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Cystoisosporiasis
What's new
The U.S. Department of Health and Human Services (DHHS) has updated its guidelines for the prevention and treatment of opportunistic infections in adults and adolescents. New recommendations have been issued for primary prophylaxis of cystoisosporiasis in patients with HIV and a CD4 count <200/mcL who live in or are traveling to regions endemic for Cystoisospora belli. The recommended regimens are trimethoprim/sulfamethoxazole 160/800 mg orally either once daily or three times weekly. .
Background
Overview
Definition
Cystoisosporiasis, formerly known as isosporiasis, is an intestinal infection caused by the protozoan parasite Cystoisospora belli.
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Pathophysiology
Infection occurs through ingestion of food or water contaminated with sporulated oocysts. Sporozoites released in the small intestine invade epithelial cells, causing inflammation and malabsorption. The incubation period ranges from several days to over 2 weeks.
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Epidemiology
The prevalence of cystoisosporiasis in patients with HIV is estimated at 2.5% globally.
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Risk factors
Risk factors include immunocompromising conditions, such as HIV/acquired immunodeficiency, and residence in or travel to regions with higher endemicity, such as sub-Saharan Africa.
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Disease course
The disease typically presents with watery, non-bloody diarrhea diarrhea, abdominal pain, anorexia, nausea, vomiting, low-grade fever, and weight loss. In immunocompromised patients, the infection can become chronic and severe, causing severe dehydration, electrolyte abnormalities, such as hypokalemia, and malabsorption. Acalculous cholecystitis and reactive arthritis have also been reported.
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Prognosis and risk of recurrence
In immunocompromised patients, the disease may become chronic and recurrent, often requiring long-term suppressive therapy. Dissemination can involve lymph nodes, liver, and spleen.
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Guidelines
Key sources
The following summarized guidelines for the management of cystoisosporiasis are prepared by our editorial team based on guidelines from the U.S. Department of Health and Human Services (DHHS 2025).
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Medical management
Antimicrobial therapy: as per DHHS 2025 guidelines, administer TMP/SMX 160/800 mg PO or IV QID for 10 days
B
or BID for 7 days as preferred therapy for acute infection. B
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