Definition:

Diarrhea is defined as the passage of loose or watery stools, typically at least three times in a 24-hour period [3]. Acute diarrhea is defined as diarrhea of ≤14 days in duration, in contrast to persistent (>14 days and ≤30 days) or chronic (>30 days) diarrhea. 

Types of Acute Diarrhea
Acute watery diarrhea Acute bloody diarrhea

In a non-epidemic situation, enterotoxigenic Escherichia coli (E. coli).
Epidemic disease; Vibrio cholera
seasonal out breaks: Norovirus, Campylobacter species, nontyphoidal Salmonellae, Aeromonas species, and enteroaggregative. 
E. coli, Giardia lamblia 

Shigella species, particularly Shigella flexneri, are the most important.
Other causes include Campylobacter jejuni, enteroinvasive and enterohemorrhagic E. coli, nontyphoidal Salmonella species, Entamoeba histolytica.