Cryptosporidiosis

Cryptosporidiosis is a diarrheal illness caused by the protozoan parasite Cryptosporidium (most commonly C. hominis and C. parvum), transmitted via the fecal-oral route. It is self-limited in immunocompetent patients (resolving in ~2–3 weeks) but can cause life-threatening, cholera-like diarrhea in immunocompromised hosts, particularly those with CD4 counts <100 cells/mm³. [1-2] It is a nationally notifiable condition in the United States. [1]

1. History

• Onset and character of diarrhea: Acute/subacute onset of profuse, watery, non-bloody diarrhea (median 12 stools/day in outbreak settings) [3]
• Associated symptoms: Nausea, vomiting, crampy lower abdominal pain, anorexia, fatigue, weight loss, joint pain, headache [3-4]
• Fever: Present in approximately one-third of patients [2]
• Duration: Incubation period 7–10 days (range 2–14 days); symptoms typically last ~2 weeks in immunocompetent hosts but may relapse [1][4]
• Exposure history: Recreational water (pools, water parks, lakes), contaminated drinking water, contact with infected persons or animals (especially pre-weaned calves), daycare exposure, travel to endemic areas, unpasteurized milk/cider [2][4]
• Immune status: HIV status and CD4 count, organ transplant, chemotherapy, primary immunodeficiency [2][5]
• Important negatives: Bloody stool (uncommon — suggests alternative diagnosis), antibiotic use (consider C. difficile), recent travel with raw food ingestion (consider Cyclospora) [3]

2. Alarm Features

• Profuse, voluminous diarrhea with stool output exceeding 10 L/day in severely immunosuppressed patients [2]
• Signs of severe dehydration: Hypotension, tachycardia, oliguria, altered mental status
• Right upper quadrant pain with fever → biliary tract involvement (sclerosing cholangitis, pancreatitis), especially with CD4 ≤50 cells/mm³ [2][4]
• Significant weight loss or failure to thrive (especially in children) [4]
• Known immunocompromised state with persistent or worsening diarrhea
• Respiratory symptoms (cough) — pulmonary cryptosporidiosis may be under-recognized [2]

3. Medications

• Nitazoxanide (Alinia) — FDA-approved for cryptosporidiosis in immunocompetent patients: [6]
  • Adults/adolescents ≥12 years: 500 mg PO BID with food × 3 days [7]
  • Children 4–11 years: 200 mg BID × 3 days (oral suspension)
  • Children 1–3 years: 100 mg BID × 3 days (oral suspension) [4]
  • Limitation: Not shown effective in HIV-infected/immunodeficient patients when used alone [6]
• In HIV/immunocompromised patients: Nitazoxanide 500–1,000 mg PO BID × ≥14 days plus ART (never instead of ART), or paromomycin 500 mg PO QID × 14–21 days plus ART [2]
• Antimotility agents: Loperamide for symptomatic relief; tincture of opium may be more effective [2]
• Octreotide is not recommended — no more effective than oral antidiarrheals [2]
• Contraindicated/caution: Avoid empiric antibiotics for watery diarrhea without identified cause [8]

4. Diet

• Avoid dairy/milk products — diarrhea can cause secondary lactase deficiency [2]
• Aggressive oral rehydration with oral rehydration solutions (ORS) is critical [2]
• Enteral nutrition is preferred; total parenteral nutrition is rarely indicated [2]
• BRAT-type diet and small frequent meals may improve tolerance during acute illness
• Long-term: Monitor nutritional status in children — cryptosporidiosis has lasting adverse effects on growth, particularly when acquired in infancy [4]

5. Review of Systems

• GI: Stool frequency/volume, blood in stool, tenesmus, bloating, flatulence
• Constitutional: Fever, weight loss, fatigue, anorexia
• Hepatobiliary: RUQ pain, jaundice (biliary involvement)
• Respiratory: Cough, dyspnea (pulmonary cryptosporidiosis) [2]
• MSK: Joint pain (reported association) [4]
• Dehydration assessment: Thirst, urine output, dizziness, dry mouth

6. Collateral History and Family History

• Household contacts with similar symptoms (person-to-person transmission is common) [2]
• Daycare or institutional exposure — especially children in diapers [4]
• Occupational exposure: Dairy farmers, veterinary workers, childcare workers [1]
• Sexual history: Men who have sex with men — fecal-oral transmission risk [2]
• Travel history: Countries with less stringent water treatment [4]
• Primary immunodeficiency in family (MHC class II deficiency, CD40L deficiency, hyper-IgM syndrome increase risk for severe disease) [5]

7. Risk Factors

• Immunocompromised state: HIV/AIDS (especially CD4 <100), organ transplant recipients, chemotherapy, primary immunodeficiencies [2][5]
• Age: Children <5 years at highest risk [1][4]
• Recreational water exposure: Swimming pools, water parks, lakes (oocysts resist standard chlorination) [2][4]
• Contaminated drinking water [9]
• Animal contact: Pre-weaned calves, dairy farming [1][4]
• Daycare attendance or employment [4]
• Men who have sex with men [1-2]
• International travel to endemic areas [4]
• Consumption of unpasteurized milk or apple cider [4]

8. Differential Diagnosis

• Giardiasis — also watery diarrhea, bloating, flatulence; more chronic/intermittent; diagnosed by stool antigen/NAAT [1]
• Cyclosporiasis — similar watery diarrhea; linked to imported produce; responds to TMP-SMX [8]
• Cystoisosporiasis (Cystoisospora belli) — watery diarrhea in immunocompromised; eosinophilia may be present [8]
• Norovirus/rotavirus — acute onset, shorter duration, often with prominent vomiting; no specific treatment
• Bacterial gastroenteritis (Salmonella, Campylobacter, ETEC) — more likely with bloody stool, high fever, shorter incubation [8]
• C. difficile — antibiotic exposure history; toxin testing
• Microsporidiosis — chronic diarrhea in advanced HIV; modified trichrome stain [8]
• CMV colitis — in advanced HIV; diagnosed by colonoscopy with biopsy [8]
• MAC — in advanced HIV; systemic symptoms, diagnosed by blood cultures [8]
• Medication-related diarrhea — ART or chemotherapy side effects [8]

Pearl: Neither clinical history nor physical examination reliably differentiates cryptosporidial disease from other causes of infectious diarrhea. [4]

9. Past Medical History

• HIV/AIDS — CD4 count and ART status are critical determinants of severity [2]
• Organ transplantation or other immunosuppressive therapy
• Primary immunodeficiency (especially T-cell defects) [5]
• Malignancy on chemotherapy
• Prior episodes of cryptosporidiosis (recurrence after apparent resolution is common) [4]
• Chronic GI conditions (IBD, IBS — may confound presentation)
• Malnutrition — worsens outcomes, especially in children [4]

10. Physical Exam

• Vital signs: Tachycardia, hypotension (dehydration), fever (~33% of cases) [2-3]
• General: Wasting, cachexia (chronic/immunocompromised cases)
• Mucous membranes: Dry (dehydration assessment)
• Abdomen: Diffuse tenderness, hyperactive bowel sounds, non-peritoneal; RUQ tenderness suggests biliary involvement [4]
• Skin turgor: Decreased with dehydration
• Rectal exam: Watery stool, no gross blood expected
• Pediatric: Assess growth parameters, fontanelle (infants), capillary refill

11. Lab Studies

• Stool testing (must specifically request Cryptosporidium — not included in routine O&P): [1][8]
  • Multiplex molecular panel (NAAT/PCR): Becoming standard of care; sensitivity ~97%, specificity ~98% [4][8]
  • Direct fluorescent antibody (DFA): Sensitivity/specificity 99.8–100% — reference standard [1]
  • Stool antigen (EIA): Sensitivity 66–100%; some rapid immunochromatographic tests have poor specificity [2][4]
  • Modified acid-fast stain: ~70% sensitivity; lower than molecular methods [10]
• BMP/CMP: Electrolytes (hypokalemia, hyponatremia, metabolic acidosis from volume loss), renal function
• CBC: Leukocytosis is variable; eosinophilia is not typical
• Alkaline phosphatase: Elevated with biliary tract involvement [1][4]
• HIV testing if status unknown — critical for management decisions
• CD4 count if HIV-positive [2]
• Repeat stool sampling (3 consecutive days) recommended for milder disease, as oocyst excretion can be intermittent [2][4]

12. Imaging

• Not routinely indicated in uncomplicated cases
• RUQ ultrasound or CT abdomen: If biliary involvement suspected — may show enlarged gallbladder with thickened wall, dilated biliary ducts, pericholecystic fluid [1][4]
• ERCP: For diagnosis and potential therapeutic intervention (sphincterotomy, stenting) in biliary tract disease [2]

13. Special Tests

• Multiplex GI pathogen panels (e.g., BioFire FilmArray) — increasingly used as first-line; detect Cryptosporidium along with other enteric pathogens [4]
• Intestinal biopsy: Can diagnose cryptosporidial enteritis from tissue sections; reserved for unclear cases [2]
• Molecular subtyping (gp60 gene sequencing): Used for outbreak investigation and species identification; requires unfixed stool [4]
• Serology: Not used for acute diagnosis; used in epidemiologic studies [10]

14. ECG

• Not routinely indicated unless significant electrolyte derangements (hypokalemia, hypomagnesemia) from profuse diarrhea
• Monitor for QT prolongation and arrhythmia risk in patients with severe electrolyte losses

15. Assessment

Severity stratification depends primarily on immune status

Complications: Severe dehydration, electrolyte derangements, malnutrition/growth stunting (children), sclerosing cholangitis, pancreatitis, pulmonary disease. [2][4]

16. Treatment Plan

Immunocompetent patients

• Supportive care: Aggressive oral rehydration, electrolyte replacement [1-2]
• Antimotility agents: Loperamide PRN for symptom control
• Nitazoxanide if symptoms persist >2 weeks: 500 mg PO BID with food × 3 days [1][7]
• Retest if symptoms continue after treatment to assess for persistent infection or reinfection [1]

HIV/Immunocompromised patients

• Initiate or optimize ART — this is the mainstay of treatment; immune reconstitution to CD4 >100 cells/mm³ typically leads to resolution [2]
• Aggressive IV/oral rehydration and electrolyte repletion [2]
• Antimotility agents: Loperamide; tincture of opium may be more effective [2]
• Nitazoxanide 500–1,000 mg PO BID with food × ≥14 days plus ART [2]
• Alternative: Paromomycin 500 mg PO QID × 14–21 days plus ART [2]
• Biliary disease: ERCP with possible sphincterotomy/stenting [2]
• Nutritional support: Enteral nutrition preferred; avoid dairy [2]

Pediatric dosing (nitazoxanide): [4]

• 1–3 years: 100 mg BID × 3 days
• 4–11 years: 200 mg BID × 3 days
• ≥12 years: 500 mg BID × 3 days

17. Disposition

• Discharge criteria (most immunocompetent patients):
  • Tolerating oral fluids
  • Stable vital signs, no orthostasis
  • Adequate urine output
  • Reliable follow-up and return precautions understood
• Admission criteria:
  • Severe dehydration not responsive to oral rehydration
  • Inability to tolerate oral intake
  • Significant electrolyte abnormalities
  • Immunocompromised with profuse diarrhea (stool volumes can exceed 10 L/day) [2]
  • Biliary tract involvement (RUQ pain, elevated ALP, fever) [4]
  • Pediatric patients with signs of moderate-severe dehydration or failure to thrive
• Specialist consultation triggers:
  • Infectious disease: Immunocompromised patients, treatment failure
  • GI/hepatology: Biliary tract disease requiring ERCP [2]
  • Pediatrics/nutrition: Children with growth failure or malnutrition
• Public health notification: Cryptosporidiosis is a nationally notifiable disease — report to local health department [1]

18. Follow Up / Return Precautions

• Follow-up timing:
  • Immunocompetent: 1–2 weeks if symptoms persist; retest stool if diarrhea continues after treatment [1]
  • Immunocompromised: Close follow-up within 1 week; monitor CD4 response to ART
• Return immediately for:
  • Inability to keep fluids down
  • Bloody stool (suggests alternative/co-diagnosis)
  • High fever, severe abdominal pain, RUQ pain
  • Signs of dehydration (dizziness, decreased urine output, confusion)
  • Worsening or recurrent symptoms after initial improvement
• Patient counseling:
  • Highly contagious — strict hand hygiene (alcohol-based sanitizers are NOT effective against oocysts; soap and water required)
  • Avoid swimming pools/recreational water for 2 weeks after diarrhea resolves (oocysts are chlorine-resistant) [2][4]
  • Avoid preparing food for others while symptomatic
  • Avoid dairy products during acute illness [2]
• Expected recovery: Immunocompetent patients typically recover within 2–3 weeks; symptom recurrence after apparent resolution is common. Immunocompromised patients require immune reconstitution for durable cure. [2][4]

References

1. Common Intestinal Parasites. — Pyzocha N, Cuda A. American Family Physician. 2023.

2. Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents With HIV. — Constance Benson, John Brooks, Shireesha Dhanireddy, et al Infectious Diseases Society of America; Office of AIDS Research Advisory Council (2025). 2025.

3. Cryptosporidiosis. — Chen XM, Keithly JS, Paya CV, LaRusso NF. The New England Journal of Medicine. 2002.

4. Guidelines for the Prevention and Treatment of Opportunistic Infections in Children With and Exposed to HIV. — Bill G. Kapogiannis, Franklin Yates, Wei Li, et al Office of AIDS Research Advisory Council (2025). 2025.

5. Immunity to Cryptosporidium: Lessons From Acquired and Primary Immunodeficiencies. — Cohn IS, Henrickson SE, Striepen B, Hunter CA. Journal of Immunology. 2022.

6. FDA Drug Label. — Updated date: 2024-03-20. Food and Drug Administration.

7. FDA Drug Label. — Updated date: 2025-12-30. Food and Drug Administration.

8. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. — Shane AL, Mody RK, Crump JA, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2017.

9. Waterborne Diseases That Are Sensitive to Climate Variability and Climate Change. — Semenza JC, Ko AI. The New England Journal of Medicine. 2023.

10. A Review of the Global Burden, Novel Diagnostics, Therapeutics, and Vaccine Targets for Cryptosporidium. — Checkley W, White AC, Jaganath D, et al. The Lancet. Infectious Diseases. 2015.