Cryptosporidiosis
Cryptosporidiosis is intestinal infection by the chlorine-resistant protozoan Cryptosporidium, acquired from fecally contaminated water (classically swimming pools and municipal supplies), food, people, or animals. It causes self-limited watery diarrhea of under 2 weeks in healthy hosts but chronic, wasting diarrhea in AIDS with CD4 counts below 100/µL; diagnosis requires a Cryptosporidium-specific stool test, and treatment is rehydration, nitazoxanide 500 mg PO twice daily for 3 days for severe or prolonged disease, and antiretroviral therapy in HIV.
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What this article covers
- Overview
Definition: Cryptosporidiosis is small-intestinal infection by the protozoan Cryptosporidium (principally Cryptosporidium parvum), transmitted fecal-orally as thick-walled oocysts.
- Epidemiology
Common parasitic diarrhea: Giardiasis, amebiasis, and cryptosporidiosis are the most common parasitic diarrheas in the United States.
- Risk factors
Advanced HIV infection: CD4 count below 100/µL is the strongest risk for chronic, severe disease.
- Pathophysiology
Ingestion of oocysts: Thick-walled oocysts in water or food survive chlorine and can evade filtration.
- Clinical features
Hallmark: Profuse, nonbloody watery diarrhea with abdominal cramping beginning about 7 days after exposure.
- Differential diagnosis
Cytomegalovirus colitis in AIDS: Frequent bloody diarrhea with abdominal pain at CD4 counts below 50/µL and linear ulcers on endoscopy, unlike the nonbloody stool of cryptosporidiosis; see cytomegalovirus.
- Diagnosis
What establishes the diagnosis: Cryptosporidiosis is confirmed by a Cryptosporidium-specific stool test: oocysts on modified acid-fast stain, stool antigen enzyme immunoassay (sensitivity 87%…
- Management
First, rehydrate: Give oral rehydration solution to replace losses volume for volume, about 75 mL/kg over the first 4 hours for moderate dehydration, then match ongoing stool losses until diarrhea…
- Complications
Severe dehydration and electrolyte loss: Voluminous diarrhea in AIDS causes volume depletion and acute kidney injury.
- Prognosis
Immunocompetent hosts: Full recovery is the rule, with symptoms resolving spontaneously in under 2 weeks.
- Prevention
Recreational water exclusion: Anyone treated for cryptosporidial diarrhea avoids public pools for 2 weeks after diarrhea resolves, because the parasite persists for days in chlorinated water.
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Giardiasis is infection of the proximal small bowel with the protozoan Giardia lamblia (duodenalis), acquired from cysts in contaminated fresh water or food, causing malabsorptive, foul-smelling, greasy diarrhea with bloating and weight loss over weeks. Diagnosis rests on a stool antigen or nucleic acid test, and treatment is a short course of tinidazole, metronidazole, or nitazoxanide.
- Gastrointestinal complications of HIV infection
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- HIV antiretroviral therapy (ART)
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- Norovirus infection
Norovirus is the most common cause of acute gastroenteritis in the United States, producing watery, noninflammatory diarrhea with prominent vomiting after a short incubation period, spreading efficiently via the fecal-oral route with an infectious dose under 100 viral particles and viral shedding for up to two weeks after symptoms resolve; diagnosis is clinical or by nucleic acid amplification testing, and treatment is entirely supportive oral or IV rehydration since no antiviral or antimicrobial therapy exists.
- Cytomegalovirus (CMV) infection
Cytomegalovirus is a ubiquitous herpesvirus that is usually asymptomatic or causes a heterophile-negative mononucleosis-like illness in healthy hosts, but reactivates to cause retinitis, colitis, pneumonitis, or encephalitis in transplant recipients and patients with AIDS; treatment is systemic ganciclovir or valganciclovir, with foscarnet and cidofovir reserved for resistance or intolerance.
- Hyper-IgM syndrome
Hyper-IgM syndrome is a class-switch recombination defect, most often X-linked CD40 ligand deficiency, causing normal or high IgM with very low IgG, IgA, and IgE and severe pyogenic and opportunistic infections early in life. Diagnosis rests on the immunoglobulin pattern with impaired switching, and treatment is immunoglobulin replacement, Pneumocystis prophylaxis, and consideration of stem cell transplantation.