Acute diarrhoea or gastroenteritis is the passage of loose stools more frequently than what is normal for that individual. This increased frequency is often associated with stools that are watery or semisolid, abdominal cramps and bloating.

Acute watery diarrhoea is an extremely common problem, and can be fatal due to severe dehydration, in both adults and children, especially in the very young and the old or in those who have poor immunity such as individuals with HIV infection or patients who are using certain medications that suppress the immune system.

In healthy adults, however, it is often no more than a nuisance. Because it may interfere with ones ability to work, it can also adversely affect the individual's income.

Acute diarrhoea is most often due to an infection. Bacteria such as E. coli and Vibrio cholerae, certain viruses and parasites such as Giardia can cause diarrhoea and vomiting. Certain medications and allergies to certain food ingredients are some non-infectious causes of acute gastroenteritis.

Diarrhoea is the most troublesome symptom and may be associated with nausea and vomiting. The frequency of stools varies depending on the cause and the severity of the illness. It is usually also associated with abdominal cramps, and symptoms of gas. When the vomiting and diarrhoea are severe it is not uncommon for the individual with the illness to get dehydrated and this in turn may lead to light-headedness, weakness, confusion, kidney failure and even death.

When acute diarrhoea is due to an infectious agent, it is usually not necessary to find out the cause, because the diarrhoea is self-limiting and often resolves in the majority of patients within a few days. If the diarrhoea becomes chronic (more than two weeks) then special tests may be necessary. For non-infectious causes of acute diarrhoea it is important to find the underlying cause so that the causative agent can be appropriately treated or eliminated.

It is important to remember that acute gastroenteritis is an illness that lasts only a few days and does not, in general, require antibiotic or anti-microbial treatment. Correcting water and electrolytes deficits that occur, because they are lost in the stools and vomitus, is best done with an oral rehydration solution. This is a solution made up of glucose and electrolytes such as sodium, potassium and bicarbonate. This solution should be given to all patients who can take fluids by mouth including those who are vomiting. Usually enough water and electrolytes are absorbed to prevent the patient becoming dehydrated despite the vomiting. One can buy packets of oral rehydration salts, which are dissolved in safe drinking water. A simple and effective solution can be made cheaply and easily at home by adding one flat teaspoon of sugar, one-eighth tip of a teaspoon of salt to eight ounces (240 ml/glass) of water. It is important that this solution be drunk frequently to ensure that the patient does not get dehydrated.

Medicines to decrease the diarrhoea and vomiting may be used when symptoms are severe. Food can be given with no restrictions as soon as the patient is able to eat without discomfort. It is a common misconception that foods worsen diarrhoea but this has not been shown to be the case in carefully done studies.

Admission to a hospital for intravenous fluids may be necessary if dehydration occurs despite drinking the oral rehydration solution.

Since most cases of acute watery diarrhoea are infectious, especially in developing countries, the majority of such illnesses can be prevented by drinking water or eating foods that are not contaminated with infectious agents. Washing hands frequently with non-contaminated water, when caring for a patient with diarrhoea as also always before eating is important. Proper storage of food and water is also important to prevent harmful bacteria from contaminating them.