# Acute and Chronic Diarrhea in Children

## Overview

Diarrhea remains a leading cause of morbidity in children worldwide and one of the top reasons for pediatric outpatient and emergency department visits in developed countries. Acute diarrhea is defined as three or more loose or watery stools per day lasting fewer than 14 days. Persistent diarrhea spans 14-30 days, while chronic diarrhea exceeds 30 days. The vast majority of acute diarrhea in children is viral, self-limited, and managed with oral rehydration therapy (ORT). Dehydration assessment and fluid management are the most critical clinical skills in this setting.

## Acute Diarrhea

### Viral Gastroenteritis

Rotavirus was historically the most common cause of severe dehydrating diarrhea in young children, but its incidence has been dramatically reduced by vaccination. Norovirus is now the leading cause of acute gastroenteritis in children in the post-rotavirus vaccine era and is highly contagious, causing community and institutional outbreaks. Adenovirus (types 40 and 41) can cause prolonged diarrhea lasting up to 10-14 days. Astrovirus and sapovirus typically cause milder illness.

### Bacterial Gastroenteritis

Salmonella is a foodborne pathogen that causes bloody or non-bloody diarrhea, with bacteremia risk particularly in infants younger than 3 months and immunocompromised patients. Importantly, uncomplicated non-typhoidal salmonella in healthy children older than 3 months should not be treated with antibiotics, as this prolongs the carrier state. Shigella produces bloody diarrhea with high fevers and tenesmus, and seizures may actually precede the onset of diarrhea; treatment is with azithromycin. Campylobacter causes watery diarrhea that may become bloody and is associated with Guillain-Barre syndrome; early treatment with azithromycin is recommended. Shiga toxin-producing E. coli (STEC, including O157:H7) causes bloody diarrhea with risk of hemolytic uremic syndrome, and antibiotics must be avoided because they may increase HUS risk. Clostridioides difficile is increasingly recognized in children and is associated with antibiotic exposure. Testing is not recommended in children younger than 2 years due to a high rate of asymptomatic carriage. Treatment, when indicated, is oral vancomycin or fidaxomicin.

### Parasitic

Giardia lamblia causes watery, foul-smelling diarrhea with bloating and flatulence, often in daycare outbreaks, and is treated with metronidazole or tinidazole. Cryptosporidium causes watery diarrhea that is self-limited in immunocompetent children but can be severe in immunocompromised patients.

<image>Comparison table of common causes of acute diarrhea in children showing pathogen, transmission route, stool characteristics (watery vs. bloody), key clinical features, and antibiotic treatment recommendations for viral (rotavirus, norovirus), bacterial (Salmonella, Shigella, STEC, C. difficile), and parasitic (Giardia, Cryptosporidium) etiologies</image>

## Dehydration Assessment and Oral Rehydration Therapy

### Clinical Dehydration Assessment

| Feature | Minimal (<3%) | Mild-Moderate (3-6%) | Severe (>6-9%) |
|---------|---------------|---------------------|----------------|
| Mental status | Normal | Normal to listless | Lethargic/obtunded |
| Heart rate | Normal | Tachycardia | Tachycardia/bradycardia |
| Blood pressure | Normal | Normal | Hypotension |
| Eyes | Normal | Mildly sunken | Markedly sunken |
| Tears | Present | Decreased | Absent |
| Mucous membranes | Moist | Dry | Parched |
| Skin turgor | Normal | Decreased | Tenting |
| Capillary refill | Normal | 3-4 seconds | >4 seconds |
| Urine output | Normal | Decreased | Anuria |
| Management | ORT at home | ORT 50-100 mL/kg over 3-4 hr | IV 20 mL/kg NS bolus |

Dehydration severity is classified by clinical signs. Minimal or no dehydration (less than 3% body weight loss) presents with a normal exam and thirst. Mild-to-moderate dehydration (3-6%) is characterized by tachycardia, decreased urine output, dry mucous membranes, decreased tears, delayed capillary refill of 3-4 seconds, and mildly sunken eyes or fontanelle. Severe dehydration (greater than 6-9%) presents with hypotension, markedly sunken eyes and fontanelle, absent tears, tenting of skin turgor, altered mental status, and anuria.

### Oral Rehydration Therapy (ORT)

The WHO/UNICEF oral rehydration solution is a reduced osmolarity formula (245 mOsm/L) containing 75 mEq/L sodium and 75 mmol/L glucose. ORT is as effective as IV rehydration for mild-to-moderate dehydration and is the preferred method. The rehydration phase involves giving 50-100 mL/kg over 3-4 hours. Small, frequent volumes (5-10 mL every 5 minutes by syringe or spoon) minimize vomiting. If the child vomits, wait 20-30 minutes and restart. For maintenance, replace ongoing losses with 10 mL/kg per diarrheal stool and 2 mL/kg per episode of emesis. Age-appropriate diet should resume early, as continued feeding reduces the duration of diarrhea. Juice, soda, and sports drinks should be avoided because their high osmolarity and low sodium content can worsen diarrhea.

### IV Rehydration Indications

Intravenous rehydration is indicated for severe dehydration with hemodynamic compromise, failure of oral rehydration therapy (intractable vomiting or refusal to drink), altered mental status, suspected surgical abdomen, and ileus.

### Ondansetron for Vomiting

A single dose of ondansetron (0.15 mg/kg, maximum 4 mg) reduces vomiting, facilitates oral rehydration, and may reduce both IV fluid administration and hospitalization rates. It is generally well tolerated, though it should be avoided in patients with prolonged QTc. Some controversy exists around its routine use: it may mask surgical pathology and can transiently increase diarrhea volume.

## Stool Studies: When and What to Order

Stool studies are not routinely indicated for uncomplicated acute watery diarrhea. Indications for testing include bloody diarrhea, high fever, severe or prolonged symptoms, immunocompromised status, recent travel, daycare outbreaks, and antibiotic exposure. Stool culture identifies bacterial pathogens such as Salmonella, Shigella, Campylobacter, and E. coli. Stool PCR panels (multiplex) are rapid and sensitive but may detect colonization rather than true infection, particularly for C. difficile and enteropathogenic E. coli. Ova and parasite examination is reserved for chronic or persistent diarrhea, travel history, or daycare exposure. Fecal leukocytes and lactoferrin suggest an inflammatory or invasive process but are nonspecific.

<image>Dehydration assessment scale for children showing clinical signs categorized by severity (minimal, mild-moderate, severe) including mental status, heart rate, skin turgor, mucous membranes, eyes, tears, urine output, and capillary refill, with corresponding fluid deficit percentages and rehydration approach (ORT vs IV)</image>

## Chronic Diarrhea in Children

### Toddler's Diarrhea (Functional Diarrhea)

Toddler's diarrhea is the most common cause of chronic diarrhea in children aged 1-5 years. Children pass 3-6 loose stools per day, often containing undigested food particles, with the first stool of the day typically being the largest and most formed. Growth and development are normal, and laboratory values are unremarkable. The condition is related to excessive juice or fluid intake, a low-fat diet, and high fructose consumption. Management consists of dietary modification (reducing juice, increasing fat and fiber) and parental reassurance.

### Celiac Disease

Celiac disease is an autoimmune enteropathy triggered by gluten (wheat, barley, rye) in genetically susceptible individuals carrying HLA-DQ2 or HLA-DQ8. It presents with chronic diarrhea, abdominal distension, failure to thrive, and iron deficiency anemia, though it may be asymptomatic. Screening is performed with tissue transglutaminase IgA (TTG-IgA) plus total IgA, since 2-3% of celiac patients are IgA-deficient and will have false-negative TTG-IgA results (use TTG-IgG or deamidated gliadin peptide IgG instead). Diagnosis is confirmed by duodenal biopsy showing villous atrophy, crypt hyperplasia, and increased intraepithelial lymphocytes according to the Marsh classification. ESPGHAN guidelines allow a biopsy-sparing diagnosis in children with TTG-IgA greater than 10 times the upper limit of normal, positive endomysial antibody, compatible HLA, and symptoms. Treatment is a strict lifelong gluten-free diet, with TTG-IgA monitoring for adherence.

### Inflammatory Bowel Disease (IBD)

IBD is covered in a dedicated seminar (Topic 29) but should be considered in any child with chronic bloody diarrhea, weight loss, growth failure, or perianal disease.

### Lactose Intolerance

Primary lactose intolerance from genetic decline in lactase activity is rare before age 5 in most populations. Secondary lactose intolerance is a temporary malabsorption following viral gastroenteritis or mucosal injury. Diagnosis is based on clinical improvement with lactose elimination, hydrogen breath testing, or stool reducing substances in young children. Treatment involves a lactose-free diet or lactase enzyme supplementation.

### Other Causes of Chronic Diarrhea

Food protein-induced enterocolitis syndrome (FPIES) typically occurs in infants, presenting with profuse vomiting 2-4 hours after exposure to a trigger protein (milk, soy, rice, oat) and can cause severe dehydration and shock. Eosinophilic GI disorders include eosinophilic esophagitis and gastroenteritis. Immunodeficiency should be considered in recurrent or severe infections. Short bowel syndrome is a post-surgical cause. Congenital diarrheas such as microvillus inclusion disease and tufting enteropathy are rare conditions causing intractable diarrhea from birth.

## Clinical Pearls

ORT is one of the most important medical advances of the 20th century, saving millions of lives globally each year. C. difficile testing should not be performed in children younger than 2 years because the high asymptomatic colonization rate makes positive results uninterpretable. In bloody diarrhea with suspected STEC, antibiotics must be avoided because they may increase HUS risk by enhancing Shiga toxin release. A child with chronic diarrhea but normal growth most likely has functional diarrhea (toddler's diarrhea), and extensive workup is rarely needed. Total IgA should always be checked when screening for celiac disease, since IgA-deficient patients will have false-negative TTG-IgA results. Ondansetron is a powerful tool in the emergency department to avoid unnecessary IV lines and admissions: a single oral dose can be practice-changing.

## Key Controversy: Ondansetron for Pediatric Gastroenteritis

Strong evidence supports single-dose ondansetron in reducing vomiting, improving ORT success, and decreasing ED revisits. The AAP does not have a formal guideline endorsing routine use, and practice remains variable. Concerns include possible QTc prolongation (low risk at a single oral dose), a transient increase in diarrhea frequency, and the potential masking of surgical conditions. Many experts recommend a selective approach: using ondansetron for moderate dehydration with active vomiting preventing ORT, rather than for all vomiting children. From a cost-effectiveness standpoint, generic ondansetron is inexpensive, and the orally dissolving tablet (ODT) formulation is easily administered.

<image>Diagnostic approach algorithm for chronic diarrhea in children, stratified by age group (infant, toddler, school-age, adolescent), showing key differentials at each age, initial workup (growth assessment, stool studies, celiac panel, fecal calprotectin), and indications for referral to pediatric gastroenterology</image>

## References
- Guarino A, et al. European Society for Pediatric Gastroenterology, Hepatology, and Nutrition/European Society for Pediatric Infectious Diseases Evidence-Based Guidelines for the Management of Acute Gastroenteritis in Children in Europe. J Pediatr Gastroenterol Nutr. 2014;59(1):132-152.
- King CK, et al. Managing Acute Gastroenteritis Among Children: Oral Rehydration, Maintenance, and Nutritional Therapy. MMWR Recomm Rep. 2003;52(RR-16):1-16.
- Freedman SB, et al. Oral Ondansetron for Gastroenteritis in a Pediatric Emergency Department. N Engl J Med. 2006;354(16):1698-1705.
- Husby S, et al. European Society Paediatric Gastroenterology, Hepatology and Nutrition Guidelines for Diagnosing Coeliac Disease 2020. J Pediatr Gastroenterol Nutr. 2020;70(1):141-156.
- McDonald LC, et al. Clinical Practice Guidelines for Clostridioides difficile Infection (IDSA/SHEA). Clin Infect Dis. 2018;66(7):e1-e48.