Common Causes of Diarrhoea
1. Viral Gastroenteritis
The most common cause of acute diarrhoea worldwide. Caused by norovirus, rotavirus, adenovirus and others. Usually lasts 1–3 days. Oral rehydration is the primary treatment; antibiotics are not needed.
2. Bacterial Food Poisoning
Salmonella, Staphylococcus, Campylobacter, Shigella, E. coli and other bacteria cause diarrhoea (sometimes with blood), vomiting and fever from contaminated food or water. More likely to require specific treatment.
3. Enteric Fever (Typhoid)
Salmonella typhi causes high fever, abdominal pain, headache and loose stools. Stool culture, blood culture and Widal test (with limitations) may be used in evaluation.
4. Parasitic Infections
Giardia lamblia, Entamoeba histolytica, Cryptosporidium and other parasites can cause prolonged diarrhoea, particularly with travel, contaminated water or immunocompromise.
5. Irritable Bowel Syndrome (IBS)
A functional bowel disorder causing alternating diarrhoea and constipation, cramping abdominal pain relieved by defecation and bloating. No structural abnormality is found. Diagnosis is clinical.
6. Inflammatory Bowel Disease (IBD)
Crohn's disease and ulcerative colitis cause chronic relapsing diarrhoea, often with blood, abdominal pain, weight loss and fatigue. Calprotectin and colonoscopy are key in evaluation.
7. Lactose Intolerance
Difficulty digesting lactose causes loose stools, bloating and cramping after milk or dairy products. Common in adults, particularly in certain ethnic groups.
8. Coeliac Disease
Gluten intolerance causes chronic diarrhoea (often fatty/bulky stools), weight loss, abdominal bloating and nutritional deficiencies. Anti-tTG IgA antibody is the initial blood test.
9. Medications
Antibiotics (especially broad-spectrum), metformin, NSAIDs, laxatives and many other medications can cause diarrhoea. Antibiotic-associated diarrhoea from Clostridioides difficile can be serious.
10. Traveller's Diarrhoea
Diarrhoea developing during or after international travel, particularly to regions with different sanitation. Often bacterial or parasitic in origin.
⚠️ When Should You Seek Medical Care?
Seek urgent medical attention if you experience any of the following:
- 🚨 Bloody diarrhoea or black tarry stools
- 🚨 Severe dehydration: very little urine, sunken eyes, extreme weakness, rapid heart rate
- 🚨 High fever with severe diarrhoea
- 🚨 Diarrhoea with severe abdominal pain
- 🚨 Diarrhoea in young children or elderly patients that is persistent
- 🚨 Diarrhoea after antibiotic treatment (possible C. difficile)
- Diarrhoea persisting more than 2 weeks without explanation
- Diarrhoea with significant unintentional weight loss
- Chronic diarrhoea with nutritional deficiency symptoms
Which Laboratory Tests May Be Considered?
Clinical note: Laboratory tests should be selected by a doctor based on your symptoms, history and clinical examination. Not every person requires all of the tests listed below.
| Test | Why a Doctor May Consider It |
|---|---|
| Stool Routine Examination | To assess for blood, pus, parasites and WBCs |
| Stool Culture | When bacterial infection is suspected (high fever, bloody stool) |
| Stool for Ova & Parasites | For suspected parasitic infection or prolonged diarrhoea |
| CBC | To assess for infection, anaemia, or eosinophilia (parasites) |
| CRP / ESR | Inflammatory markers — elevated in IBD, bacterial infection |
| Stool Calprotectin | Marker of intestinal inflammation — elevated in IBD, not IBS |
| Electrolytes | To assess dehydration and electrolyte loss from diarrhoea |
| Anti-tTG IgA | For suspected coeliac disease — initial serological test |
| Kidney Function Tests | When dehydration is significant |
Frequently Asked Questions
When does diarrhoea need a doctor?
Seek medical attention if diarrhoea lasts more than 2 days without improvement, is accompanied by blood, involves significant dehydration, comes with high fever or severe abdominal pain, or occurs in an elderly or immunocompromised patient.
Is oral rehydration solution (ORS) important?
Yes. The biggest risk with acute diarrhoea is dehydration. Oral rehydration with ORS is the primary treatment for most cases of gastroenteritis, regardless of whether an antibiotic is used.
Does diarrhoea always need antibiotics?
No. Most acute diarrhoea from viral causes does not benefit from antibiotics. Targeted antibiotic treatment may be appropriate for confirmed or strongly suspected bacterial infections based on clinical assessment.
QXL Diagnostic Support
QXL Diagnostics provides stool examinations, stool culture, stool calprotectin, blood tests and coeliac serology with home sample collection across Bengaluru.
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Medical Review
Medically reviewed by: Dr. Shantakumar Muruda, MD - Medical Biochemistry; Founder & CEO, QXL Diagnostics Super Speciality Lab, Bengaluru
Last medically reviewed: 2026-09-11
Clinical reference framework:Harrison's Principles of Internal Medicine; Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics; and relevant specialty guidance as clinically appropriate.
Medical Disclaimer: This information is intended for general health education and does not diagnose an individual medical condition. It does not replace consultation, diagnosis or treatment by a qualified healthcare professional. Seek urgent medical attention for severe, sudden or rapidly worsening symptoms or any emergency warning signs described above.