Diarrhea

What diarrhea is

Diarrhea is loose or frequent stool, usually three or more times a day. For the patient, what matters is the change from his or her usual pattern. It is not a disease in itself but a symptom with many possible causes: from a simple temporary infection to a chronic bowel disease. By duration, the types are:

• acute: less than 14 days (the most common form);
• persistent: from 14 days to 4 weeks;
• chronic: more than 4 weeks.

This distinction has practical importance: acute diarrhea is usually infectious and self-limiting; chronic diarrhea always calls for a more careful search for the cause.

Causes

Acute diarrhea is most often caused by infections: viruses (norovirus, rotavirus), bacteria (Campylobacter, Salmonella, Shigella, some types of E. coli) or parasites such as Giardia. It spreads through contaminated food or water, contact with sick people and poor hand hygiene; it is common during travel (traveler’s diarrhea).

Prolonged or chronic diarrhea may be related to:

• medicines, especially antibiotics (with a risk of Clostridioides difficile infection), metformin, magnesium, some blood pressure drugs;
• lactose intolerance or celiac disease;
• inflammatory bowel disease (ulcerative colitis, Crohn disease) or microscopic colitis;
• irritable bowel syndrome (IBS-D);
• malabsorption, pancreatic enzyme deficiency, hyperthyroidism;
• in people with a weakened immune system, opportunistic infections;
• more rarely, tumors or “overflow” diarrhea with partial blockage (hard stool stuck inside).

Dehydration: the main risk

With diarrhea, water and salts (electrolytes) are lost. Signs of dehydration are:

• thirst and a dry mouth;
• little urine or dark urine;
• weakness, dizziness, drowsiness;
• in children: sunken eyes, no tears, dry diapers for many hours.

Infants, older adults and people with chronic disease become dehydrated faster and with more serious consequences. In patients with heart or kidney disease who take diuretics, dehydration can cause a fall in blood pressure and kidney injury, so they should contact their doctor earlier.

When to see a doctor

Seek medical assessment if the diarrhea:

• lasts several days without improvement or keeps recurring;
• comes with blood, high fever or weight loss;
• started during or after a course of antibiotics;
• wakes you at night;
• occurs in infants, older adults or people with chronic disease, a weakened immune system or after a hospital stay.

How the diagnosis is made

The doctor asks about duration, medicines, recent travel, suspicious food and accompanying symptoms. Most acute episodes need no tests. As appropriate, the following may be needed:

• stool culture or tests for specific pathogens and parasites, when the diarrhea is severe, bloody or prolonged;
• blood tests (blood count, electrolytes, kidney function, CRP, TSH, tests for celiac disease);
• fecal calprotectin, a marker of bowel inflammation that helps tell inflammatory bowel disease from IBS;
• in chronic diarrhea or with alarm features, colonoscopy with biopsies, even when the lining looks normal, because some causes (such as microscopic colitis) are found only on biopsy.

How it is treated

• Rehydration is the basis. Drink fluids in small amounts and often. Oral rehydration solutions (ORS), sold in pharmacies, are the best choice; prepare them exactly as the package directs.
• Keep eating according to appetite. Infants continue breast milk or their usual formula. Avoid alcohol and very fatty or very sweet foods for a few days.
• Antibiotics are not needed for most acute diarrhea and may make things worse; they are given only when the doctor identifies a cause that requires them.
• Antidiarrheals such as loperamide can be used by adults for simple diarrhea, but not when there is blood in the stool, high fever or suspicion of severe infection, and not in young children without advice.
• Chronic diarrhea is treated according to the cause found: lactose-free diet, gluten-free diet (only after celiac disease is diagnosed), medicines for inflammatory disease, treatment of IBS-D and so on.

Hand washing with soap, correct food storage and clean water prevent most infectious diarrhea.