What is Acute Diarrhea?
Acute diarrhea is an episode of diarrhea lasting less than 14 days, characterized by an increase in stool water content, volume, or frequency (typically ≥3 loose or liquid stools per day). 1, 2
Core Definition and Characteristics
Acute diarrhea represents a time-limited gastrointestinal disturbance with specific duration criteria that distinguish it from other diarrheal syndromes. The Infectious Diseases Society of America provides the authoritative classification framework based on duration: acute (<14 days), prolonged (7-13 days), persistent (14-29 days), and chronic (≥30 days). 2
Key Defining Features:
- Duration: Less than 14 days from onset 1, 2, 3
- Stool characteristics: Decreased consistency (soft or liquid) with increased frequency 1
- Epidemiological threshold: ≥3 loose or liquid stools per day is commonly used for research and surveillance purposes 2, 4
- Patient perspective: The most distressing features are urgency and loose stools, reflecting unpredictable manifestations 1
Clinical Presentation Subtypes
Acute diarrhea manifests in two primary clinical patterns that guide management decisions:
Acute Watery Diarrhea
- Loose or liquid stools without visible blood 2
- Most commonly viral in etiology (rotavirus accounts for one-fourth of childhood cases) 1
- Generally self-limited, lasting 5-10 days 5
Acute Bloody Diarrhea (Dysentery)
- Frequent scant stools with visible blood and mucus 2
- Always classified as severe disease requiring immediate evaluation 2
- Often accompanied by fever, severe abdominal cramping, and systemic illness 6
Associated Symptoms
Infectious diarrhea frequently presents with accompanying features beyond stool changes:
- Nausea and vomiting 1
- Abdominal cramps 1
- Fever (particularly with inflammatory/invasive pathogens) 1
- Signs of dehydration in severe cases 7
Common Etiologies
When extensive diagnostic techniques are employed, a causative agent can be identified in 60-80% of acute diarrhea cases (compared to only 15-20% in the 1970s). 1
Viral causes (most common overall):
- Rotavirus (most common in children) 1
- Norwalk-like viruses, enteric adenoviruses, astroviruses, caliciviruses 1
Bacterial pathogens:
- Salmonella, Shigella, Yersinia, Campylobacter, pathogenic E. coli strains 1
Parasitic causes:
- Giardia, Cryptosporidium, Entamoeba histolytica 1
Clinical Significance
The most critical concern in acute diarrhea is fluid and electrolyte imbalance, particularly in vulnerable populations. 7 In the United States, children under 5 years experience 20-35 million episodes annually, resulting in over 200,000 hospitalizations and 325-425 deaths, with 65% of hospitalizations and 85% of deaths occurring in the first year of life. 1
High-Risk Populations Requiring Heightened Vigilance:
- Infants (especially <3 months) 7
- Elderly patients 1
- Immunocompromised individuals 1, 3
- Severely malnourished children 7
Important Clinical Pitfalls
Recent change in stool consistency is more diagnostically important than absolute frequency alone. 7 A patient's normal bowel pattern must be considered, as some individuals normally have more than 3 bowel movements daily.
In severely malnourished children, traditional dehydration assessment signs (sunken eyes and decreased skin turgor) are unreliable. 7 Alternative assessment methods must be employed in this population.
The presence of blood in stool always indicates severe disease requiring prompt evaluation for bacterial pathogens and consideration of antimicrobial therapy, whereas most watery diarrhea cases are viral and self-limited. 6