Diarrhea, Parasitic Evaluation

Diagnosis

Indications for Testing

• Diarrheal disease for >3-7 days and/or appropriate risk factors (eg, immunocompromised, foreign travel, drinking unpurified water)

Laboratory Testing

• Guide to confirming diagnosis in foodborne disease (CDC)
• Initial diagnostic approach – antigen testing to exclude most common parasites (Giardia duodenalis, Cryptosporidium spp, E. histolytica); test for persistent diarrhea (≥7 days) or known risk factors
  • Giardia duodenalis (synonyms Giardia lamblia, Giardia intestinalis)
    • Giardia stool antigen by EIA (preferred, most sensitive)
    • Repeat testing is recommended if initial test is negative and clinical suspicion is high
  • Cryptosporidium
    • Cryptosporidium spp stool antigen (EIA or DFA) preferred
    • Microscopic detection in stool requires special stains (eg, modified acid fast and multiple stool specimens); less sensitive than stool EIA
  • Entamoeba histolytica
    • Intestinal disease – Entamoeba stool antigen (EIA) is sensitive and specific
    • Extraintestinal disease (eg, liver abscess) – serologic testing preferred (Entamoeba histolytica antibody, IgG)
      • Stool antigen or ova and parasite exam are generally negative
  • Isospora belli
    • Microscopic examination of stool including special stain (eg, modified acid fast)
      • Oocytes appear red
  • Microsporidia
    • DFA stain – more sensitive and specific 
    • Ova and parasite examination with request for microsporidial stain – may require testing of multiple specimens
  • Strongyloides stercoralis
    • Serology is most sensitive; mild to moderate eosinophilia on CBC may be the only clue to parasitic infection if stools are negative
    • Ova and parasite examination with request for special stains
      • Ova and parasite exam may miss organisms in light infections; multiple specimens may be required
• If diarrhea persists >3 days, and if patient has defined risk factors or a negative antigen testing, consider serology testing and ova and parasite examination with special stains to detect less-common pathogens
  • Comprehensive stool ova and parasite examination of 3 specimens collected on separate days is recommended (including request for special stains) for the following
    • Patients with history of travel or residence in endemic area
    • Exposure history
    • Immunocompromised state
    • High pretest probability for parasitic infection
• Consider referral to a gastroenterologist for complete evaluation if infectious workup is negative and diarrhea persists

Differential Diagnosis

• Viral or bacterial diarrhea
• Primary or metastatic cancer
• VIPoma
• Mycobacterium tuberculosis
• Inflammatory bowel disease
• Irritable bowel syndrome
• Celiac disease

Clinical Background

Etiology of diarrhea may be infectious or noninfectious presenting with acute (<7 days) or chronic (>7 days) symptoms. Parasites are an infrequent or rare cause of acute diarrhea but a more common cause of chronic diarrhea.

• Acute diarrhea (acute gastroenteritis) – duration 1-7 days
  • Frequently infectious
  • May be foodborne, waterborne, or outbreak-associated
  • Most commonly caused by viruses and occasionally bacteria
  • Testing for gastrointestinal parasites generally not recommended for acute diarrheal episodes
• Chronic diarrhea – duration >7 days, often longer
  • More commonly noninfectious
  • Testing for parasites should be considered

Epidemiology

• Occurrence of parasite-associated disease
  • 5-15% in young children attending daycare
  • 1-2% in adults

Organism

• Giardia duodenalis (synonyms Giardia lamblia, Giardia intestinalis)

  Epidemiology Incidence – 150-700/100,000 in adults Increased frequency in children, homosexual males and institutional-care facilities Most common cause of parasite-associated diarrhea in the U.S. Transmission –  waterborne, foodborne, or person-to-person   Organism Protozoal parasite that inhabits the small intestine Clinical Presentation Most infections are asymptomatic Symptoms may last from weeks to months Acute or chronic nonbloody diarrhea, nausea, abdominal discomfort, malabsorptive symptoms (eg, flatulence, greasy malodorous stools) Intermittent or recurrent symptoms are common Treatment May resolve/clear spontaneously in some cases; however, treatment recommended for both symptomatic and asymptomatic disease to reduce transmission Prevention Cooking food adequately Boiling or filtering potentially contaminated water

• Cryptosporidium spp

  Epidemiology Incidence – 20-100/100,000 Increased frequency in HIV infection, households of infected patients, daycare centers, and foreign travel Transmission – waterborne, sporadic or outbreak-associated Organism Protozoan parasite frequently associated with waterborne outbreaks >12 species (genotypes) – C. parvum and C. hominis most common Clinical Presentation Immunocompetent individuals Usually asymptomatic or mild, self-limiting gastroenteritis Nonbloody diarrhea, nausea, vomiting, abdominal pain, low-grade fever and malaise lasting from a few days to occasionally >30 days Immunocompromised individuals Chronic diarrhea (often more severe than expected for pathogen), dehydration, weight loss Treatment Immunocompetent – generally no treatment necessary Immunocompromised and those with severe disease – supportive, no single effective therapy; nitazoxanide may be considered

• Entamoeba histolytica

  Epidemiology Prevalence Estimated 4% of population in industrialized nations infected with E. histolytica Increased frequency in homosexual men, immigrants, institutional-care settings, foreign travel, HIV  patients Sex – M>F for liver abscess disease Transmission – waterborne, foodborne, or person-to-person Organism Enteric protozoa – only E. histolytica considered pathogenic out of Entamoeba spp Clinical Presentation Most individuals are asymptomatically colonized (~90%) Disease may be intestinal or extraintestinal Intestinal disease May be asymptomatic or symptomatic, fulminant or chronic, with abdominal pain, tenderness, tenesmus, and bloody diarrhea Extraintestinal disease May include liver, brain, and lung abscesses Treatment Generally recommended for both symptomatic and asymptomatic individuals to prevent transmission Prevention Treating infected individuals Boiling or filtering potentially contaminated water

• Isospora belli

  Epidemiology Incidence – unknown Increased frequency in HIV  patients, institutional-care settings, daycare centers Transmission – waterborne Organism Coccidian parasite related to Cryptosporidium spp Humans are the only known host and reservoir Clinical Presentation Immunocompetent individuals Acute, self-limiting watery or malodorous diarrhea (similar to Giardia or Cryptosporidium infection) Immunocompromised individuals Chronic diarrhea (occasionally severe), dehydration, weight loss Treatment May be indicated in immunocompromised hosts

• Microsporidia

  Epidemiology Incidence – unknown Increased frequency in HIV patients presenting with chronic diarrhea Transmission – waterborne Organism Obligate intracellular parasites – predominately affects immunocompromised hosts  Includes Enterocytozoon bieneusi, Encephalitozoon intestinalis, Pleistophora, Septata, Vittaforma spp  Clinical Presentation Immunocompetent individuals – rare cause of acute, self-limiting diarrhea Immunocompromised individuals – chronic diarrhea, dehydration, anorexia, weight loss Treatment May be indicated in immunocompromised patients

• Strongyloides stercoralis

  Epidemiology Incidence – unknown in U.S. Increased frequency in endemic areas, institutional-care settings, daycare centers, homosexual males   Transmission – infectious filariform larvae in soil or environment enters body by penetrating the skin Clinical Presentation Cutaneous Serpiginous urticarial rash due to larval migrations, also known as larva currens Cutaneous larva migrans may also be observed with infections by other nematodes such as Ancylostoma spp, Uncinaria stenocephala, and Bunostomum phlebotomum  Pulmonary Symptoms are associated with primary larval migration Increased in hyperinfection with larvae in pulmonary secretions Intestinal Generally asymptomatic, chronic infection Occasionally intermittent diarrhea, abdominal pain Rare – obstruction, ulcers, enterocolitis, malabsorption , hemorrhage, right upper-quadrant pain, sepsis Hyperinfection Frequent in immunocompromised patients Host immunity no longer prevents larval reentry via intestinal wall Disseminated infection with large numbers of larvae found in every tissue of the body Life threatening Treatment Indicated in all cases

Risk Factors

• Testing for parasites should be considered in the following
  • Immunocompromised individuals
  • History of travel or residence in endemic area
  • History suggesting other etiologies such as coccidia (eg, Cyclospora spp, Isospora belli), microsporidia, or other less-common parasites

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory

Diagnostic Algorithm

  Diarrhea, Acute Testing Algorithm