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Definition of the Complaint

Diarrhea is one of the most common conditions for which patients seek medical care. It is a condition that continues to be associated with significant morbidity and mortality worldwide, despite medical advances. It is characterized by an increase in the frequency, volume, or liquid content of stool as compared to any given individual’s usual pattern.

Diarrhea may also be further characterized by the duration of the symptoms, with acute episodes of diarrhea generally resolving within 2 weeks, while chronic diarrhea generally lasts longer than 2 weeks. Another important distinction in the type of diarrhea is based on whether it is secretory or osmotic in nature. Agents that disrupt the normal absorption of intestinal luminal fluid at the cellular level generally cause a profuse and voluminous secretory diarrhea that continues regardless of the patient’s oral intake. Osmotic diarrhea, however, is the result of poorly absorbed substances that draw fluid into the intestinal lumen. This type of diarrhea tends to improve with fasting on the part of the patient.

The most common causes of diarrhea are infectious, with viral etiologies occurring more frequently than bacterial. The differential diagnosis of diarrhea, however, is quite extensive and includes some rare causes. Many cases of diarrhea occur in children who are otherwise well appearing, while some cases of diarrhea present in children who are ill appearing, due to either poor nutrition, hydration, or other systemic reasons.

Complaint by Cause and Frequency

There are myriad causes of diarrhea that can be stratified by age (Table 17-1) or diagnostic category (Table 17-2).

Table 17-1. Causes of Diarrhea by Age.
Table 17-2. Causes of Diarrhea by Diagnostic Category.

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