Diarrhea: overview, causes, symptoms, treatment and prevention

Classification according to duration

According to the duration of the diarrhoea, an acute diarrhoea can be distinguished from a chronic diarrhoea. Acute diarrhoea lasts a maximum of two to three weeks and usually has infectious or toxic causes. Longer lasting diarrhoea is called chronic diarrhoea, for which many causes such as food intolerances, chronic intestinal diseases or tumours are possible.

Classification according to the origin of the disease

Diarrhea can be further differentiated according to the pathomechanism, that is, how the disease develops. The diseases and mechanisms are explained in detail under "Causes".

Forms of diarrhoea can also be usefully classified according to the cause. Infections and food intolerances usually lead to acute diarrhoea, while chronic intestinal diseases, diseases of the exocrine pancreas and carcinomas are examples of the causes of chronic diarrhoea.

Infections

The most common triggers of diarrhoea are bacteria and viruses that lead to gastroenteritis. The most important germ worldwide is the cholera pathogen, Vibrio cholerae, which affects around six million people worldwide and kills over 100,000. In Germany, however, cholera is extremely rare; here, infections are often caused by human noroviruses and human rotaviruses or salmonellae. Diarrhoea is also often caused by spoiled food: the triggers here are toxins produced by bacteria (see below: "Food poisoning").

In Germany, there is an obligation to report many diarrhoeal pathogens. In 30 to 50 % of all travellers to (sub)tropical countries, travellers' diarrhoea of varying severity develops. The most important protective measure against all forms of infectious diarrhoea is personal hygiene and the consumption of uncontaminated water and food.

In diarrheal diseases caused by bacteria, a distinction is made between three mechanisms:

• Secretion-type pathogens are, for example, Vibrio cholerae or ETEC (enterotoxic E. coli, the main pathogen of traveler's diarrhea). They act on the intestinal mucosa and cause it to release electrolytes and water into the intestine.
• Representatives of the invasion type are, for example, Shigella, Campylobacter, Clostridioides difficile (antibiotic-associated colitis, see also under drugs) or EIEC/EHEC (enteroinvasive or enterohaemorrhagic E. coli). These invade the mucosal cells of the intestine, multiply there and lead to the destruction of the cells.
• Pathogens of the penetration type are Salmonella and Yersinia. These are absorbed by the intestinal mucosa and transported into the connective tissue below, where they cause an inflammatory reaction. How this leads to diarrhoea has not yet been clarified exactly.

Very often diarrhea is also caused by viruses. The main representatives of these viruses are human rotaviruses and human noroviruses. In (sub)tropical countries, intestinal parasitosis also plays an important role in diarrhoeal diseases, even more so than in northern countries.

Food intolerances

Food poisoning leads to diarrhea because bacteria were able to multiply in the spoiled food and form toxins called enterotoxins. Representatives of these bacteria are Staphylococcus aureus, Clostridium perfringens and Bacillus cereus. The multiplication of the bacteria is favoured by insufficient hygiene during preparation and too warm storage. The actual trigger of diarrhoea is therefore not the bacteria themselves, but the ingestion of the enterotoxins already formed. Since the enterotoxins of Staphylococcus aureus, for example, are very stable to heat, even cooking already spoiled food does not protect it.

Lactose intolerance is also frequently encountered. In Germany, about 15% of the population is affected, in Asian ethnic groups over 95%. Depending on the severity of the intolerance, flatulence, diarrhoea and abdominal pain occur. In the intestine, milk sugar (lactose) can be broken down by the enzyme lactase to the simple sugars glucose and galactose. In the case of lactose intolerance - which is the normal case for the majority of the world's adult population - this enzyme is completely or partially absent, so that lactose is broken down by bacteria in the large intestine. This produces the gases carbon dioxide and hydrogen and short-chain fatty acids, which are osmotically active, i.e. attract water, and thus trigger diarrhoea. With the lactose breath test, this cause can be clarified relatively easily.

Another form of food intolerance is food allergies, e.g. to strawberries, milk, nuts, egg whites or fish.

Drugs

Taking antibiotics can lead to diarrhea because they not only act on bacterial pathogens but also damage the bacteria of the physiological intestinal flora. The spectrum of antibiotic-associated diarrhea ranges from only a little, softened stool to Clostridioides difficile-associated diarrhea with the serious complication of pseudomembranous colitis.

Of course, the use and abuse of laxative medications, known as laxatives, can also lead to diarrhea. In particular, the abuse of laxatives with the aim of weight loss leads to electrolyte losses, which in turn can lead to constipation or, in extreme cases, to life-threatening cardiac arrhythmias.

Diarrhoea is also a possible side effect of some other medicines, for example cancer drugs (cytostatics) and iron preparations, or food supplements such as vitamin C (ascorbic acid). Excessive consumption of the sugar substitute sorbitol (e.g. in chewing gum) also has a laxative effect.

Malassimilation Syndromes

The "poor utilization" of nutrients is called "malassimilation". A further distinction is made between diseases in which food is not "broken down" properly (maldigestion) and diseases in which the absorption of the broken-down food components is disturbed (malabsorption).

Maldigestion is caused by surgical removal of the stomach (gastrectomy), an inadequately functioning pancreas (exocrine pancreatic insufficiency), loss of bile acids or obstruction of the bile ducts. All these diseases have in common that the digestive enzymes necessary to break down the food supplied do not arrive in the intestine or are not produced at all, or not in sufficient quantity.

In malabsorption, the nutrients are not absorbed by the intestinal mucosa. This is the case, for example, in indigenous sprue (gluten intolerance), Whipple's disease, amyloidosis or after removal of the small intestine.

Other causes

• Poisoning (intoxication) with, for example, arsenic, mercury, alcohol or fungi
• Chronic inflammatory bowel diseases. In Crohn's disease, diarrhea is typically without blood, whereas in ulcerative colitis it is bloody and mucous.
• hormonal (endocrine) diseases (e.g. hyperthyroidism)
• Allergy (Idiosyncrasy)
• Psychological triggers (e.g. stress, anxiety)
• Irritable Bowel Syndrome