What infectious agents cause foul‑smelling, pale (clay‑colored) stool in children?

Infectious Causes of Malodorous Pale Stool in Children

Giardia lamblia is the single most important infectious agent causing foul-smelling, pale (clay-colored) stool in children, producing characteristic explosive, watery, foul-smelling stools or semisolid stools with evidence of steatorrhea (fat malabsorption). 1

Primary Parasitic Pathogen

• Giardia lamblia (Giardia duodenalis) is the classic cause of malodorous pale stool in pediatric patients, presenting with explosive, watery, foul-smelling diarrhea or semisolid stools with visible fat (steatorrhea), flatulence, abdominal distention, and weight loss. 1

• Giardiasis causes steatorrhea (fat malabsorption) more frequently than other enteropathogens—in one pediatric study, 35.7% of children infected with Giardia demonstrated steatorrhea, compared to only 40% of bacterial infections showing occult blood. 2

• Children in day care settings are at particularly high risk for Giardia infection, as are those with immunodeficiency states (hypogammaglobulinemia, secretory IgA deficiency), gastrectomy, or achlorhydria. 1

• Diagnosis is established by examination of stool or duodenal fluid for cysts or trophozoites; multiple stool specimens may be needed as shedding can be intermittent. 1

Other Parasitic Causes

• Cryptosporidium species should be considered in children with persistent diarrhea (≥14 days), particularly in immunocompromised hosts, though pale stool is less characteristic than with Giardia. 3

• Cyclospora cayetanensis and Cystoisospora belli can cause persistent diarrhea with malabsorption but are less common in children and typically seen in immunocompromised patients or travelers. 3

Viral Pathogens (Less Common Presentation)

• Rotavirus is the most common viral cause of gastroenteritis in young children and can occasionally produce pale, watery stools due to temporary lactose malabsorption and fat malabsorption during acute infection, though foul odor is less prominent than with Giardia. 4

• Rotavirus was detected in 13.3% of diarrheic children in one study, and viral pathogens overall are more common in children <5 years old (38% vs 16% in older children). 2, 4

Bacterial Pathogens (Rare Cause of Pale Stool)

• Bacterial pathogens (Salmonella, Shigella, Campylobacter, STEC) typically cause bloody diarrhea rather than pale stool, though severe bacterial gastroenteritis can occasionally produce malabsorption with steatorrhea. 3

• Clostridium difficile was the most commonly detected pathogen (16%) in one pediatric diarrhea study but typically does not produce pale, malodorous stool—it more commonly causes watery or mucoid diarrhea. 4

Clinical Approach to Pale, Malodorous Stool

• Steatorrhea (fat in stool) is the hallmark of malabsorption and produces the characteristic pale, clay-colored, foul-smelling, greasy stool that floats. 2, 5

• Fat malabsorption occurs when there is insufficient pancreatic enzyme activity, insufficient bile acid, disease of the small intestinal wall (as with Giardia), or multiple defects. 5

• Children with diarrhea excrete significantly more lipids in feces than non-diarrheic children, and steatorrhea is most evident in protozoal infections, particularly Giardia. 2

• The acid steatocrit test can be used as a semi-quantitative laboratory tool to evaluate fat malabsorption in diarrheic children and detects 16.7% more fecal fat than traditional methods. 2

Diagnostic Testing

• Stool examination for ova and parasites (O&P) is essential when pale, foul-smelling stool suggests Giardia infection, though multiple specimens may be required. 1

• Stool testing for bacterial pathogens (Salmonella, Shigella, Campylobacter, Yersinia, STEC) should be performed when fever, bloody stools, or severe abdominal cramping are present, but these organisms rarely cause pale stool. 3

• A broader set of bacterial, viral, and parasitic agents should be considered in the context of a possible outbreak or in immunocompromised children with persistent diarrhea. 3

Common Pitfalls

• Do not assume pale stool is always due to biliary obstruction—in the setting of acute diarrhea with foul odor, Giardia infection is far more likely than hepatobiliary disease in children. 1

• Do not delay testing for Giardia in children with persistent diarrhea (≥14 days), weight loss, and steatorrhea, as chronic infection can lead to severe nutrient deficiencies. 1, 6

• Recognize that malabsorption of sugars, nitrogen, fats, and micronutrients accompanies diarrheal disease and poses a major threat if diarrhea becomes chronic or recurrent. 6