Family doctor



DIARRHOEA - a patient's guide


This is a common condition which is usually self limiting. A variety of causes are outlined in this article.


What is it?

Diarrhoea is a very common symptom with many possible causes. The term is used to describe an increase in frequency of bowel motions, or increased stool liquidity, or sometimes a sense of faecal urgency. A textbook definition of diarrhoea is: "the passage of greater than 300 ml of liquid faeces in 24 hours". However, this is not a very useful definition, as stool quantity is hardly ever measured.

Common causes

As mentioned above, the causes of diarrhoea are myriad. To determine which causes are more likely, a doctor will need to know, amongst other things, a patient's normal bowel habit, and how long the diarrhoea has been present. The more common causes are listed below:

1. Infections

The most common causes of acute diarrhoea are infectious agents (bacteria or viruses). In children, infectious diarrhoea is an important cause of severe illness and accounts for about 5 million deaths each year in children under the age of 5. The problem is particularly common in developing countries, where contributing factors include poor hygiene, ineffective sewage systems, poor nutrition and lack of education. In developed countries, acute infectious diarrhoea is common in children attending creche or day-care centres.

"Food poisoning" is a term often used to describe infectious diarrhoea. This occurs when bacteria are transmitted by the "faecal-oral" route: usually someone who has the infection, or is a carrier of the bacteria, gets it on his/her hands and then handles food that is eaten by someone else.

A bacterium called Campylobacter jejuni is the most common cause of food poisoning in New Zealand. Salmonella is another common cause of food poisoning and is commonly associated with improperly stored or undercooked chicken, beef or pork.

"Travellers' diarrhoea" is another infectious type of diarrhoea. It is frequently caused by exposure to unpurified water, in which case the bacteria most likely to be involved include: Giardia, Cryptosporidium and Entamoeba Histolytica (causing amoebic dysentery).

2. Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is another common cause of diarrhoea and can be very difficult to treat. The symptoms come on intermittently and typically occur over months or years. Classically, a person with IBS will have alternating constipation and diarrhoea, but the disease can also present with abdominal pain as a predominant feature together with intermittent constipation or diarrhoea.

There appear to be two underlying mechanisms that can cause the symptoms of IBS:

1) abnormal gut motility (the normal peristaltic movements of the intestine is impaired)

2) increased sensitivity to distention of the intestine.

The disease is four times as common in women than in men, and is often triggered or exacerbated by emotional stress. Treatment is aimed at altering gut motility; either by having a high-fibre diet, or with various medications.

3. Medications

Many medications have diarrhoea as a possible side effect. Antibiotics can cause diarrhoea, either as a direct effect on the intestine, or by allowing overgrowth of normal gut flora. Eating acidophyllus yogurt during a course of antibiotics may prevent this problem.

Occasionally, a person taking a prolonged course of antibiotics gets persistent diarrhoea even after stopping the antibiotics, in which case they might be infected with a bacteria called Clostridium Difficile, and may need to take another more specific antibiotic to treat the diarrhoea.

Overuse of laxatives can also cause diarrhoea.

4. Inflammatory Bowel Disease

Crohn's Disease and Ulcerative Colitis are inflammatory bowel diseases, which can cause chronic diarrhoea (often severe and containing blood or mucous) as well as a variety of other symptoms.

5. Other

"Overflow diarrhoea" can occur in people who are constipated for a prolonged period of time and may in fact cause faecal incontinence.

Emotional stress or anxiety can cause a diarrhoea, which is usually mild and self-limiting.

HIV can cause diarrhoea through a variety of infections.

Diagnostic tests

In over 90% of patients with acute diarrhoea, the disease will resolve within 5-7 days and specific diagnostic tests are not really necessary.

However, if there are other associated symptoms, or if the diarrhoea is persistent, the doctor may request certain tests. These may include: a stool sample to look for bacteria or parasites, blood tests, or in certain cases sigmoidoscopy (a procedure that entails passing a "scope" through the rectum to get a look at the intestine).


1) Rehydration

Most adults with diarrhoea will not become dehydrated provided they take in adequate fluids. Fluids containing carbohydrates and electrolytes (e.g. fruit juice, energy drinks, Gastrolyte) are preferable.

In more severe diarrhoea, especially in children, dehydration can occur quickly and admission to hospital for intravenous fluids may be necessary.

2) Diet

It is generally accepted that people with diarrhoea find it more comfortable to rest the bowel by avoiding high-fibre foods, fats, milk products, caffeine and alcohol, instead taking in frequent small helpings of light meals and fluids.

3) Antidiarrhoeal agents

Drugs like Immodium, Lomotil and Diastop should be used with caution. They are generally safe in cases of mild to moderate diarrhoea and can improve one's comfort, but they should be avoided in cases of bloody diarrhoea, or where diarrhoea is associated with high fever and systemic illness.

4) Antibiotics

The overwhelming majority of patients with diarrhoea will not need antibiotics. However, if there are symptoms or signs of a systemic illness and/or the symptoms are persisting, and particularly if bacteria are identified, then an antibiotic may be appropriate.


There are many possible causes of diarrhoea. Most commonly, it is a mild and self-limiting illness, but if symptoms are severe or persistent, one should seek help from a doctor as specific tests and/or treatment may be necessary.

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