TL;DR: Acute diarrhoea is defined as three or more loose, watery stools a day. The most common causes are infections, side effects of medicines and digestive disorders. In mild cases, it can be treated at home by replenishing fluids, but a medical examination is necessary if there is blood in the stools, a high fever or if symptoms persist for more than 3–4 days.
Almost everyone experiences sudden diarrhoea at some point in their lives. It can start within a few hours and strikes even at the worst possible moments – and whilst it is usually harmless, it can sometimes be a sign of a serious illness. This article summarises what can cause sudden diarrhoea, when to see a doctor, and what you can do to relieve the symptoms at home. You’ll also learn about the most important warning signs, in which case you should not delay consulting a specialist.
What counts as sudden diarrhoea?
According to the medical definition, diarrhoea is defined as having mushy or watery stools (type 6 or 7 on the Bristol Stool Scale) at least three times a day, which differs from the individual’s usual bowel habits.
Acute diarrhoea lasts for up to 14 days. If symptoms persist for 14–30 days, this is referred to as persistent diarrhoea. Any diarrhoea lasting longer than 30 days is considered chronic diarrhoea, which is usually caused by a more serious underlying digestive disorder.
Sudden diarrhoea – particularly if it is bloody, accompanied by a high fever, or occurs in an elderly person or someone with a weakened immune system – requires immediate medical attention.
What can cause sudden diarrhoea?
Sudden diarrhoea can be caused by a number of different factors. Below, we look at the most common ones.
Infectious causes
The most common cause of sudden diarrhoea is infection. In the United States, an estimated 76 million cases of foodborne illness occur each year, resulting in 325,000 hospital admissions and 5,000 deaths – this clearly illustrates the seriousness of this public health problem.
The most common infectious agents:
- Bacteria: Salmonella, Campylobacter, Shigella, E. coli (various strains), Clostridium difficile, Vibrio cholerae
- Viruses: rotavirus, norovirus (Norwalk virus), adenovirus
- Parasites: Giardia lamblia, Entamoeba histolytica (amoeba), Cryptosporidium
- Food poisoning: Bacillus cereus (e.g. 1–6 hours after reheating rice), Clostridium perfringens (8–24 hours after eating beef or poultry), Staphylococcus aureus
Campylobacter, for example, is the most common cause of bacterial diarrhoea in the United States, causing approximately 2 million cases each year. Salmonella causes 1.5 million cases a year; symptoms typically appear within 48 hours of consuming contaminated eggs, poultry or dairy products.
Diarrhoea caused by the side effects of medicines
Diarrhoea is a well-known side effect of many medicines:
- Antibiotics (particularly broad-spectrum preparations – these can disrupt the balance of gut flora and may also contribute to Clostridium difficile infection)
- NSAIDs (non-steroidal anti-inflammatory drugs, e.g. ibuprofen)
- Acid-suppressing agents (PPIs, magnesium-containing antacids)
- Cytostatic drugs (anti-cancer drugs)
- SSRIs (a class of antidepressants)
- Metformin and other oral blood glucose-lowering agents
If you suddenly develop diarrhoea after starting a new medicine, you should inform your doctor.
Underlying causes of digestive disorders
The most common digestive disorders underlying sudden diarrhoea are:
- Irritable bowel syndrome (IBS): It affects 10–15% of adults in North America. In the diarrhoea-predominant type (IBS-D), symptoms worsen after eating or as a result of stress.
- Inflammatory bowel disease (IBD): Crohn’s disease is characterised by recurrent, generally non-bloody diarrhoea, whilst ulcerative colitis causes bloody, mucous stools, cramps and an urgent need to pass stools. There are approximately 55,000 people living with IBD in Hungary.
- Microscopic colitis: It is characterised by watery, loose stools, the underlying cause of which can be determined by colonoscopy and histology. It mainly affects women around the age of 50.
- Coeliac disease (celiac disease): It is characterised by recurrent abdominal pain, bloating and greasy, foul-smelling stools. Its prevalence is approximately 1%.
- Small intestinal bacterial overgrowth (SIBO): It affects approximately 10% of the general population and 30–85% of those with IBS. It is characterised by bloating, abdominal pain and diarrhoea.
Classification by mechanism
From a medical perspective, sudden diarrhoea can be classified according to various physiological mechanisms:
| Type | Featured on | Example |
|---|---|---|
| Secretory | It doesn’t stop even when you’re starving | Cholera, VIPoma, microscopic colitis |
| Osmotic | It eases when you cough | Lactose intolerance, sorbitol intake |
| Inflammatory (bloody) | Bloody, mucous, feverish | IBD, infectious colitis, ischaemic colitis |
| Steatorrhoea | Greasy, smelly, bulky | Pancreatic insufficiency, coeliac disease, SIBO |
| Motility disorder | Bloating and cramps | IBS, hyperthyroidism |
When should you see a doctor straight away?
Most cases of mild diarrhoea clear up on their own within a few days without treatment. However, there are certain symptoms that require immediate medical attention:
- Bloody or dark stools – may be a sign of inflammatory bowel disease, infectious colitis or a malignant lesion
- A persistent fever of over 38.5 °C, which lasts for more than 48 hours
- More than 6 bowel movements a day
- Signs of severe dehydration: dry mouth, dark urine, dizziness, weakness
- Severe, cramp-like abdominal pain
- Unexplained weight loss in recent weeks
- A patient aged over 70 or a person with a weakened immune system (e.g. a cancer patient, or someone undergoing immunosuppressive treatment)
- Symptoms lasting longer than 3–4 days they do not improve even with treatment at home
How is sudden diarrhoea diagnosed?
The doctor makes a diagnosis based on the symptoms, medical history and the necessary tests.
Laboratory and stool tests
- Stool culture: Detection of Salmonella, Shigella and Campylobacter
- C. difficile toxin test: It is particularly important after taking antibiotics
- Search for parasites: Giardia, Cryptosporidium, Entamoeba
- Stool fat analysis: if malabsorption is suspected (abnormal: fat content exceeding 7 g per day)
- Blood count, CRP, sedimentation rate: to detect an inflammatory process
- Faecal calprotectin: a sensitive marker of inflammation, which correlates well with the severity of endoscopic findings
The role of endoscopy in the investigation of acute diarrhoea
In cases of chronic or recurrent sudden diarrhoea, a colonoscopy is an essential examination. It can be used to identify intestinal polyps, areas of inflammation, ulcers and neoplastic lesions. Biopsies can be taken to confirm or rule out microscopic colitis, IBD and other mucosal lesions – even if the endoscopic image appears normal.
Endomedix has specialist experience in gastroenterology and in investigating the causes of diarrhoea. The COLONOSCOPY UNDER ANAESTHESIA It is completely painless and carried out under propofol anaesthesia – the patient feels nothing and wakes up feeling refreshed after a short time. At Endomedix, based on professional judgement, we use only general anaesthesia, not sedation, to ensure the patient’s safety and maximum comfort.
Home and medical treatment options
Rehydration – the first and most important step
In the event of sudden diarrhoea, the body rapidly loses water and electrolytes (sodium, potassium, magnesium). Oral rehydration solutions – which contain glucose and electrolytes – enhance the intestine’s ability to absorb fluids and restore balance. In cases of severe dehydration, intravenous fluid replacement is required.
Dietary recommendations
- Avoid fatty, spicy foods and dairy products during the acute phase
- Eat easily digestible foods: boiled rice, toasted bread, boiled potatoes, bananas
- A lactose-free diet for those with lactase deficiency
- A gluten-free diet for coeliac disease
- A low-FODMAP diet for IBS: wheat, onions, garlic, certain fruits and dairy products should be avoided
Medication options
- Loperamide: symptomatic treatment, slows down bowel motility – not to be used in cases of bloody diarrhoea
- Rifaximin: in cases of bacterial overgrowth and IBS-D
- Cholestyramine: in cases of bile acid diarrhoea (e.g. following resection of the terminal ileum)
- Probiotics: may be effective in cases of IBS and antibiotic-associated diarrhoea, when used for up to 12 weeks
Important: Antibiotics are contraindicated in cases of EHEC (O157:H7 E. coli) infection, as they increase the risk of haemolytic uraemic syndrome (HUS). The decision on treatment should always be left to a doctor.
The role of Endomedix in the investigation of sudden diarrhoea
If sudden diarrhoea returns, lasts for more than three days, or is accompanied by other warning signs, do not delay seeking medical attention. The gastroenterologists at Endomedix will draw up a personalised examination plan and carry out the necessary procedures using state-of-the-art equipment, including high-resolution video endoscopes and carbon dioxide insufflation.
If, based on the symptoms, a colonoscopy is required, the COLONOSCOPY UNDER ANAESTHESIA ensures complete freedom from pain. If an examination of both the stomach and the large intestine is required, the GASTRIC AND COLONOSCOPY UNDER ANAESTHESIA It can only be carried out once. Not sure which test is right for you? Book an appointment for a specialist gastroenterology consultation, where a specialist will assess your symptoms in person and determine the next steps.
How can you prevent sudden diarrhoea?
- Regular and thorough hand washing, especially before eating and after using the toilet
- Proper food handling and storage (heat treatment, maintaining the cold chain)
- Consumption of pasteurised dairy products and bottled water whilst travelling
- Taking probiotics after a course of antibiotics, on the advice of a doctor
- Regular gastroenterological screening from the age of 50
When is medical treatment urgent, and when is it acceptable to wait?
A one-off episode of mild, short-lived diarrhoea does not usually require immediate medical attention. It is sufficient to ensure adequate fluid intake, follow a gentle diet and get plenty of rest.
You should see a doctor if:
- Are the stools bloody or black?
- It is accompanied by a high fever (above 38.5 °C)
- Severe abdominal cramps; vomiting is also present
- The symptoms last for more than 3–4 days
- Infants, young children, the elderly or people with weakened immune systems are affected
- The diarrhoea is recurrent and keeps coming back
Summary: Don’t ignore recurring diarrhoea
Sudden diarrhoea can be much more than just an inconvenience: it may be caused by an infection, a side effect of medication, a digestive disorder or a number of other factors. In some cases, the cause is a serious organic disease – such as inflammatory bowel disease, microscopic colitis, coeliac disease or even a cancerous lesion. These can only be diagnosed through appropriate specialist examination, including, where necessary, a colonoscopy and a biopsy.
If you’re unsure about your symptoms, don’t wait. Book an appointment at Endomedix for a consultation with a gastroenterologist, and find out what lies behind their complaints.
Frequently asked questions (FAQ)
How long can sudden diarrhoea last without treatment?
Acute infectious diarrhoea usually clears up on its own within 1–3 days. If the symptoms last for more than 3–4 days, you should see a doctor.
What foods can help with sudden diarrhoea?
The best choices during the acute phase are boiled rice, toasted bread, boiled potatoes and bananas. Avoid fatty, spicy foods, coffee, alcohol and dairy products whilst symptoms persist.
When should a colonoscopy be carried out in the event of sudden diarrhoea?
A colonoscopy is necessary if diarrhoea is recurrent, bloody and has persisted for three weeks or longer, or if it is accompanied by warning signs (weight loss, fever, anaemia). Routine screening is also recommended for people aged 50 and over.
Is general anaesthesia safer than sedation for a colonoscopy?
At Endomedix, propofol anaesthesia is administered and monitored throughout by an experienced anaesthetist. From a professional point of view, this is the safest and most comfortable option: the patient feels nothing and wakes up fully conscious within a short time.
How can IBS be distinguished from inflammatory bowel disease?
IBS can be diagnosed if there are no warning signs (bloody stools, weight loss, anaemia, night-time diarrhoea) and laboratory results are normal. In cases of inflammatory bowel disease, faecal calprotectin levels are elevated, and a colonoscopy plus histological examination is required for an accurate diagnosis.
Why does diarrhoea keep coming back?
Recurrent diarrhoea may be caused by IBS, microscopic colitis, IBD, coeliac disease, lactose intolerance, SIBO or food intolerance. Only a specialist examination can provide a more precise answer.
