Which statement about Cyclospora cayetanensis oocysts is true?

• A. They are 4–6 μm in size and always acid-fast.
• B. They are 8–10 μm in size, variably acid-fast, and autofluce­sce under UV light.
• C. They are 20–30 μm, non-acid-fast.
• D. They are 12–14 μm, non-ellipsoidal.

Answer: (B)

The important idea here is recognizing how Cyclospora cayetanensis oocysts appear on stool microscopy—specifically their size, staining behavior, and autofluorescence.

Cyclospora oocysts are about 8–10 μm in diameter, which sets them apart from the smaller Cryptosporidium oocysts (4–6 μm) and the larger Isospora oocysts (20–30 μm). They are variably acid-fast, meaning some oocysts will stain with acid-fast stains while others may not, so relying on acid-fast staining alone can miss them. In addition, they autofluoresce under ultraviolet light, producing a characteristic fluorescence that helps confirm their presence when fluorescence microscopy is used.

So this combination—8–10 μm size, variability in acid-fast staining, and UV autofluorescence—best matches Cyclospora oocysts, while the other size and staining descriptions align more with different parasites or are inaccurate for Cyclospora.