Diarrhea is defined as the passage of unformed or abnormally fluid stools at an increased frequency. Acute diarrhea has a duration of < 4 weeks and may be classified on the basis of etiology and presentation. On the basis of etiology, acute diarrhea may be classified into infectious and non-infectious sub-types. Based on the type of presentation, acute diarrhea may be classified into watery and inflammatory types. Watery diarrhea may be further classified into secretory and osmotic types of diarrhea.

• Acute diarrhea may be classified according to etiology into infectious and non-infectious subtypes/groups. The infectious group may further be classified into bacterial, viral, fungal and protozoal subgroups. The non-infectious group is further classified into diarrhea due to medications, poisoning and systemic illnesses.

• Based on the type of presentation, acute diarrhea may be classified into watery and inflammatory types. Watery diarrhea may further be classified into secretory and osmotic types of diarrhea.