Acute diarrhea in a child means looser or more liquid stools than usual, or more frequent stools — typically at least 3 in 24 hours — for less than 7 days, with or without fever or vomiting. During the first months of life the change in consistency is the more informative signal, because a young infant’s normal stool pattern varies considerably.
Acute gastroenteritis is the syndrome that usually travels with it: acute diarrhea with or without vomiting, fever or abdominal pain, generally of infectious origin. The two labels are used interchangeably in practice.
Most children in Europe with acute gastroenteritis have a mild, self-limited illness — one that settles on its own — and are managed at home with oral rehydration, drinking a solution of salts and glucose that replaces what the stools remove. The minority who deteriorate do so because losses continue faster than they are replaced. What changes management is therefore rarely which organism is responsible. It is how much fluid the child has already lost, how fast more is being lost, and whether the route of replacement should be oral, nasogastric (through a tube passed through the nose into the stomach) or intravenous.
Choose a route through this family
If the topic is new, start with why a child with diarrhea loses fluid and what causes the illness:
- Pathophysiology of Acute Diarrhea and Dehydration: how the intestine normally handles water, the osmotic and secretory mechanisms that interrupt it, and why children lose fluid faster than adults.
- Etiology and Risk Factors of Acute Diarrhea in Children: which organisms cause most childhood diarrhea in Europe, what their clinical patterns look like, and which children run a higher risk of severe dehydration.
Then comes the assessment of the child, and the tests that follow from it:
- Clinical Assessment of Acute Diarrhea and Dehydration: grading the severity of dehydration at the bedside, the signs that carry the most weight, and recognising hypernatremia before the laboratory result returns.
- Investigations in Acute Diarrhea and Dehydration: when a stool specimen is worth sending, why inflammatory markers cannot separate bacterial from viral, and when electrolytes or glucose change the plan.
Treatment follows in the order a child would receive it — admission and resuscitation, the fluid phases, then feeding and drugs:
- Admission and Shock Management in Acute Diarrhea: when a child should be admitted, when oral rehydration fails, and how shock is recognised and resuscitated.
- Rehydration Management in Acute Diarrhea: the order of the fluid phases, the arithmetic behind each volume, which solution belongs in which phase, and how fast sodium may be corrected.
- Refeeding and Drug Therapy in Acute Diarrhea: when and what to feed, why breastfeeding continues throughout, and where probiotics, racecadotril and antibiotics do and do not belong.
The last two turn to what can still go wrong, and to how the illness is prevented:
- Complications and Outcome of Acute Diarrhea and Dehydration: the usual course of the illness, the complications that change management, and which problems settle on their own.
- Prevention of Acute Diarrhea and Dehydration: rotavirus vaccination, hygiene in the household and in day care, breastfeeding, and the measures at home that keep a mild illness from becoming a severe one.
Where this topic stops
Acute diarrhea typically lasts less than 7 days and does not extend beyond 14 days. Beyond that boundary the problem is different and so is the differential. Malabsorption such as celiac disease, cow’s-milk protein allergy, inflammatory bowel disease and congenital transport defects are among the categories considered, and none of them is settled by rehydrating the child. Persistent diarrhea is a separate workup and is deliberately out of scope here.