Acute Diarrhea and Enterocolitis

Acute diarrhoea is the abrupt onset of increased stool frequency or decreased stool consistency lasting less than about two weeks, most often caused by infection of the small or large intestine (enterocolitis). It is among the most common acute illnesses worldwide and ranges from self-limited watery diarrhoea to inflammatory, sometimes bloody, disease.

Definition

Acute diarrhoea is the passage of three or more loose or watery stools per day, or an increase over an individual's baseline, with onset within the preceding roughly two weeks; enterocolitis denotes inflammation of the small and large intestine that commonly underlies the infectious forms.

Scope

The entry covers the definition, mechanisms, and main categories of acute diarrhoea and infectious enterocolitis, their epidemiology, and the broad evidence base, as a reference topic. It does not provide antibiotic selection, rehydration prescriptions, or other individualised management, which are set by current clinical guidelines.

Core questions

• How is acute diarrhoea defined and distinguished from chronic diarrhoea by duration?
• What distinguishes secretory/non-inflammatory (watery) from inflammatory diarrhoea?
• Which pathogens and mechanisms most commonly cause acute infectious enterocolitis?
• What features mark more severe or invasive disease that warrants closer evaluation?

Key concepts

• Acute versus chronic diarrhoea (duration)
• Non-inflammatory (watery) diarrhoea
• Inflammatory (dysenteric) diarrhoea
• Secretory versus osmotic mechanisms
• Infectious enterocolitis
• Toxin-mediated diarrhoea
• Clostridioides difficile infection
• Dehydration and fluid-electrolyte loss

Mechanisms

Acute diarrhoea results when intestinal fluid secretion exceeds absorption or when transit and mucosal function are disturbed. Non-inflammatory diarrhoea is typically watery and secretory, often driven by enterotoxins or viruses acting mainly on the small bowel without much tissue damage; inflammatory diarrhoea involves invasion or cytotoxin-mediated damage of the colonic and ileal mucosa, producing fever, abdominal pain, and blood or leukocytes in the stool. Many cases are infectious, caused by viruses, bacteria, or protozoa, and some follow antibiotic exposure as Clostridioides difficile colitis. The principal acute danger is loss of fluid and electrolytes leading to dehydration.

Clinical relevance

Acute diarrhoea is an extremely common reason for medical contact and a major cause of dehydration, and recognising the distinction between non-inflammatory and inflammatory patterns frames how clinicians approach evaluation and the rationale for stool testing. This entry presents these concepts for reference and education and does not provide treatment, antimicrobial, or rehydration recommendations, which depend on individualised assessment and current guidelines.

Epidemiology

Acute diarrhoeal illness is among the most frequent acute conditions globally, with a very large annual burden and a leading cause of morbidity and, in resource-limited settings and young children, of mortality, largely through dehydration. It is also the dominant syndrome of travellers' diarrhoea and of foodborne and waterborne outbreaks.

Evidence & guidelines

Professional society guidelines address the diagnosis, treatment, and prevention of acute diarrhoeal infections in adults and the management of specific causes such as Clostridioides difficile; specific recommendations evolve and should be taken from the current versions rather than from this overview.

History

Acute diarrhoea has been a major cause of human illness throughout history, and nineteenth-century work on cholera linked it to contaminated water and to a secretory mechanism. Twentieth-century microbiology identified the bacterial, viral, and protozoal agents of enterocolitis and clarified toxin- and invasion-mediated mechanisms, while oral rehydration therapy became a landmark advance in countering its principal danger, dehydration.

Key figures

• Herbert L. DuPont
• Mark S. Riddle
• J. Thomas LaMont

Seminal works

• dupont-2014
• riddle-2016

Frequently asked questions

When is diarrhoea considered acute rather than chronic?

Diarrhoea is generally termed acute when it lasts less than about two weeks; persistent diarrhoea spans roughly two to four weeks, and chronic diarrhoea lasts beyond about four weeks, a distinction that helps frame the likely causes and evaluation.

What is the most important early concern in acute diarrhoea?

Loss of fluid and electrolytes leading to dehydration is the principal early danger, especially in young children and older or frail adults; assessing and addressing hydration is central, with specific management guided by clinical guidelines.