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- Obligate intracellular coccidian parasite; infects epithelial cells of small intestine.
- Excreted in stool as oocysts (spherical, 8-10 μm in diameter), which may be shed intermittantly and at low levels. Sporulation (maturation of oocysts) occurs outside host and takes 7-12d.
- Transmitted by fecal-contaminated soil, food and water. Humans only known host and reservoir. Human-to-human transmission unlikely as excreted oocysts must sporulate before becoming infectious. 
- Both sporadic infections and outbreaks occur. Infections tend to be seasonal with spring & summer being peak seasons in the U.S., associated with imported raspberries, mixed salad greens, and basil. 
- Found in travelers to endemic areas, i.e., Peru, Nepal, Haiti, Guatemala, Indonesia.