Table 1.

Overview of protozoal infections causing gastroenteritis

Parasite	Geographic Region	At-risk Populations	Symptoms	Diagnosis	Treatment
Giardia	Worldwide, usually due to contaminated surface water	Affects both immunocompetent and immunocompromised	Bloating and diarrhea	Stool examination for trophozoites and cysts	Metronidazole, 500 mg, twice daily for 5–7 d
Cryptosporidiosis	Worldwide	Affects both immunocompetent and immunocompromised but prolonged and more severe infection in immunosuppressed individuals (AIDS or organ transplant recipients)	Profuse diarrhea	ELISA for Cryptosporidia antigen	Supportive care for immunocompetent patients Can consider nitazoxanide or trimethroprim-sulfamethoxazole if immunocompromised
Cystoisospora	Tropical and subtropical climates	Immigrants and immunosuppressed patients (AIDS)	Nonbloody diarrhea	Direct visualization of oocysts in stool	Trimethroprim-sulfamethoxazole
Amebic dysentery	Tropical climate, more common in areas with poor sanitation	Men who have sex with men	Abdominal pain Bloody diarrhea	Identification of trophozoits and cysts in stool	Metronidazole, 500–750 mg, 3 times daily for 10 d + intraluminal agent