Acute diarrhea is diarrhea that lasts for a short time, usually less than 3 to 4 weeks. Chronic diarrhea is diarrhea that lasts for a long time, usually more than 3 to 4 weeks. The ICD-10 code for acute diarrhea is R19.7, which means diarrhea, unspecified. The ICD-10 code for chronic diarrhea is K52.9, which means noninfective gastroenteritis and colitis, unspecified. These codes are used when there is not enough information to assign a more specific code, or when the cause of diarrhea is unknown or irrelevant.