Causes of Diarrhea
In developing countries, diarrhea is almost universally infectious in origin.

There are many infections which can cause diarrhea. Among them are the viruses such as Rotavirus, Adenovirus, Norwalk virus etc. The Rotavirus is the most important cause of diarrhea in infants and children. Nearly all children are infected at least once before the age of two years, and repeat infections are common. It spreads from person to person especially if personal hygiene is not up to the mark.

In tropical areas, Rotavirus diarrhea occurs throughout the year. However, it is more frequent during the winter months. Bacteria such as shigella, salmonella, vibrio cholera also cause diarrhea. Cholera occurs in epidemics. Bacterial diarrheas peak is more common during the the rainy season.

Enterotoxigenic coli called ETT is an important cause of diarrhea. Parasites such as amoebiasis and giardiasis also can cause diarrhea, although not so commonly. Diarrhea is seen when an infant is teething. Irritation due to erupting teeth often leads to the infant putting his/her contaminated fingers into his/her mouth. In addition, there are many causes which could lead to diarrhea, such as malnutrition (which in effect sets up a vicious cycle and perpetuates malnutrition). It is more commonly seen when the infant is being weaned from breast feeding. Other causes are diseases such as sprue, celiac disease etc.

Most of the pathogenic organisms that cause diarrhea are transmitted primarily or exclusively by the fecal–oral route.