is the enterotoxin, not the bacteria, that causes the symptoms.
Giardiasis
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 faeces. The cysts may contaminate food or water. When eaten, they infect a new host. This is called faecal-oral transmission.
Infection may not cause any symptoms, or it may cause chronic diarrhoea. Typical symptoms include foul-smelling, greasy stools, bloating and flatulence. Diagnosis is made by stool testing (NAAT or EIA testing). Treatment is with tinidazole or metronidazole.
General Principles of Management
Food poisoning is a notifiable disease. The UK Health Security Agency (UKHSA) should be notified of suspected cases. When notifiable organisms (e.g., Campylobacter or Salmonella) are identified on testing, the lab must notify UKHSA.
Good hygiene helps prevent gastroenteritis. When patients develop symptoms, they should be immediately isolated to prevent spread. Barrier nursing and rigorous infection control are important for inpatients. Hand washing with soap and water is essential, as alcohol gel is insufficient for certain organisms (e.g., norovirus).
A faecal sample can be tested by PCR or culture to identify the causative organism and determine antibiotic sensitivities. This is not always required, as most cases are self-limiting. A stool culture is arranged when symptoms last for 7 days or more, or when there are more severe features (e.g., blood, systemic illness, foreign travel, suspected food poisoning, or the patient is immunocompromised).
Dehydration is the primary concern. The key to management is determining whether the patient can maintain hydration or requires admission for IV fluids. Antibiotics are generally not recommended or required. Most patients make a full recovery with simple, supportive management.
Oral rehydration salt solution (e.g., Dioralyte sachets mixed with water) can help replace losses in patients at increased risk of dehydration (e.g., frail patients). They contain glucose, potassium and sodium.
Antidiarrhoeal drugs (e.g., loperamide) and antiemetics (e.g., metoclopramide) are mostly avoided, as they can worsen the condition. Antidiarrhoeal drugs may be helpful for mild-to-moderate diarrhoea, but should not be used in E. coli O157, Shigella, or bloody diarrhoea.
Antibiotics are usually not recommended or required. Use depends on severity, risk factors, suspected organism, travel history and microbiology/local guidance. Where possible, stool testing should be performed before antibiotics are prescribed, but treatment may be started empirically in severe illness or high-risk patients.
Once the oral intake is better tolerated, a light diet with small quantities of bland foods can be introduced. Patients should stay off work or school until 48 hours after symptoms resolve entirely.
Post-Gastroenteritis Complications
After an episode of gastroenteritis, patients can develop:
- Lactose intolerance
- Irritable bowel syndrome
- Reactive arthritis
- Guillain–Barré syndrome
- Haemolytic uraemic syndrome
Last updated May 2026
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