Diarrhea for weeks: what causes persist past a virus, and what should you test?

Diarrhea for Weeks: What Causes Persistence Beyond a Virus—and What to Test

Diarrhea that lasts more than a few days often points to a simple viral infection. But when loose stools continue for weeks, it’s time to look beyond the ordinary. Persistent diarrhea can affect your nutrition, hydration and quality of life. Below, we explain common non-viral causes, the key tests to consider, and when to see a doctor.

Why Does Diarrhea Sometimes Last Weeks?
A typical “stomach bug” clears in a week. If diarrhea lingers, other processes may be at work:

• A brief infection can trigger ongoing gut sensitivity (postinfectious IBS).
• Inflammation, structural changes or malabsorption in the intestines may prevent normal digestion.
• Chronic infections, medications or systemic conditions can continually irritate your bowels.

Common Non-Viral Causes of Chronic Diarrhea

1. Postinfectious Irritable Bowel Syndrome (PI-IBS)

• Up to 10% of people develop IBS after a bout of gastroenteritis (Spiller, 2006).
• Symptoms include alternating diarrhea and constipation, crampy pain and urgency.
• No permanent damage on imaging, but heightened gut sensitivity persists.

2. Inflammatory Bowel Disease (IBD)

• Ulcerative colitis and Crohn’s disease can begin with persistent diarrhea, sometimes with blood or mucus.
• May be accompanied by weight loss, fatigue, fever or joint pain.
• Early diagnosis and treatment improve long-term outcomes.

3. Microscopic Colitis

• Causes watery diarrhea, mainly in people over 50.
• Colon appears normal on scope; diagnosis requires a tissue biopsy.
• Often linked to certain medications (NSAIDs, SSRIs) or autoimmune conditions.

4. Malabsorption Syndromes
   a. Celiac Disease

   • Immune reaction to gluten damages the small intestine, leading to fat-rich, foul-smelling stools.
   • Often accompanied by bloating, weight loss and nutrient deficiencies.
     b. Pancreatic Exocrine Insufficiency
   • Poor enzyme output causes fat malabsorption.
   • Common after pancreatitis or in cystic fibrosis.
     c. Bile Acid Diarrhea
   • Excess bile salts reaching the colon irritate the lining.
   • May occur after gallbladder removal or in Crohn’s affecting the terminal ileum.

5. Chronic Infections and Parasites

• Giardia lamblia, Cryptosporidium or Cyclospora can smolder for weeks, especially if your immune system is weakened.
• May cause weight loss, bloating and nutritional deficiencies.

6. Medications and Supplements

• Antibiotics (risk of C. difficile), magnesium-based antacids, metformin and certain cancer drugs can trigger long-term diarrhea.
• Review any new or ongoing medications with your provider.

7. Endocrine and Metabolic Causes

• Hyperthyroidism speeds up gut motility, causing loose stools.
• Diabetes can affect nerves in the gut (autonomic neuropathy), leading to diarrhea.

8. Liver Disease and Portal Hypertension

• Advanced cirrhosis may alter bile flow and gut permeability (D’Amico et al., 2006).
• Look for other signs: jaundice, fluid retention, easy bruising.

Key Tests and Diagnostic Approach
A stepwise evaluation helps pinpoint the cause of diarrhea for weeks. Not every test is needed for everyone; your doctor will tailor the workup based on your history and symptoms.

1. Basic Blood Work

• Complete blood count (CBC): checks for anemia or infection.
• C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR): markers of inflammation.
• Liver enzymes, albumin and electrolytes: assess nutrition, hydration and liver function.
• Thyroid-stimulating hormone (TSH): screens for hyperthyroidism.

2. Stool Studies

• Culture and sensitivity: looks for bacteria like Salmonella, Shigella or Campylobacter.
• Ova and parasite exam: Giardia, Cryptosporidium, Entamoeba histolytica.
• Clostridioides difficile toxin: especially if you’ve taken antibiotics.
• Fecal calprotectin or lactoferrin: elevated in inflammatory bowel disease.
• Fecal fat or elastase: detects fat malabsorption and pancreatic insufficiency.

3. Serologies and Breath Tests

• Tissue transglutaminase (tTG) antibodies: screens for celiac disease.
• Lactose hydrogen breath test: identifies lactose intolerance.
• Glucose or lactulose breath test: evaluates small intestinal bacterial overgrowth (SIBO).

4. Imaging and Endoscopy

• Colonoscopy with biopsies: essential for diagnosing IBD, microscopic colitis and colorectal cancer.
• Upper endoscopy with duodenal biopsies: confirms celiac disease or other small-bowel disorders.
• Abdominal CT or MRI: looks for structural problems, pancreatic disease or inflammatory changes.

5. Specialized Tests (as Indicated)

• SeHCAT scan (where available) for bile acid diarrhea.
• Stool elastase and lipase panels for pancreatic function.
• Capsule endoscopy or small bowel enterography for obscure small-intestine lesions.

When to Seek Help
If diarrhea lasts more than two weeks, or if you develop any of these “red flag” signs, talk to a healthcare provider promptly:

• Bloody stools or black, tarry stools
• High fever (over 101°F/38.3°C)
• Severe abdominal pain or distension
• Signs of dehydration (dizziness, dry mouth, dark urine)
• Unexplained weight loss over a few pounds
• Family history of colon cancer or IBD

You might start with a free online symptom check to get a sense of possible causes, but nothing replaces a thorough medical evaluation.

Managing Persistent Diarrhea at Home
While awaiting tests or appointments, try these supportive measures:

• Stay hydrated with electrolyte solutions, broths or oral rehydration salts.
• Eat small, frequent meals of bland foods (rice, bananas, toast).
• Avoid dairy, caffeine, alcohol and high-fat or very spicy foods.
• Consider a daily probiotic—some people find relief from Bifidobacterium or Lactobacillus strains.
• Review your medications with a pharmacist or doctor to rule out drug-induced diarrhea.

When to See a Doctor Immediately
If you experience any of the following, seek urgent care or call emergency services:

• Severe dehydration (inability to keep down fluids, very low urine output)
• Signs of shock (rapid heartbeat, fainting, confusion)
• Suspected toxic megacolon (profound abdominal pain, bloating, fever)

Speak to a doctor about anything that could be life-threatening or serious. Early diagnosis and treatment can prevent complications and get you back to feeling your best.

Take-Home Points
• Diarrhea lasting weeks is never “just a bug.”
• Causes range from postinfectious IBS to IBD, malabsorption, chronic infections and more.
• A targeted combination of blood tests, stool studies, breath tests and endoscopy guides diagnosis.
• Start with a free online symptom check if you’re unsure, but follow up with your healthcare provider.
• Seek immediate care for severe pain, bleeding or dehydration.

Persistent diarrhea can disrupt daily life and point to underlying issues that need attention. With the right tests and guidance, most causes are treatable or manageable. Don’t hesitate to get evaluated—you deserve relief and peace of mind.